chem 101 lab manual

Department of Chemistry

2012 FIRST YEAR CHEMISTRY LABORATORY MANUALDaniel Southam Director of First Year Studies, Department of Chemistry

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In case of an emergency dial 5 from any fixed-line phone on campus. All other phones use 08 9266 4444 or 1300 00 4444.

Write the name and contact information for your demonstrator and supervising demonstrator in the space below. This should be your first contact if a problem arrises in the laboratory. My demonstrator Name Email The experiments in this laboratory manual may not be performed in the order in which they are found or in a numeric sequence. Please refer to your unit outline for the correct sequence and ensure you bring the full laboratory manual to every laboratory session. My supervising demonstrator

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This laboratory manual has been revised and updated with the kind assistance of your demonstrators, technicians and lecturers.

No part of this manual may be reproduced without the written permission of the Department of Chemistry COMMONWEALTH OF AUSTRALIA Copyright Regulation 1969 WARNING This material has been copied and communicated to you by or on behalf of Curtin University of Technology pursuant to Part VA of the Copyright Act 1968 ( the Act). The material in this communication may be subject to copyright under the Act. Any further copying or communication of this material by you may be the subject of copyright or performers' protection under the Act. Do not remove this notice

TABLE OF CONTENTSIntroduction Safety Care and use of balances A guide to uncertainties in volumetric analysis Advancing Science by Enhancing Learning in the Laboratory (ASELL) Part 1: Principles of chemistry and chemical measurementExperiment 1.1: Introduction to the laboratory Chemical puzzles Experiment 1.2: Determination of acetic acid in vinegar Experiment 1.3: Standardisation of hydrochloric acid with borax Experiment 1.4: Standardisation of hydrochloric acid with a standard solution of sodium carbonate Experiment 1.5: An introduction to organic chemistry

5 7 11 12 16 1719 33 45 53 61

Part 2: Chemistry of the elementsExperiment 2.1: Identication of common ions in solution Experiment 2.2: Simulation of extraction of gold from its ores Experiment 2.3: Coordination chemistry Synthesis of metal acac complexes Experiment 2.4: Hard soft acid base theory

7577 89 99 115

Part 3: Synthesis, isolation & puricationExperiment 3.1: Identication of components in a mixture by chromatography Experiment 3.2: Purication of benzoic acid by recrystallisation Experiment 3.3: Preparation and reactions of cyclohexene Experiment 3.4: Preparation of 4-nitroacetanilide Experiment 3.5: Carboxylic acids and their derivatives using mind maps to link concepts Experiment 3.6: Alcohols and phenols

137139 151 163 173 181 193

Part 4: Chemical and physical changesExperiment 4.1: Intermolecular forces Solubility in liquids Experiment 4.2: Designing and making buffer solutions Experiment 4.3: Kinetics of the iodine clock reaction Experiment 4.4: Exploring Hess law using calorimetry

203205 217 225 243

Part 5: Techniques in quantitative analysisExperiment 5.1: Atomic Absorption Spectrometry Experiment 5.2: Determination of vanillin in imitation vanilla essence Experiment 5.3: Gas Chromatography Experiment 5.4: Analysis of vegetable oils Experiment 5.5: Determination of iron in cereals Experiment 5.6: Analysis of vitamin C

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INTRODUCTIONAssessment and attendanceIn addition to gaining at least 50% of the total marks, to gain a pass in this unit you must complete at least 80% of the available experiments and gain at least 50% of the total laboratory marks. Students who are absent from the laboratory due to illness, University business or participation in the Elite Athletes Program may be granted an exemption from an experiment at the discretion of the Unit Coordinator or the Head of the Department of Chemistry. If you were absent from the laboratory due to one of the aforementioned reasons, you should complete an Absence from the Laboratory form available from FLECS- Blackboard and attach the requisite documentary evidence. If approved, exemptions do not count toward the total number of laboratories for this pass requirement or the total laboratory mark. All requests for exemption must be received within ten working days of the missed laboratory. In many exercises, there are pre-laboratory questions to be answered prior to attending the laboratory class. These pre-laboratory questions must be handed in prior to the commencement of the pre-laboratory presentation. Pre-laboratory questions are an important part of the laboratory program to such an extent that two marks will be deducted from any exercise where they have not been attempted. All calculations are to be shown in full. In some experiments, students will be assessed on their accuracy, so pay particular attention to your technique.

Laboratory notes and pre-laboratory presentationsBefore you commence an experiment, you should be fully aware of the hazards associated with the reagents and equipment you are about to use. To assist you with this, you must read and understand the procedures in this laboratory manual before entering the laboratory. This manual has notices throughout that highlight some important information, for example the safety requirements for a procedure you are about to perform.

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The procedure you are about to perform contains a hazard. Safety is your responsibility. Take care!

Hazards are highlighted in the pre-laboratory presentation given by your demonstrator at the commencement of the laboratory. If you are not present at this presentation, you can put yourself and your fellow students at risk of injury. If you arrive after the pre-laboratory presentation, your demonstrator has the right to bar your entry to the laboratory, you will not be able to perform the experiment and you risk receiving zero for the missed experiment.

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The experiments in this laboratory manual may not be performed in the order in which they are found or in a numeric sequence. Please refer to your unit outline for the correct sequence and ensure you bring the full laboratory manual to every laboratory session.

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EquipmentTo work in the laboratories, you must have the following items and be wearing them at all times in the laboratory. Laboratory coat Safety glasses Fully enclosed at-soled shoes covering the forefoot, toe and heel. Thongs, sandals, ballet slippers, ugg boots or similar are not acceptable.

Students who are not correctly attired will not be permitted entry to the laboratory and risk getting zero for the experiment. Forgetting these items does not warrant an excuse to gain an exemption under any circumstances. Laboratory coat and safety glasses only are available for hire at your cost from the technical staff. Students without correct footwear will not be permitted into the laboratory and will not necessarily be able to attend another session. The following items are recommended, particularly for students progressing to second year chemistry: Spatula, preferably metal Permanent marker, for marking of glassware

Contacts Dr Daniel Southam Director of First Year Studies Ms Alicia Harrison Student Support Officer 08 9266 7265 [email protected] Reception, Level 2, Building 500

Telephone: Email: Location:

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SAFETYAn important part of the laboratory experience is learning to work safely. Safety is everyones responsibility while in the laboratory. Even if youre not working with chemicals other people may be, so be aware at all times and follow some simple rules to avoid injury or causing injury to others. At the beginning of each experiment, you will see some important notices in the laboratory manual about safety. Failure to follow these and the instructions of staff may put you or other people at risk of injury. Students who fail to follow instructions will be asked to leave the laboratory and may face disciplinary action. The laboratory manual contains three important types of notices that must be read and understood before you commence any procedure in the laboratory:

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A warning about specific hazards in this laboratory will be mentioned in these notices. This will occur both at the commencement of the laboratory and throughout the procedure. Many injuries can be avoided by following the verbal and written instructions from your demonstrator and in the laboratory procedure. If youre not sure, please ask staff for clarification.

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All staff and students must wear the minimum Personal Protective Equipment (PPE) at all times whilst in the laboratory: safety glasses, a laboratory coat and fully enclosed shoes covering the forefoot, toe and heel. Additional or specialised PPE may be required when handling some equipment and chemicals.

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Stop notices are used to draw your attention to a particular procedure which must be carefully followed to ensure your experiment works well and marks are not lost.

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11 simple rules for safety in laboratories

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The primary rule for safety in an undergraduate laboratory is to follow the instructions of all staff at all times. Demonstrators in the laboratory can be identified by their yellow safety vests. Other technical staff will be introduced to you in the first lab. It is a requirement that you follow their instructions without exception. Always act responsibly. Horseplay, running, unauthorised experiments etc. are strictly forbidden. Appropriate clothing must always be worn. This includes as a minimum: Safety glasses with colourless transparent lenses. Personnel wearing contact lenses must inform the laboratory supervisor as special precautions may be required. Neither sunglasses nor common prescription glasses are acceptable. A laboratory coat of a type that fastens up the front and comes to above the knee. Fully enclosed water-resistant shoes covering the forefoot, toe and heel completely. Thongs, sandals, ballet slippers, ugg boots or similar are not acceptable. Disposable gloves are available and must be worn as required. Ask your demonstrator to ensure the appropriate gloves are being used. Long hair should be tied up, regardless of gender. Any person wearing a headscarf or hijab should take extra care to ensure it is tucked into the laboratory coat.

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No food or drink is to be handled or consumed in a laboratory. Do not smoke in any place on campus. All buildings and grounds are smoke free. Never undertake any work unless the hazards of the operation are known and the safety precautions adopted. Students will be made aware of the risks during the pre-laboratory presentation at the beginning of the laboratory session. The instructions given by any member of staff regarding safety must be obeyed without question. You may be barred from the laboratory if you miss the pre-laboratory presentation at the discretion of the demonstrator.

6. 7. 8. 9. 10.

Always use protective devices appropriate to the type of operation being carried out, giving consideration to personnel operating in your vicinity. Regard all substances as hazardous unless there is denite information to the contrary. Report all accidents and spills, no matter how trivial, to your demonstrator. Ensure all spills are cleaned up immediately. Immediately wash skin areas which come into contact with chemicals, irrespective of concentration, and report this to your supervisor. Always use a fume hood when working with highly toxic, volatile or odourous substances. You will be given instructions by your demonstrator about the use of certain chemicals in the fume hood. Please ensure they are followed at all times. Dispose of specialised wastes (e.g. broken glassware) in containers reserved for the particular type of waste.

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Chemical Hazards1. All chemicals should be handled with care. The following are particularly hazardous:8

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Concentrated acids, e.g. sulfuric, nitric; concentrated alkalis, e.g. sodium hydroxide, aqueous ammonia; hydrofluoric acid, chlorine, bromine, phenols, benzene, sodium or potassium metal, hydrogen sulfide gas. In case of spillage or splashing: (a) (b) (c) (d) 2. 3. on skin - wash off immediately under the nearest tap. on clothing - remove clothing and rinse thoroughly in water. on floor or bench - dilute with water and mop up with paper towels or mop. in eye - wash immediately with the eye irrigators situated at eye wash station.

Organic solvents, if in continual contact with skin, can cause skin diseases such as dermatitis. All experiments likely to generate toxic, flammable or irritating gases must be carried out in a fumehood. You will be instructed by your demonstrator in the pre-laboratory presentation which steps in the procedure require a fumehood. Particular care should be exercised in disposing of waste or spilt chemicals and reaction residues. This should be done on the advice of your demonstrator. Rubbish, waste filter paper, used paper towels etc must not be thrown into sinks or yellow sharp waste bins but placed in the green general waste bins with black liner provided. All sharp and/or contaminated wastes, such as broken glassware, must be placed in the yellow sharp waste bins.

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For a more complete list of chemicals with their first aid treatment, consult the Safety Data Sheets (SDS) available from ChemAlert at the PC located in the level 4 corridor.

Fire hazards1. 2. Every student should learn from the demonstrator where to find the fire blanket, and fire extinguisher, nearest their place of work. Clothing catching fire causes the most distressing laboratory accidents. Since the victim's chances of recovery rapidly diminish with the extent of skin surface burned, immediate and correct action is essential. When clothing catches fire, throw the person to the floor and roll to smother the flames quickly. If a fire blanket or a laboratory coat is very handy, it may be used. If near a shower, roll the person under and then turn on the water, but never let them stand even if you have to be forceful. This procedure prevents injury to the respiratory passages and eyes by the flames, which would naturally rise and envelop the head. Never use an extinguisher of any type on a person. The soda-acid extinguisher may damage the eyes, whilst the carbon dioxide type may cause severe frostbite. 3. Flammable liquids should never be handled near an open flame, including when used in fumehoods. Never distil solvents such as alcohol, ether, petrol, etc. over or near an open flame. Volatile vapours will travel many metres to an open flame and ignite, thus setting the liquid in the container alight. Students are advised to tie up long hair since loose flowing hair may be a serious fire hazard in a chemical laboratory. Similarly, a headscarf or hijab may pose an extra risk, so extra care should be taken by tucking it into your laboratory coat.

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Handling glasswareThe most common laboratory accidents arise from the careless handling of glassware. The following rules must be observed: 1. Ensure there are no jagged or chipped edges. Do not use glassware that is broken, chipped or damaged. Report any damaged glassware to your demonstrator or a technician. Before inserting glass tubing into corks, rubber tubing, or stoppers, make sure that the hole is large enough and moisten the tubing or stopper. Hold the stopper, etc., between thumb and forefinger, not in the palm of the hand. Grasp the glass tubing close to the end that is to fit into the stopper and push the tubing with an even pressure. Glycerine may be used as a lubricant instead of water. Never use force to remove rubber or corks from glass tubing. If necessary, cut the rubber or cork away from the glass. Do not try to force an oversize stopper into a flask.

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Approximate concentrations of some laboratory reagents1. Concentrated Reagents (in fumehoods) Name Hydrochloric Acid Nitric Acid Sulfuric Acid Glacial Acetic Acid Aqueous Ammonia Sodium Hydroxide 2. Formula HCl HNO3 H2SO4 CH3COOH NH3 NaOH Molarity 10.2 16 18 17.4 14 9 % w/w 32 70 95 99.5 28 36 S.G. 1.16 1.42 1.84 1.04 0.89

Dilute Aqueous Reagents (on benches) Name Hydrochloric Acid Nitric Acid Sulfuric Acid Aqueous Ammonia Sodium Hydroxide Molarity 3 3 3 3 3

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CARE AND USE OF BALANCESThe balances in our laboratories are expensive and fragile apparatus. Extra care must be taken when using them and the following rules are to be observed. 1. 2. 3. 4. Report any fault in balance operation to the laboratory technician. Do not try to rectify faults yourself. The glass doors at the sides of the balance case must be closed during weighing since drafts will upset the measurement. Before weighing, ensure that the pan is clean and dry and examine the object you are weighing to see that it is not wet or dirty on the outside. Take your laboratory notebook and record all weighings immediately. Do not rely on your memory or on scraps of paper. Check that the weight has been written correctly. It may save you hours repeating the experiment. Chemicals must not be weighed directly on the balance pan. Always use a suitable container such as a weighing bottle (see below) or crucible. Both weights, not merely the weight of substance, must be recorded. Anything spilt in the balance must be brushed out immediately. The bench on which the balance sits must also be kept free of spilt chemicals. Warm or hot objects must not be weighed. Convection currents in the air within the balance will cause errors. These are known as buoyancy errors. Objects placed on the balance pan are subject to the upthrust of the air that their volume displaces. A stoppered vessel will weigh less in the laboratory than in a vacuum. Corrections for buoyancy should be applied to substances of low density such as water. Further errors may be caused by samples that evaporate or absorb moisture.

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Steps involved in weighing1. Whenever possible a weighing bottle should be used. If the quantity of solid to be weighed exceeds the capacity of the weighing bottle, a 50 mL or 100 mL beaker should be used - never use a watchglass. Remove the weighing bottle from the balance - never weigh any materials directly into a container on the balance. Weigh out approximately the required weight of the substance into a clean weighing bottle and record the total weight. Transfer the contents of the weighing bottle to a beaker, crucible, etc. Re-weigh the weighing bottle containing any remnants of the substance that did not come out in the transfer stage in 3 above and record the weight. By subtraction, the weight of substance transferred can be accurately determined.

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This method of weighing is known as weighing by difference. You should use this technique at all times in these experiments.

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A GUIDE TO UNCERTAINTIES IN VOLUMETRIC ANALYSISWhen the result of a determination is presented, some indication should be given of the limits of accuracy. The first indication of the accuracy of a result is the way the relevant figure is written. For example, the Avogadro constant, NA, is written as 6.023 1023 mol1. This indicates that the value is known to at least four significant figures, i.e. the fourth figure, the 3, has some meaning. The table below lists ten separate readings that illustrates this uncertainty in measurement. No. 1 2 3 4 NA 6.025671 1023 6.021902 1023 6.024008 1023 6.022319 1023 No. 5 6 7 8 NA 6.023912 1023 6.023006 1023 6.020978 1023 6.022702 1023 No. 9 10 NA 6.024181 1023 6.023409 1023

These figures average 6.0232088 1023, yet they certainly would not justify writing NA as 6.0232088 1023. The results give the number as somewhere between 6.021 1023 and 6.026 1023, and the average should be written as 6.023 1023. As the 3 is uncertain, writing the 2088 part of the figure would imply accuracy not actually achieved. If a measurement is repeated many times, statistical methods may be used to determine the uncertainty of the result. Usually a determination is made only once or in duplicate, and other methods are needed to estimate accuracy. These methods are based on a consideration of the uncertainty in each measurement involved in the determination, and an estimation of their effect on the accuracy of the final figure. There are two broad classes of uncertainty - systematic uncertainty and random uncertainty. Systematic uncertainty will always act in the one direction. Examples are uncertainties in weighing hygroscopic (water absorbing) samples (always positive) or in weighing volatile samples (always negative). It is often possible to cope with these uncertainties by one of two methods: 1. 2. They can be minimised by improvements in technique, e.g. weighing more rapidly, etc. They can be allowed for by correction factors. In a titration of acid into base a little acid is required to change the colour of the indicator - apart from that required to neutralise the base. By titrating acid into distilled water plus indicator an estimate of this indicator or blank uncertainty can be made and subtracted from all titration figures. This technique cannot always be applied, e.g. the weighing uncertainty for hygroscopic samples will vary according to size and surface area of sample, time taken in weighing, humidity, room temperature, etc.

Random uncertainty can act in any direction. It is brought about by uncontrolled variables. For example, a pipette may deliver up to 0.02 mL too much or too little - even if care is taken.

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In this laboratory manual the following random uncertainties should be allowed for:

Weighing 0.001 g on a 3-decimal place balance.

Pipette 0.05 mL for a 20 mL pipette. For more accurate work, the manufacturer's uncertainty can be determined by calibrating the pipette, leaving a random delivery uncertainty of 0.02 mL for a 20 mL pipette.

Burette 0.05 mL for each reading.

Volumetric asksAssume an overall uncertainty of 0.2mL per 100mL capacity. An uncalibrated 250mL volumetric flask would give an uncertainty of 0.50 mL. The relative uncertainty is always 0.2%.

Steps for Calculating UncertaintyRule 1 Rule 2 When two figures are added or subtracted, the absolute uncertainty in the answer is the sum of the individual absolute uncertainties. When two figures are multiplied or divided, the relative (%) uncertainty in the answer is the sum of the individual relative (%) uncertainties.

For a simple titrimetric analysis: 1. Identify sources of uncertainty, which include any piece of apparatus that you are relying on a value to calculate from. Each apparatus has an inherent uncertainty in its reading or tolerance. This includes volumetric glassware like pipettes and volumetric flasks, balances or analytical instrumentation. For example, for apparatus used in these laboratories: Balance 0.001g per reading for 3-decimal place balance, giving total uncertainty of 0.002 g for each mass (when using weigh by difference, each number has uncertainty) 0.05 mL for a 20 mL pipette 0.05mL for each reading, giving total uncertainty of 0.10mL per titre 0.2 mL per 100 mL capacity; relative uncertainty always 0.2%

Pipette Burette Volumetric Flask 2.

Calculate the value of each uncertainty as a percentage

where

The uncertainty value is the value The measured value is the mass, titre, volume, etc

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This describes the relative uncertainty associated with each measurement as a percentage. Only relative uncertainties can be combined to calculate the total uncertainty associated with each part of an experiment, since units are eliminated. 3. 4. Calculate total percentage uncertainty for the experiment by adding up the relative uncertainty for each source Calculate the absolute uncertainty on the final answer for the experiment Absolute uncertainty = % uncertainty calculated answer Quote as calculated answer absolute uncertainty with units e.g. 1. 2. 0.100 0.001 M 0.223 0.003 g L1

ExampleSodium hydroxide solution was standardised by titration of a 10.02 mL sample (from a calibrated pipette) with 0.102 0.002 M hydrochloric acid. The titration readings were: Final reading Initial reading Volume delivered (Titre) 45.20 mL 0.05 mL 34.30 mL 0.05 mL 10.90 mL

From Rule 1, uncertainty in titre due to reading uncertainty is: 0.05 mL + 0.05 mL = 0.10 mL The molarity of the NaOH solution is given by: From Rule 2, the relative (%) uncertainty in 0.1109 M is the sum of the relative uncertainties in 0.102, 10.90 and 10.02. This can be set out as follows: Uncertainty (mL) Molarity Burette (mL) Pipette (mL) 0.102 10.90 10.02 0.002 0.10 0.02 Relative Uncertainty (%) 2.0 0.9 0.2 3.1 3.1% of 0.1109 M = 0.0034 M

The answer should be expressed only to the first uncertain figure, in this case the third decimal place. The uncertainty should be rounded off to one significant figure and however many decimal places this produces, determines the number of decimal places in the answer. In this case, 0.111 0.003 M

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Notes on uncertaintiesDeterminations are usually based on duplicates. In general it is satisfactory to calculate the uncertainty in one of the duplicates and apply this to the mean result. If the two results differ by more than twice the calculated uncertainty, they are not close enough and another determination should be carried out. The uncertainties expressed are based only on predictable random uncertainties. Uncertainties due to careless work are not accounted for, nor are systematic uncertainties. Variable systematic uncertainties may appear as too divergent in the duplicates. Constant systematic uncertainties are obscured. The above rules are a simplified treatment and tend to exaggerate those uncertainties that are due to predictable random causes.

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ADVANCING SCIENCE BY ENHANCING LEARNING IN THE LABORATORY (ASELL)Why?Laboratory activities have long been seen as important components of a science course. They can be a popular component of these courses and can stimulate and motivate students to learn more about science. Indeed, most educators agree that the laboratory experience consistently ranks highly as a contributing factor toward students interest and attitudes to their science courses. Consequently, good laboratory programs should play a major role in influencing student attitudes, learning and performance. In fact the laboratory program can define a student's experience in the sciences, and if done poorly, can be a major contributing factor in causing students to disengage from the subject area. The challenge remains to provide students with laboratory programs that are relevant, engaging and offer effective learning outcomes.

How?Curtin University is an active participant in the ASELL research project, with Prof. Mark Buntine (Head of Chemistry) a co-director of this national project and several other members of staff in the School of Science heavily involved. Over the course of this year we will ask you to complete surveys on the experiments you have undertaken and then the program as a whole. Your participation is voluntary and the surveys are anonymous. Nonetheless, you will be asked to identify the experiment you are evaluating and/or the unit in which you are enrolled. Neither whether you choose to respond to the survey, nor any feedback you provide, will have any influence whatsoever on your progress, results or grades in this unit. Returning the survey will constitute consent for its use for research purposes. The confidentiality of the information you provide will be safeguarded subject to any legal requirements. The results from this research will be used to improve undergraduate laboratory programs across Australia, and may be published in both refereed and non-refereed journals. If you are willing to participate in this project, please complete the survey after completing the experiment, and return it to the nominated location indicated by your laboratory supervisor. Please do not hesitate to speak to your laboratory supervisor during the experiment if you have any questions about this study. Thank you for your cooperation.

Who?For questions regarding the ASELL project at Curtin, please contact: Dr Daniel Southam, Project Coordinator Telephone: (08) 9266 7265, Facsimile: (08) 9266 2300, Email [email protected]

Curtin University administers human ethics concerns relating to data collection under the auspices of ASELL. Any person with concerns or complaints about the conduct of this research study at Curtin can contact the Secretary of the Human Research Ethics Committee (phone: 9266 2784 or [email protected] or in writing C/- Office of Research and Development, Curtin University, GPO Box U1987, Perth WA 6845) quoting the following project number: SMEC-50-10.Preface 16

PART 1: PRINCIPLES OF CHEMISTRY AND CHEMICAL MEASUREMENT

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EXPERIMENT 1.1: INTRODUCTION TO THE LABORATORY CHEMICAL PUZZLESSafety

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The chemical hazards in this laboratory a minimal. Your demonstrator will illustrate the procedural hazards during the pre-laboratory briefing. You must wear safety glasses, a laboratory coat and fully enclosed shoes covering your forefoot, toe and heel at all times whilst in the laboratory during this experiment.

IntroductionAs is always the case in the conduct of science, today's tasks are as much about thinking as about doing. You will be given some problems that have a chemical basis. For each problem, there is more than one "correct" solution: indeed there are many valid solutions. Supervisors and demonstrators do not have the answers. There are no recipes. There is no specification of apparatus. We will be looking for: (a) (b) (c) (d) (e) (f) originality of approach validity of logic awareness of assumptions underlying the method used ability to communicate thought processes use of different approaches to the same problem reproducibility of your experiment (i.e. did you attempt it more than once)

There are two purposes to this "laboratory exercise": 1. 2. The problems are inherently interesting. Enrollment in this unit suggests that you want to develop some of the skills of scientists. Scientists are students - students of nature, to be sure, but like students, dependent for their success on the taking of notes. In even the most routine of scientific research, scientists must preserve external records of their work. Most externalise far more than just data: they might include making records of their hypotheses and predictions, "What if ...?" statements, notes from research literature, bright ideas (or wild speculations), plan, attempts to make sense of unexpected observations, and so on.

Your demonstrator will give you five tasks. During the laboratory session, you should do a minimum of at least two of the tasks in-depth. At least one of these should be task 3. The choice is yours. There is no pre-laboratory exercise for this experiment.

Experiment 1.1: An introduction to the laboratory

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Learning OutcomesOn successful completion of this experiment, students will be able to: 1. 2. 3. 4. recognise the various glassware and apparatus available in the Chemistry laboratory, form an aim or hypothesis, test it with an experiment, discuss the results obtained and draw a conclusion, write a brief scientic report using appropriate language. work as a team to achieve complex tasks, communicate within a team.

Report writingEach of the four scenarios must be written as a short mini lab report. There are four headings which are common to most scientific reports. You should write all scientific reports in third person past-tense. Your demonstrator will assist you in developing this skill by showing some examples. The relative length of the space provided will guide you about how much you write.

AimWhat does your experiment hope to achieve? Write two or three sentences using scientific language that describes your experimental aim. This explains to the reader (your demonstrator) what you hoped to achieve.

Experimental ProcedureWrite the experimental procedure exactly as you perform the experiment. This section should be written with enough detail such that any other skilled person could perform the same experiment and achieve the same results.

Results and DiscussionThis section should state your results, or a summary of your results, such as in tables and graphs. Discuss the meaning of the results in the context of the aims of the experiment and state their relevance to the findings of the experiment. Presentation of results without discussion will result in significantly lower marks. As a guide, when you present a result always think what does it mean? and try to communicate this meaning to the reader. This is where your demonstrator will be looking for a description of your individual logical thinking and marking you accordingly.

ConclusionYour conclusion should be brief sentence or two answering the stated aim. Include a brief summary of any relevant results. While you will work in teams, its important to put the report in your own language. If you copy the words from a report submitted by another student this is called plagiarism.

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Plagiarism is taking the ideas or words of someone else and representing them as your own. It is often considered easier just to copy rather than to put the ideas into your own words. However, students who copy or who are copied from are considered to have plagiarised this work and all parties will be reported to the University and may face disciplinary action. See the Academic Integrity website for more details: http://academicintegrity.curtin.edu.au/


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Name

Student ID

Results and discussionThis will be hard work! There are many "correct" answers. The session is as much about thinking and communicating as it is about doing, but all the tasks require experimentation. You should discuss your thoughts, plans and ideas (written up in your laboratory report, of course) with your demonstrator. Problem 1: You are given a piece of sponge.

Task: What percentage of the volume of the sponge is air space?

Aim

Experimental Procedure


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Results and Discussion

Conclusion


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Problem 2:

You are part of an emergency team that must decide whether the Eskimo settlement will be flooded if the icebergs melt.

Task: For a given mass of ice, m, and volume of water, V, with surface area, A, what will be the change of water level, h, when the ice melts?

Aim



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Conclusion


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Problem 3:

You must find the most accurate and precise measure of volume

Task: Using the apparatus available in the laboratory, you must find the piece of equipment that most accurately dispenses 20.00 mL of water the most often using the weight dispensed as the measure of accuracy.

Aim



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Conclusion


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Problem 4:

You are provided with some anti-acid tablets.

Task: Find the volume of gas released when one tablet dissolves in water.

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Conclusion


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Problem 5:

You are given five colourless solutions labelled A, B, C, D and E. One is a 0.5 M hydrochloric acid solution, one is a 0.5 M sodium hydroxide solution, one is a 0.5 M sodium carbonate solution, one is a phenolphthalein solution and one is water.

Task: Using only the above reagents, identify the five solutions.

Aim



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Results and DiscussionThe table below will help you with framing your results (and perhaps your experimental)! A B C D E

A

B

C

D

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Conclusion


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Departure Checklist

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You must complete this checklist before you leave the laboratory. Your demonstrator will initial where indicated when the report is received and will check you have performed each of these tasks.

A two mark deduction from the total mark for this experiment will apply if the checklist is not complete and your demonstrator has not initialed your report. Tick each task as you complete it and ensure your demonstrator has initialed it before you leave the laboratory. Reports without your demonstrators initials will not be marked. My work area is clean and tidy I have cleaned and returned all glassware to the lockers I have wiped down all common areas, such as fumehoods and sinks I have returned all the reagents used I have attached the pre-laboratory questions to my result sheets only. Demonstrators initials

AssessmentYour demonstrator will assess your performance in this laboratory according to this assessment key below. Up to 20% of the mark associated with this lab can come from your demonstrators perspective on your laboratory conduct, including cleanliness and general capability. Criteria Originality of approach, statement of aims provided Validity of logic, experimental procedure stated and valid Communication of the logic underlying the method used, discussion of results Ability to communicate the experiment through writing of a logically structured report Awareness of reproducibility, experiment was repeated and results were comparable Poor 0 0 0 0 0 0.5 0.5 0.5 0.5 0.5 Good 1 1 1 1 1 Excellent 1.5 1.5 1.5 1.5 1.5 2 2 2 2 2

Total (out of 10)


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EXPERIMENT 1.2: DETERMINATION OF ACETIC ACID IN VINEGARSafety

!PPE


Learning OutcomesOn successful completion of this experiment, students will be able to: 1. 2. 3. manipulate volumetric glassware to achieve an accurate and reproducible volumetric analysis, standardise from a hydrochloric acid solution of known concentration a provided sodium hydroxide solution of unknown concentration and calculate its concentration, using this standardised sodium hydroxide solution determine the concentration of acetic acid in a provided sample of vinegar,

Principles of volumetric analysis1. The aim of quantitative analysis is to determine the quantity of a particular species in a given sample. Analysis that depends on measurement of volume is called volumetric analysis. This analysis is carried out by matching a known quantity of a reactant A (the standard) against an unknown quantity of a reactant B (the unknown). For this purpose a solution of one reactant is added progressively to a solution of the other. This process is called titration. Only certain chemical reactions are suitable as a basis for matching reactants in a titration. There are several requirements. (a) (b) (c) (d) (e) 2. There must be some means of knowing when the matching quantity of one reactant has been added to the other. The point where the quantities are matched is called the equivalence point. The reaction must be free from side-reactions so it can be represented by a single equation. The reaction rate should be fast so that the equivalence point can be accurately detected. The reaction must go essentially to completion, i.e. the equilibrium constant for the reaction must be large.

The reactions used in volumetric analysis are of three types. (a) Those dependent on the combination of ions, as in acid-base titrations and precipitation titrations.33

Experiment 1.2: Determination of acetic acid in vinegar

(b) (c) 3.

Those dependent on electron transfer (oxidation-reduction reactions). Those dependent on complex formation.

The technique of volumetric analysis involves the understanding and mastering of the following equipment. (a) (b) (c) (d) The pipette - used in the delivery of accurately known aliquots (volumes) of solution. The burette - used in the technique of titration to dispense and accurately measure the volume of titrant. The balance - weighing of objects on both top-loading and analytical balances. The volumetric flask - used in the preparation of standard solutions of accurately known concentrations.

Each of these techniques will be covered in extensive detail so that students can familiarise themselves with the mastery required in the collection of accurate analytical data.

Using a pipette correctlyThe pipette is used to deliver a known volume, but will only do so if used as follows: (a) (b) (c) (d) Clean the pipette by washing thoroughly with detergent and tap water. Allow the pipette to drain, wash thoroughly with tap water and finally rinse with deionised water. Rinse the pipette two or three times with a small amount of the liquid, tilting to ensure that the whole inner surface is rinsed. Insert the pipette into the a pipette filler with a slight pressure. This assures a secure fit. Never insert the pipette more than 1 cm into the pump.

!(e) (f) (g)

Be careful inserting a pipette into a pipette filler. Always grasp the pipette at wide top, never at or below the bulb, and never apply too much force. One of the most common laboratory injuries is from a pipette filler being inserted with too much force causing cuts or even penetration into hands or arms as a result. Draw up the liquid until it is above the graduation mark. Wipe away any adhering liquid from the outside of the lower stem with a cloth or paper towel. Allow the liquid to drip out slowly until the bottom of the meniscus just reaches the graduation mark. The pipette must be held vertically with the mark at eye level. The meniscus is the rounded top surface of the solution caused by adhesion of the solution to the walls of narrow glass tubes. The base of the meniscus is where all volumetric glassware should be read from.

STOP(h) (i) (j) (k)

Remove any drop adhering to the tip by touching against a glass surface, not by wiping. Allow the liquid to run into the receiving vessel with the tip of the pipette touching the wall of the vessel. Do not allow the tip to be immersed in the liquid. When the continuous discharge has ceased, hold the jet in contact with the side of the vessel for 15 seconds (draining time). The liquid remaining in the jet at the end of the drainage time must not be removed either by blowing or any other means. Pipettes are calibrated to exclude any remaining solution.34


(l)

All pipette volumes should be recorded in one decimal place as 10.0, 20.0, 50.0 mL.

The specifications for pipettes in common use are: Capacity (mL) Tolerance ( mL) (Class B) Delivery Time (secs) (Classes A and B) 10.0 0.04 15-25 20.0 0.05 15-30 50.0 0.08 25-40

How to read a burette accuratelyIt is important that you learn how to read a burette accurately. A well-trained titrator can read a burette to 0.01 mL. In this unit we expect you to be able to read the burette to 0.05 mL and report all volumes accurately. The figure at the right illustrates how this is done by positioning the baseline of the meniscus using the volume marks on the burette. A burette has volume marks at 0.10 mL increments. To read it accurately we look at the meniscus being on or close to the line (.00 mL) or about half way (.05 mL). Note how we still report the 0 when the meniscus is on the line as this digit is significant (e.g. 3.10 mL, 3.40 mL etc). You must write this number down and include the significant figures in the calculations.

3

3.10 mL 3.25 mL 3.40 mL 3.55 mL 3.70 mL 3.80 mL

When reporting the volumes, ensure that you include the value of the number immediately above your meniscus and count down the number of tenth markings, as illustrated above. You must bring your eye level with the meniscus to read this accurately. To do this when looking at the burette marking you should see one continuous line through the glass wall of the burette. If you see two lines you are not at eye level. You will read the burette twice; before your titration for the initial reading which should never be at 0.00 so you have marking above the meniscus to accurately judge its position and then immediately after your titration. Always record the volume of the burette to two decimal places.

Acid-base titrationsA titration is performed by reacting a standard solution with an unknown solution. Either the standard solution, or the solution containing the unknown, is pipetted into a conical flask. The other solution is then added progressively from a burette. Up to the equivalence point the solution contains an excess of one reactant; after the equivalence point it contains an excess of the other reactant. Some means of observing this changeover must be available. In acid-base titrations, the change in colour of an indicator may be used as evidence of the changeover. The observable point in the titration is called the end point. The end point must be as close as possible to the equivalence point; to achieve this the indicator must be carefully selected.Experiment 1.2: Determination of acetic acid in vinegar 35

Steps involved in a simple acid-base titration procedure: e.g. Sodium hydroxide (NaOH) versus hydrochloric acid (HCl)1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. Clean and rinse with deionised water two 250 mL beakers and three 250 mL conical flasks into which samples will be placed. Rinse one beaker with a small amount of the HCl solution to be taken and label accordingly. Pour the required amount of HCl into the beaker. Rinse the other beaker with a small amount of the NaOH solution to be taken and label accordingly. Pour the required amount of NaOH into the beaker. Rinse the pipette with the HCl. Fill the pipette with the HCl and deliver the 20.0 mL into the previously washed flask from (1). Add 2 or 3 drops of the appropriate indicator to the HCl. Do not add more than the specified amount. Repeat steps (7) and (8) for two or more further conical flasks as required. Clean and rinse a burette. Check for free running of the tap. With a ground glass tap ensure there is no excess grease. Rinse the burette with the NaOH solution. Mount the burette on a retort stand using a burette clamp and adjust the height of the burette such that the tip height is below the mouth of the 250 mL conical flask. Fill the burette with NaOH using a small plastic funnel. Close the tap before filling and remove funnel before commencing the titration. Run a few mL of NaOH out the tap of the burette to force the air out of the tip. Touch the tip of the burette against a wall of the waste beaker to remove any excess NaOH. Place a piece of white paper beneath the conical flask. This will assist you in detecting indicator colour changes. Record the initial volume to two decimal places. Holding the burette tap in your left hand and swirling the conical flask with your right hand titrate the HCl until the first colour change is noted. Ensure all splashings, etc. are washed down into the bulk solution. Record the final volume to two decimal places. Carry out a blank titration if necessary. Repeat this procedure until titration readings agree to within the tolerance required for the particular titration.

17. 18.


36

Part 1: Standardisation of an approximate 0.1 M sodium hydroxide solutionTitrations require the concentration of at least one component to be accurately known. The process of obtaining the concentration is called standardisation, and in part 1 we will standardise an approximate 0.1 M solution of sodium hydroxide (NaOH) using a known concentration of hydrochloric acid (HCl) that will be around 0.1 M (the accurate concentration will be provided by your demonstrator). These two will react together such that every 1 mole of HCl will react with 1 mole of NaOH in the following reaction: NaOH (aq) + HCl (aq) H2O (l) + NaCl (aq) Sodium hydroxide is not a good standard reagent because it will react slowly over time with carbon dioxide in the air to produce sodium carbonate, and therefore must be regularly standardised.

ProcedurePipette three 20.0 mL aliquots of the HCl solution into three clean conical flasks, and add 2 3 drops of methyl red to each. Titrate the first solution to obtain a rough volume of titrant required and then carry out consecutive titrations until your results are within 0.10 mL of each other. Leave the burette with the NaOH solution for Part 2.

STOP

Read the burette to 0.05 mL. If youre not sure how, ask your demonstrator!

Part 2: Determination of acetic acid in vinegarNow we have a standardised sodium hydroxide, we can use this to determine the concentration of acetic acid in vinegar. Acetic acid is our analyte in our sample of vinegar and it will react with sodium hydroxide in a 1:1 reaction as we saw in part 1. CH3COOH (aq) + NaOH (aq) H2O (l) + NaCl (aq)

Procedure

STOP

Your sample of commercial vinegar has been diluted 7 times. Make sure you include this when calculating the final concentration in the original vinegar.

Pipette three 20.0 mL aliquots of the vinegar solution into three clean conical flasks and add 2 drops of phenolphthalein indicator to each. Titrate these solutions with the standardised sodium hydroxide solution from Part 1. The end point is shown when the indicator changes from colourless to pink. Express your result as moles of acetic acid per litre the commercial vinegar to one decimal place. Clean your burette thoroughly after use.


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38

Name

Student ID

Pre-laboratory questions: Acid-base titrations1. Why should the pipette be rinsed with NaOH (and the burette with HCl) prior to their use in dispensing these solutions?

2.

Can the NaOH solution be blown out of the pipette to reduce the time for the transfer? Briefly explain.

3.

Why should a constant, minimum amount of indicator be used in titrations?


39

4.

Calculate what volume of 0.100 M NaOH would you expect to deliver from the burette to standardise 20.00 mL of 0.102 M HCl?

5.

Assume that you will be carrying out four titrations using 20.0 mL of 0.1 M HCl. Approximately what volume of NaOH should you require?

Submit this sheet to your demonstrator when you enter the laboratory at the start of the session.Experiment 1.2: Determination of acetic acid in vinegar 40

Name

Student ID

Part 1: Standardisation of approximately 0.1 M NaOHConcentration of provided HCl (see the carboy in the laboratory and write this value down here)

TitrationsBurette Readings (mL) Final Initial Titre Rough Titration

mol L1

Accurate Titrations Place an asterisk next to your concordant results

Mean titre volume of your concordant results Determine the accurate concentration of NaOH, showing all working clearly. If required, determine the error in this value using the procedure given in the preface of your laboratory manual. You may attach additional sheets if necessary.

mL

Concentration of NaOH (to three decimal places)


mol L141

Part 2: Determination of acetic acid in vinegarConcentration of NaOH (from part 1)

TitrationsBurette Readings (mL) Final Initial Titre Rough Titration

mol L1

Accurate Titrations Place an asterisk next to your concordant results

Mean titre volume of your concordant results

mL

Determine the concentration of acetic acid in the undilute vinegar in moles per litre, showing your working clearly. If required, determine the error in this value using the procedure given in the preface of your laboratory manual. You may attach additional sheets if necessary.

Concentration of acetic acid in undiluted commercial vinegar (to three decimal places) taking into account that the sample provided was diluted before analysis.


mol L142

Departure Checklist

STOP



AssessmentYour demonstrator will assess your performance in this laboratory according to this assessment key below. Up to 20% of the mark associated with this lab can come from your demonstrators perspective on your laboratory conduct, including cleanliness and general capability.Criteria Pre-laboratory questions were...0 Not attempted 0.5 Poorly attempted 1 Mostly incorrect 1.5 Mostly correct 0 No 2 Complete and mostly correct 0 No 2 Complete and mostly correct 2 All correct 1 Yes 3 Complete and fully correct 1 Yes 3 Complete and fully correct

Part 1: Concordant titre values with appropriate number of significant figures were provided Part 1: Calculations from the concordant results were...0 Not attempted 0.5 Incomplete or partially attempted 1 Complete but incorrect

Part 2: Concordant titre values with appropriate number of significant figures were provided Part 2: Calculations from the concordant results were...0 Not attempted 0.5 Incomplete or partially attempted 1 Complete but incorrect

Total (out of 10)


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44

EXPERIMENT 1.3: STANDARDISATION OF HYDROCHLORIC ACID WITH BORAXLearning OutcomesOn successful completion of this experiment, students will be able to: 1. 2. 3. recognise a primary standard, use a solid to standardise an unknown concentration of a solution and, master skills in weighing by difference, analytical transfer of solids and titration.

AimTo utilise a standard solution of known concentration to determine the unknown concentration of a hydrochloric acid solution.

IntroductionAs we discovered in experiment 1.2, it is necessary to standardise sodium hydroxide regularly due to constant reaction with atmospheric carbon dioxide reducing the concentration of hydroxide present in solution. To do this in experiment 1.2 we used a standardised hydrochloric acid solution. But how was the hydrochloric acid standardised? In this experiment we will standardise a solution of approximately 0.1 M hydrochloric acid. Solutions are standardised against substances known as primary standards, which should have the following desirable properties. 1. 2. Be readily preserved in a pure state and easy to dry. Must not be hygroscopic or efflorescent, i.e. must not alter in weight during weighing or vary in composition due to reaction with atmospheric gases, such as moisture or carbon dioxide. Have a high molecular weight so that weighing uncertainties are minimised. Be readily soluble under the conditions being employed. Must react stoichiometrically with the substance being standardised.

3. 4. 5.

Certain solutions when standardised may be used as standards themselves. These are known as secondary standards, e.g. HCl. In this experiment we will use borax or sodium tetraborate decahydrate, Na2B4O710H2O, as our primary standard. This will react with an acid, such as hydrochloric acid, according to the following reaction. Na2B4O7 (aq) + 2HCl (aq) + 5H2O (l) 4H3BO3 (aq) + 2NaCl (aq)

Therefore, the reaction between the tetraborate ion and hydrochloric acid has a molar ratio of 1:2 respectively.

Experiment 1.3: Standardisation of hydrochloric acid with borax

45

ProcedureAccurately weigh three samples of the required weight of borax directly into three clean 250 mL conical flasks using the following procedure. 1. 2. Place a clean dry weighing bottle onto a tared (zeroed) balance. Never tare (zero) the balance with the empty container on the pan. Remove the weighing bottle and weigh out approximately the required amount of the primary standard. Never weigh reagents into a container while it is still on the balance. Record the mass of the weighing bottle plus borax. Transfer the contents of the weighing bottle to a clean 250 mL conical flask, ensuring that you do not lose any of the borax. Re-weigh the weighing bottle containing any residue of the substance that did not come out in the transfer stage in 3 above and record the weight. By subtraction, the weight of substance transferred can be accurately determined. Ensure you clean the weighing bottle before your next measurement.

3. 4.

Dissolve the borax in about 100mL of deionised water. It is not necessary to know accurately the volume of water as we know the mass present in the flask and from this can determine the number of moles of the tetraborate ion present. Add three drops of methyl red indicator and titrate against the approximately 0.1 M solution of hydrochloric acid. Repeat the titration twice more. As it is unlikely that you will get exactly the same mass of borax three times, a quick check for concordance of your results is to divide the titre volume by the mass of borax present. Your results should be 0.10 mL g1. Calculate the concentration of hydrochloric acid accurately for each of the three borax titrations, not forgetting that for every one mole of tetraborate present two moles of hydrochloric acid will react. In this procedure we will also begin to examine the uncertainty associated with volumetric analysis. When calculating your concentration of hydrochloric acid, also calculate the uncertainty in this measurement by considering the tolerances of the volumetric glassware and balances used.

STOP

See pages 13 15 of this lab manual for a simple method for calculation of uncertainties.


46

Name

Student ID

Pre-laboratory questions: Standardisation of hydrochloric acid with borax1. Calculate the weight of borax required to give a titre of 20.00 mL with 0.1 M HCl. Borax is sodium tetraborate decahydrate (Na2B4O710H2O) and we will use the analytical reagent (AR) grade, which we can assume is 99.9% pure. This will be the mass you will require to give a reasonable titre value in this experiment.

2.

Is it necessary to accurately measure the 100 mL of deionised water used to dissolve the borax? Briefly explain.


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48

Name

Student ID

Results: Standardisation of hydrochloric acid with boraxWeighings (g) Wt weighing bottle + borax Wt weighing bottle Wt borax Burette Readings (mL) Final Initial Titre Quick check for concordance, if the ratios are close then we have accurate titre values Ratio 1 2 3 1 2 3 1 2 3

Calculate the concentration of HCl, including uncertainties, in three titrationsTitration 1


49

Titration 2

Titration 3

Concentration of HCl Titration 1 Titration 2 Titration 3 Average concentration M M M M


50

Departure ChecklistA two mark deduction from the total mark for this experiment will apply if the checklist is not complete and your demonstrator has not initialed your report. Tick each task as you complete it and ensure your demonstrator has initialed it before you leave the laboratory. Reports without your demonstrators initials will not be marked. My work area is clean and tidy I have cleaned and returned all glassware to the lockers I have wiped down all common areas, such as fumehoods and sinks I have returned all the reagents used I have attached the pre-laboratory questions to my result sheets only. Demonstrators initials

AssessmentYour demonstrator will assess your performance in this laboratory according to the assessment key below. Up to 20% of the mark associated with this lab can come from your demonstrators perspective on your laboratory conduct, including cleanliness and general capability.Criteria 0 Pre-laboratory questions were... Concordant titre values with values given to 1 mL per gram of borax... Concentration of HCl calculate correctly, including uncertainty... Accuracy of calculated HCl concentration compared to expected value...Not attempted

0.5Poorly attempted

1Mostly incorrect

1.5Mostly correct

2All correct

0No

1Sometimes

2Always

0No

1Partially

2Completely

0 20%

1 15%

2 10%

3 5%

4 2%

Total (out of 10)


51



52

EXPERIMENT 1.4: STANDARDISATION OF HYDROCHLORIC ACID WITH A STANDARD SOLUTION OF SODIUM CARBONATESafety

!PPE


Learning OutcomesOn successful completion of this experiment, students will be able to: 1. 2. 3. 4. weigh accurately by difference, transfer a solid quantitatively, prepare a solution of known concentration and, use this solution titrimetrically to quantify the unknown concentration of an solution.

AimTo utilise a standard solution of known concentration to determine the unknown concentration of a hydrochloric acid solution.

IntroductionA solution of a primary standard can be used in exactly the same way it was used experiment 1.3. A solution of the primary standard may be preferable to using the solid directly if this solid is likely to change over time due to atmospheric moisture. To prepare a standard solution we must know the accurate mass of our primary standard, which is then dissolved in deionised water and transferred to a volumetric flask and made to the volume. To make a solution accurately we must use a volumetric flask. This piece of glassware has an accurately known volume and typically they are found in sizes from 1.000 mL up to 10.0 L. Today we will use a 250.0 mL flask with a tolerance of 0.5 mL. By transferring a solution containing a known mass of a primary standard (and therefore a known number of moles) we can make the flask to volume and it will have an accurately known concentration. To make the flask to volume we must fill it carefully to the mark with our solvent, usually deionised water. To do this fill with a wash bottle until the solvent is at the base of the neck then add your solvent dropwise with a pasteur pipette (not aExperiment 1.4: Standardisation of hydrochloric acid with a standard solution of sodium carbonate 53

volumetric pipette) until the base of the meniscus is at the etched volume mark. You cannot remove solvent if you go over the mark accidentally, so be careful at this step, otherwise you must start again.

ProcedureIn pairs prepare 250.0 mL of an approximately 1 0.05 M solution of sodium carbonate using the following procedure. 1. 2. Place a clean dry weighing bottle onto a tared (zeroed) balance. Never tare (zero) the balance with the empty container on the pan. Remove the weighing bottle and weigh out approximately the required amount of the primary standard. Never weigh reagents into a container while it is still on the balance. Record the mass of the weighing bottle plus sodium carbonate. Transfer the contents of the weighing bottle to a clean 250 mL beaker, ensuring that you do not lose any of the sodium carbonate. Re-weigh the weighing bottle containing any residue of the substance that did not come out in the transfer stage in 3 above and record the weight. By subtraction, the weight of substance transferred can be accurately determined. Dissolve the solid in 50 mL of deionised water. Transfer the solution from the beaker to a clean 250.0 mL volumetric flask using a small filter funnel to facilitate transfer. Wash the beaker thoroughly with deionised water and transfer the washings to the volumetric flask. Wash the filter funnel with a little deionised water and then remove from the volumetric flask. Using deionised water make up the solution in the flask until the bottom of the meniscus is level with the graduation mark, as illustrated in figure. Finally stopper the flask firmly and shake thoroughly, inverting several times to aid mixing.

3. 4.

5. 6. 7. 8. 9.

Individually transfer approximately 100 mL of the sodium carbonate solution into a clean and dry beaker and pipette three 20.0 mL aliquots of the standard sodium carbonate solution into clean conical flasks. Dilute each to about 60 mL with water 2. Add three drops of methyl orange-indigo carmine indicator and titrate with the hydrochloric acid until the indicator turns grey. The end point has been overstepped if a magenta colour develops. Sodium carbonate will react with an acid, such as hydrochloric acid, according to the following reaction. Na2CO3 (aq) + 2HCl (aq) 2NaCl (aq) + CO2 (g) + H2O (l)

Therefore, the reaction between the carbonate ion and hydrochloric acid has a molar ratio of 1:2 respectively.

STOP

See the preface of this lab manual for a simple method for calculation of uncertainties.

1

You are unlikely to get exactly the correct mass to obtain exactly 0.0500 M sodium carbonate solution, but it will still be accurately known, typically within three signicant gures. It doesnt matter whether you have 0.0512 M or 0.0474 M, so long as you use your accurately known concentration in your calculations. It is not necessary to note how much deionised water you add, as the only source of sodium carbonate should be from the standard solution. 54

2

Experiment 1.4: Standardisation of hydrochloric acid with a standard solution of sodium carbonate

Name

Student ID

Pre-laboratory questions: Standardisation of hydrochloric acid with a standard solution of sodium carbonate1. Calculate the weight of anhydrous AR sodium carbonate (Na2CO3) required to make 250.0 mL of 0.0500 M solution. This will be the mass you will require to give a reasonable titre value in this experiment.

2.

Why should all solid be dissolved before transfer of the solution from the 250 mL beaker to the volumetric flask?

3.

Why is it necessary to shake the volumetric flask thoroughly after the solution has been made up to the mark?


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56

Name

Student ID

Results: Standardisation of hydrochloric acid with a standard solution of sodium carbonatePart 1: Preparation of a standard 0.05 M solution of sodium carbonateWeighings (g) Wt weighing bottle + Na2CO3 Wt weighing bottle Wt Na2CO3

Calculate the concentration of anhydrous sodium carbonate including uncertainties

Concentration of sodium carbonate

M57


Part 2: Titration of sodium carbonate against hydrochloric acidBurette Readings (mL) Final Initial Titre Mean titre volume mL Rough Titration Accurate Titrations

Calculate the concentration of HCl including uncertaintiesRecall that every one mole of sodium carbonate reacts with two moles of hydrochloric acid.

Concentration of hydrochloric acid

M58


Departure ChecklistA two mark deduction from the total mark for this experiment will apply if the checklist is not complete and your demonstrator has not initialed your report. Tick each task as you complete it and ensure your demonstrator has initialed it before you leave the laboratory. Reports without your demonstrators initials will not be marked. My work area is clean and tidy I have cleaned and returned all glassware to the lockers I have wiped down all common areas, such as fumehoods and sinks I have returned all the reagents used I have attached the pre-laboratory questions to my result sheets only. Demonstrators initials

AssessmentYour demonstrator will assess your performance in this laboratory according to the assessment key below. Up to 20% of the mark associated with this lab can come from your demonstrators perspective on your laboratory conduct, including cleanliness and general capability.Criteria 0 Pre-laboratory questions were... Concentration of Na2CO3 calculated correctly, including uncertainty... Concordant titre values with values given to 0.05 mL... Concentration of HCl calculated correctly, including uncertainty... Accuracy of calculated HCl concentration compared to expected value...Not attempted

0.5Poorly attempted

1Mostly incorrect

1.5Mostly correct

2All correct

0No

1Partially

2Completely

0No

1Sometimes

2Always

0No

1Partially

2Completely

0 20%

0.5 15%

1 10%

1.5 5%

2 2%

Total (out of 10)


59



60

EXPERIMENT 1.5: AN INTRODUCTION TO ORGANIC CHEMISTRYSafety

!PPE

Many of the substances used in this experiment are flammable. Please use them in the fumehood and ensure there are no sources of ignition. Sodium must be kept out of contact with water. It is also highly corrosive. Do not let it come into contact with your skin. Dispose of excess sodium by reacting it completely in ethanol and pouring the solution into the waste beaker in the fumehood. You must wear safety glasses, a laboratory coat and fully enclosed shoes covering your forefoot, toe and heel at all times whilst in the laboratory during this experiment. This includes when using molecular models.

Learning OutcomesOn successful completion of this experiment, students will be able to: 1. 2. 3. visualise the three-dimensional structure of some simple hydrocarbons using a molecular model kit, represent the three-dimensional structure using conventional two-dimensional notation and, observe some characteristic reactions of four common functional groups.

AimTo observe representations of the three-dimensional structures of some simple hydrocarbons using a molecular modeling kit. To explore the characteristic reactions of some common organic functional groups.

IntroductionOrganic Chemistry is the study of hydrocarbons and their derivatives. Hydrocarbons are compounds made up of carbon and hydrogen. Hydrocarbons can be saturated and unsaturated. Derivatives can contain elements other than carbon and hydrogen, such as oxygen, nitrogen, sulfur, phosphorus and the halogens (group 17 elements). Here are some examples of names of alkanes and cycloalkanes. Look carefully at these so that you can work out how the different styles of representing these molecules are used, and how to translate from one style to another.

Experiment 1.5: An introduction to organic chemistry

61

Name methane ethane propane butane pentane hexane

Condensed formula CH4 CH3CH3 CH3CH2CH3 CH3CH2CH2CH3 or CH3(CH2)2CH3 CH3CH2CH2CH2CH3 or CH3(CH2)3CH3 CH3CH2CH2CH2CH2CH3 or CH3(CH2)4CH3

Structural formula CH4 CH3CH3 CH3CH2CH3 or CH3CH2CH2CH3 or CH3CH2CH2CH2CH3 or CH3CH2CH2CH2CH2CH3 or

cyclohexane

C6H12 or

The molecules obviously do not exist in two dimensions as represented on the two-dimensional paper. Nor are most molecules locked into a single fixed shape. There is free rotation about many covalent bonds and of the molecules listed above, only one has a single shape. The C atom is always tetravalent (it forms four covalent bonds with neighbouring atoms). Bearing in mind the constant covalence of C and the importance of atomic sequence, examine the next set of examples. Notice that although 1,1-dichloroethane is represented in six different forms (more are possible), you should recognise that each represents the same molecule.

1,1-dichloroethane

or

or

or

or Cl2CHCH3 or CH3CHCl2

Part 1: Molecular modelsIn the first part of the experiment today, we will use molecular models to represent the structure of organic molecules. An appreciation of the three-dimensional arrangement of atoms in molecules is important in order to rationalise and understand many of the physical and chemical properties of organic compounds. In this exercise you are asked to: (i) (ii) (iii) construct models of a number of simple molecules draw a reasonable three-dimensional representation of the resulting structures answer some questions regarding these structures

The FlexibleStereoChemistry model kit utilises lengths of plastic tubing to represent chemical bonds. While this is useful for many purposes, the models do not give a good indication of the effective size of atoms or groups of atoms. Space-filling models are required for that purpose.Experiment 1.5: An introduction to organic chemistry 62

Part 2: What is organic chemistry? An exploration of functional groupsA functional group is the component of an organic molecule that gives it its characteristic reactivity or function. This experiment involves some of the fundamental reactions of the common functional groups. It also includes the formation, on test tube scale, of crystalline derivatives characteristic of a particular functional group. Students are expected to regard every test as an investigation and through this develop an awareness of the correlation between structure and reactivity. Write equations for every reaction. The functional groups we will examine in this experiment have the following general formulae, where R is any hydrocarbon chain or ring. Name General Formula Example methanol CH3OH Alcohols and phenols phenolOH

R

OH

OAldehydes

propanal O

C R O H

H3C C H2

C H

propanone O

Ketones

C R R'H3C

C CH3

STOP

The procedure for todays experiment is included with your report sheet.


63



64

Name

Student ID

Pre-laboratory questions: An introduction to organic chemistryDraw structural formulas or unambiguous condensed structural formulas for each of the following: (a) octane

(b)

decane

(c)

cyclobutane

(d)

cyclopentane

(e)

methylcyclobutane

(f)

1,1-dimethylcyclobutane

(g)

2-bromo-1-chlorobutane

(h)

1-bromo-2-chlorocyclobutane (two isomers)


65

Complete the following table for some of the reagents you will be using today. Common name Structure IUPAC name

methyl alcohol

ethyl alcohol

n-butyl alcohol

sec-butyl alcohol

tert-butyl alcohol

formaldehyde

benzaldehyde

acetone

acetaldehyde

cyclohexanone


66

Name

Student ID

Part 1: Procedure and results

STOP

Before you commence Part 1, read Part 2 thoroughly. You do not need to complete this experiment in sequence. Make sure to manage your time effectively.

Construct a model of methane, CH4, by clicking together two pieces of black tubing to create a tetrahedral carbon atom. Place a white ball on each "bond" to represent H atoms. Note the equivalence of all four bonds, i.e. of all four hydrogen atoms. 1. What is the HCH bond angle in methane? Draw a diagram representing this structure.

Make a model of ethane, CH3CH3. Note that rotation about the CC bond can lead to an infinite number of arrangements of the six hydrogen atoms, i.e. an infinite number of conformations. 2. What is the HCH bond angle in ethane? Draw a diagram representing this structure.

Make a model of ethylene (ethene), CH2=CH2, using two trigonal carbon atoms (grey). Note that the double bond prevents rotation about the axis joining the two bonded atoms. 3. What is the HCH bond angle in ethylene? Draw a diagram representing this structure.


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4.

You cant make a model of acetylene, CHCH, as there is no triple bond in the set. Assuming a linear molecule draw a diagram representing the structure of acetylene.

5.

Make a model of both isomers of 1,2-dichloroethylene (ClCH=CHCl). Draw them and identify which is cis and which is trans.

6.

Make a model of 1,2-dichloroethane and draw it. Are there cis / trans isomers possible? Explain.

7.

Draw the structure of 1,2-dichloroacetylene. Are there cis / trans isomers possible?


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8.

Construct a model of cyclobutane. Note that the four carbon atoms are constrained to be essentially coplanar. Cyclopropane, the smallest cycloalkane, is highly strained and it is difficult to construct with the present model kit without causing damage to the plastic tubing. Draw a diagram representing the structure of cyclobutane. Is free rotation around the C C bonds possible?

9.

Make models of the five possible isomeric dimethylcyclobutanes. Draw the structures of the these and name them.

10.

Attach four different coloured balls to a tetrahedral carbon atom (to represent, say, CHFClBr) to generate structure A. Place this structure on the bench and construct structure B that is the mirror image of A. Are structures A and B the same, i.e. are they superimposable? Draw each structure.

If they are superimposable, then they are identical. If they are not superimposable, then they are isomers known as enantiomers. Enantiomers belong to the class of isomers known as stereoisomers and give rise to a special sort of isomerism known as optical isomerism. Stereoisomers have the same atom connectivity but have a different arrangement in space. Your hands exhibit the same phenomenon, where your hands are mirror images but they are not the same.


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Part 2: Procedure and resultsReactions of alcohols and phenolsReaction with sodium

!1.

Sodium must be kept out of contact with water. It is also highly corrosive. Do not let it come into contact with your skin. Dispose of excess sodium by reacting it completely in ethanol and pouring the solution into the waste beaker in the fumehood.

Place a small piece (rice grain size) of clean sodium in 0.5-1 mL of an alcohol in a test tube. What is the gas evolved? How would you test for it?

When the sodium is completely reacted divide the solution into two. Allow one portion to evaporate on a watch glass. 2. What is the residue?

Test the second portion with 2-3 drops of Universal Indicator. Colour observed pH 3. What are the equations for the reactions above?


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Reaction with iron(III) chloride To 0.5 mL of ethanol add 2-3 drops of iron(III) chloride solution. Repeat the experiment using 0.5 mL of 2% phenol solution. Note any colour change.

4.

What do you conclude from these experiments?

Oxidation of alcohols Compare the action of an oxidant, potassium dichromate, on n-butyl alcohol, sec-butyl alcohol, and tert-butyl alcohol. Place three test tubes side by side, each containing five drops of one of the alcohols. To each add 2 drops of acidified potassium dichromate solution and shake. Record your observations. Alcohol n-butyl alcohol Observations

sec-butyl alcohol

tert-butyl alcohol 5. How does the structure of the alcohol affect its ability to be oxidised?


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Reactions of aldehydes and ketonesSilver mirror test Rinse a large test tube with 1 mL of 3 M sodium hydroxide. Place 2 mL of silver nitrate solution. Add 3 M ammonia solution drop by drop until the precipitate first formed just redissolves. To 0.5 mL of this solution in a small test tube, add 1 drop of each reagent from the table. Record in the table what you observe at room temperature and on warming in hot water. Reagent Observations

formaldehyde

benzaldehyde

acetone

Fehling's Solution Prepare a stock of Fehlings solution in a large test tube as follows. To 2 mL of Solution A, containing copper sulfate, add solution B, containing potassium sodium tartrate and sodium hydroxide, until the blue precipitate formed just dissolves to obtain a clear dark blue solution. To 1 mL of this prepared solution in a small test tube, add 3 drops of each reagent from the table. Record in the table what you observe at room temperature and on warming in hot water. Reagent Observations

formaldehyde

acetaldehyde

acetone


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Schiffs reagent To 0.5 mL of Schiff's Reagent (aqueous rosaniline hydrochloride decolourised with sulfur dioxide) add 3 drops of formaldehyde and observe the colour immediately produced. Repeat the test with acetone, benzaldehyde and cyclohexanone. Reagent Observations

formaldehyde

acetone

benzaldehyde

cyclohexanone

Condensation with 2,4-dinitrophenylhydrazine (Brady's Reagent) To 0.5 mL of Brady's Reagent A in a test tube add 2-3 drops of acetone. Warm the test tube gently and allow to cool. If necessary, scratch the inside of the test tube with a glass rod to promote crystallisation. Repeat the test with acetaldehyde, and, using Reagent B, cyclohexanone and benzaldehyde. Reagent Observations

acetone

cyclohexanone

acetaldehyde

benzaldehyde


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Departure Checklist

STOP



AssessmentYour demonstrator will assess your performance in this laboratory according to the assessment key below. Up to 20% of the mark associated with this lab can come from your demonstrators perspective on your laboratory conduct, including cleanliness and general capability.Criteria Pre-laboratory questions were... Part 1: Correct structures and diagrams were provided Part 2: Detailed observations were... Part 2: Correct reactions of selected observed reactions were provided... In-laboratory questions were... Poor 0Not attempted

Good 0.5Poorly attempted

Excellent 1.5Mostly correct

1Mostly incorrect

2All correct

0Not attempted

0.5Poorly attempted

1Mostly incorrect

1.5Mostly correct

2All correct

0Not provided

0.5Very poor

1Adequate

1.5Good

2Excellent

0Not provided

0.5Rarely

0.5Sometimes

1.5Often

2Always

0Not attempted

0.5Poorly attempted

1Mostly incorrect

1.5Mostly correct

2All correct

Total (out of 10)


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PART 2: CHEMISTRY OF THE ELEMENTS

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EXPERIMENT 2.1: IDENTIFICATION OF COMMON IONS IN SOLUTIONSafety

!PPE


Learning OutcomesOn successful completion of this experiment, students will be able to: 1. 2. 3. 4. give accurate and detailed observations, draw logical and relevant inferences, relate the theory to experimental observations, balance chemical reactions.

IntroductionWhen a chemical reaction occurs, substances called reactants are transformed into different substances called products that may have different appearances and different properties. Often you can follow these changes with your own eyes. Learning the skill of making accurate observations is absolutely essential for a scientist. You are going to observe a number of chemical reactions in this laboratory experiment. You must write down your observations, try to draw conclusions based on your observations, figure out what chemical change took place, and express this change in the form of a balanced chemical equation. In this experiment you need to concentrate on writing the correct chemical formulae for all the reactants and products in each reaction. When you write an equation, make sure also that the correct physical state of each substance is designated (g for gas, l for liquid, s for solid, or aq for aqueous species). You must also check each chemical equation to confirm that it is balanced (i.e. it obeys the Law of Conservation of Mass). Common polyatomic ions are detailed in the following table. You should remember the common atomic ions formed. For example, the halogens (F, Cl, Br, I) form halide ions of charge 1 (F, Cl, Br, I), hydrogen forms a H+ cation, and Group 1 metals form +1 cations.

Experiment 2.1: Identication of common ions in solution

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Name Ammonium Acetate Bicarbonate (hydrogen carbonate) Bisulfate (hydrogen sulfate) Bisulfite (hydrogen sulfite) Carbonate Chlorate Chlorite Chromate Cyanide Dichromate Dihydrogen phosphate

Formula Name NH4+

Formula HPO

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