investigations in chemistry -...

Investigations in Chemistry – 2nd edition 0

Investigations

in Chemistry

Support Pack

2nd Edition


Problem Solving Investigations

“Learning about science involves learning about how scientific knowledge is built up

and how scientists collect and use evidence to support their ideas. Pupils not only

have to know about this, they themselves also have to be able to put this learning into

practice by carrying out investigations, collecting evidence, analysing it and

evaluating the strength of it”.

(Frost, 2010, p. 196)

Investigations play an important part in scientific research. Our students need to get a ‘feel’ of

what it entails to undertake an investigation whilst studying Chemistry at SEC level. This type

of activity promotes creative scientific thinking as it encourages students to examine different

possibilities of approaching an investigation. It also provides students with an opportunity to

develop manipulative skills, whilst enhancing accuracy and precision in their approach. This

Support Pack is intended to provide guidelines on how to tackle investigations, how students

should present their write–ups and includes examples of investigations that can be carried

out at various levels.

The first edition of this support pack was written and compiled by Mr. J. Evans (Head of

Department for Chemistry in State schools) and Ms. D. Mizzi (Head of Department for

Chemistry in Church Schools) in 2007. It was distributed amongst Chemistry teachers to

support them during the conduction of Problem Solving Investigations in Chemistry. Further

material and exemplars of students’ work have been included in this second edition of the

support pack to provide the necessary background and assistance.

I would like to thank Mr. J. Evans for the time invested in discussing and developing ideas and

activities whilst compiling and writing the first edition of the booklet. I would also like to

thank the Chemistry teachers for providing examples of investigations and the students at my

school who gave consent to publish their work in this booklet.

Ms. D. Mizzi

Head of Department – Chemistry

Secretariat for Catholic Education

November 2012


1.1 Guidelines for Teachers

Investigations involve an open-ended approach to practical work. Investigations can be

defined as “a task for which the pupil cannot immediately see an answer or recall a routine

method for finding it” (Gott & Duggan, 1995, p.42). The main aim is to encourage students to

ask questions, put forward their tentative ideas and suggestions and develop investigative

skills. Such skills need to be promoted even during routine practical work. Investigations

provide contexts for students to use their existing knowledge and understanding to arrive at

solutions to problems.

An investigation involves four main stages and skill areas, which are discussed in detail in

section 1.3. These include:

planning the investigation

carrying out the investigation and collecting evidence

analysing evidence and drawing a conclusion

evaluating the investigation.

Once students are given a problem to be investigated, class and/or group discussions are

essential in preparing for this type of activity. Investigations involve inquiry and exploration

in which students cannot immediately see an answer or recall a routine method for finding

the solution. During the planning stage, the teacher directs questions without giving specific

answers to help students explore various possible avenues for investigation. Students tend to

encounter difficulties in writing a detailed plan for the investigation. At the planning stage a

basic plan is submitted as explained in section 1.3.1. It is good practice for students to be

given the opportunity to try to make a few measurements or observations to get a ‘feel’ for the

experiment before students hand in a detailed plan. Investigations are fluid in their approach,

and even as the investigation progresses it becomes possible to review what has been

achieved and modify the procedure accordingly. On completing the investigation, follow up

discussions are necessary to help students analyse the obtained evidence, draw relevant

conclusions and evaluate their work.


1.2 Objectives and Learning Outcomes of Investigative Practicals

Objectives of Investigative Practicals Learning Outcomes of Investigative Practicals

to broaden students understanding of the

nature of scientific enquiry.

to provide students with the opportunity to

carry out their own investigations in a

scientific way.

to develop thinking skills through science.

to guide students to carry out preliminary

work in order to acquire and use information

from secondary sources.

to encourage students to use scientific

knowledge and understanding to formulate

ideas and devise an appropriate strategy for

carrying out an investigation.

to improve observational skills and

encourage students to ask relevant questions

about the observations.

to learn how to handle and interpret a variety

of data without guidance from others.

to develop communication skills in

expressing ideas and presenting findings.

to develop the ability for independent

learning through critical analysis and

evaluation.

to prepare students as future citizens and

encourage lifelong learning.

Through investigations Chemistry students will be able to: put forward their ideas and design a way of

investigating a problem.

learn to make predictions of what may happen

during the investigation.

think of variable(s) which can affect the outcome

of the investigation.

decide which variables to keep constant and

which are the ones to be changed.

plan a sequence of practical steps to follow during

the investigation.

select the appropriate apparatus and justify its

choice.

decide on how many readings need to be taken

and what range they should cover.

plan fair tests.

take into account safety measures while handling

chemicals and equipment.

handle equipment and chemicals correctly and

with skill.

make observations carefully and take sufficient

readings with a certain degree of precision.

repeat measurements to ensure reliability.

record evidence clearly and appropriately as they

carry out their work.

plot graphs and interpret them.

identify trends and patterns in the results

obtained.

use evidence obtained to draw conclusions.

decide whether the results obtained support the

original prediction.

explain their conclusions in the light of their

knowledge and understanding of Chemistry.

consider whether the evidence obtained was

sufficient to enable firm conclusions to be drawn.

explain anomalies in observations or

measurements.

evaluate their own work and consider

improvements to the methods followed.


Planning the investigation

Carrying out the experiment and collecting evidence

Analysis of evidence and drawing conclusions

Evaluating the investigation

1.3 Skill Areas in Investigations

Investigations require the drawing together of skills in planning, collecting data, interpreting

data and evaluation. Hence investigations consist of four stages which include:

1.3.1 Planning the Investigation

The initial stage of the investigation involves formulating the first ideas in deciding how to

approach the investigation. Students will share their ideas and discuss a possible strategy

that they are going to follow. This may or may not be based on prior scientific knowledge. At

this stage, students are encouraged to consult secondary sources (e.g. books, internet, etc). In

the planning stage, students will select the apparatus needed, justify its choice and indicate

the procedure to be adopted. Where applicable, they will also identify different variables

which may affect the investigation and decide which variables will be kept constant and which

one is going to be altered. They will also indicate which measurements are to be taken,

decide upon the number of readings, repetition of readings and the range of readings. Safety

precautions also need to be pointed out. Any sources which are consulted during research

must be clearly identified. Before students carry out the investigation the teacher goes

through their plan and indicates any incongruent steps in their plan, lack of precision and

safety hazards.


Support for weaker students: Investigations chosen need to involve a very simple task.

Introductory lessons will include discussions and may also include preliminary experiments

to help them understand the purpose of the investigation, as well as to revise scientific ideas

covered in previous lessons. Structured prompt sheets will also help students to work

through the investigation.

1.3.2 Carrying Out the Investigation and Collecting Evidence

Following the teacher’s indications students review their plan and modify or extend it as

necessary. They then proceed to carry out the practical steps according to their plan.

However, they may vary their approach and alter parts of their investigation, as they proceed.

Any changes from the original plan will be recorded and explained in the evaluation section.

Whilst carrying out their experiment students are expected to use scientific apparatus safely

and skilfully, paying attention to the precision of measurements and observations within an

appropriate scale of operation. Collecting and recording data can include observations and

(or) table of results. Data presented at this stage should show a degree of understanding of

how to ensure results are of good quality. Therefore, all results need to be presented, even

the ones which indicate errors. Measurements taken need to include a good number of

readings, a suitable range and any repeated readings. A labelled diagram of the apparatus

used is drawn in this section.

1.3.3 Analysis of Evidence and Drawing A Conclusion

At this stage, the data obtained is processed to identify any patterns in the evidence collected.

Necessary calculations are worked out and graphs are plotted where applicable. Students

draw conclusion(s) based on observations, patterns, trends etc. The conclusions should be

related to scientific knowledge and understanding.

1.3.4 Evaluation of the Investigation

During the evaluation, students are encouraged to reflect upon their work and evaluate the

quality of the investigation undertaken. Any modifications carried out to the original plan as

the investigation proceeded are recorded and justified. Results are assessed for accuracy and

reliability. Anomalous results are identified and explained. Any further weaknesses in the

design are identified and improvements to the practical steps and/or collection of data are

also suggested.


1.4 Guidelines for Students - Investigations in Chemistry

When you are given a problem to investigate, you should first think about and discuss how you are

going to tackle the investigation. The following points will help you to formulate a strategy and

later on you will write a plan.

Discuss which strategy you are going to adopt

1. What are you investigating (trying to find out)?

2. Think of a practical way to investigate your idea. Use scientific

ideas that you already know to suggest practical steps to follow

in the investigation, including the apparatus you think you will

need.

3. You may consult texts and other sources to help you draw up a

plan.

4. Think about and discuss any safety precautions that you will

need to take.

Variable/s involved in the investigation

In certain investigations the results are affected

by changing factors such as temperature, time,

mass etc. These factors are known as variables.

Some variables must be kept the same. Other

variable(s) need to be changed to obtain valid

results. If you decide that your investigation

involves such variables think about and discuss:

which variables could possibly be involved in

the investigation?

which variable(s) are you going to keep

constant to make the investigation a fair test?

how you can make sure that this factor stays

the same?

which variable are you going to change?

which variable are you going to observe and/

or measure?

Readings to be taken in the investigation

how many measurements are you going to

take? [Five is the minimum number of

readings if you plan to plot a graph].

do you have a suitable range of readings?

do you need to repeat the experiment to

obtain an average reading? [This improves

reliability].

in what format are you going to present

your measurements?

Once you have an idea about the strategy that you are going to adopt, proceed to write a plan.

The plan needs to include the practical steps that you are going to follow, what you intend to

observe / measure and safety precautions. The plan must be checked by your teacher before you

go ahead with the investigation.

Think about

and discuss


After carrying out the investigation look closely at your results and decide whether

or not you have solved the problem, then write an evaluation of your work.

Your write up of the investigation should be divided in the following 4 sections;

a plan of the investigation;

a record of observations /measurements;

conclusion/s based on evidence obtained; and

an evaluation of the investigation.

P: Planning the Investigation

Write out a plan for your investigation. Your plan should include:

the purpose of the investigation. a list of the apparatus to be used. [Select the most suitable equipment to get accurate

results as in the given example.]

the practical steps that you intend to follow. the variables that you are going to keep constant and the one that is going to be changed [if

applicable to your investigation].

the measurements to be taken [if applicable]. any safety precautions that need to be taken, including

handling of equipment and chemicals. [Find out if any

chemicals that you plan to use or any products that might

be formed are dangerous in any way]. State also any

necessary precautions needed to improve experiment.

references of the sources consulted.

Make sure your teacher checks the plan before you carry out the investigation

E.g. of Factors (Variables)

volume & concentration

of an acid

temperature

time

amount of reacting

substances.


O: Observing / Measuring and Recording

Whilst carrying out the experiment:

Make and record observations accurately.

Record readings [if applicable].

Tables are a good way of recording measurements.

Check whether you have:

a good number of readings

a suitable range of readings

any repeated readings

Draw a labelled diagram of the apparatus used.

If at this stage you decided to make changes to your

original plan (e.g. change the order of the procedure

or include further practical steps; make use of other

suitable apparatus; make changes to the type of

measurements to be taken etc.) these should be noted

and included in the evaluation section.

A: Analysing Evidence to Draw a Conclusion

Work out any necessary calculations.

If relevant to your investigation plot a line graph or

a bar chart.

Look at your results and discuss what you have found.

Is there a pattern in your results? If so, can you

explain the pattern?

What conclusion can you draw from the results?

If you have plotted a graph (or bar chart), what can

you say about the pattern between the variables?

When you have come to one or more conclusions,

try to support them using your knowledge of

Chemistry.

If you have several readings you

will need a table like this:

Time

(seconds)

Volume

of gas

(cm3)

0

30

60

Units are to be written with the

variable in the heading of the

table as above. All variables are

to be quoted to the same

number of d.p.

Student’

s

sheet

volu

me of g

as in

cm

3

time in seconds

Remember to :

choose a suitable

scale

label your graph

axes and units

write a title of the

graph


E: Evaluating the Investigation

Look back at your investigation and think about

what went well and what could be improved.

Some of the points you might include are:

Whilst carrying out the investigation,

did you make any changes or additions to

your original plan?

If so, state what these were and give

reasons why they were necessary.

Comment on the quality of the investigation.

How accurate were the results? [make a note of

any unusual observations/ results and suggest

what could have caused those errors].

Should some tests/ steps have been repeated to

get more reliable results?

Were the results good enough to draw a suitable

conclusion?

Was this the best way of doing the investigation?

Comment on any improvements you could make to:

the practical steps.

obtain better results/ readings.

make the results more reliable.

include other factors which could be

taken into account.

obtain additional information that

improves the quality of your investigation.

Evaluation of

investigation

The results were good

but we only carried out

the experiment at two

different temperatures.

If the experiment was

repeated at another

temperature it might

have given a better

result.

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1.5 Prompt Sheets

Students will need scaffolding to provide them with a framework, which supports them in

making decisions about planning and conducting investigations. A Prompt Sheet such as the

one below will be useful to help students through a sequence of decision-making steps as they

plan and conduct their investigation, analyse their data and evaluate their investigation. The

support provided by the sheets will reduce the students’ dependence on their teachers for

instructions and thereby reducing the teacher’s management problems.

SECTION 1: PLAN

What are you going to investigate?

(focus on the problem and formulate a question for

investigation)

What do you think will happen?

(make a prediction)

Why do you think it will happen?

(justify prediction using existing knowledge, beliefs

and experiences)

What equipment will I need?

What am I going to do?

Which variables are you going to:

Change?

Measure?

Keep the same?

How will I make it a fair test?

(refine their plan to ensure that the tests are fair and

variables are controlled)

Are there any precautions that you need to take

into consideration to obtain accurate and reliable

results?


SECTION 2 : CONDUCTNG THE EXPREIMENT AND WRITING OBSERVATIONS

Carry out some preliminary trials.

Were there any problems?

How did you modify the experiment to fix

the problems?

Collect and record data in a table

or

Describe observations and record your results

Draw a labelled diagram of the experimental set-

up

SECTION 3 : DATA ANALYSIS AND DRAWING CONCLUSIONS

Can your results be presented in a graph?

Analyse your data

are there any patterns or trends in your

data?

what is the relationship between the

variables investigated?

Using science concepts explain the patterns,

trends or relationships you have identified in your

data. What is your conclusion?

What did you find out about the problem you

investigated? Was the outcome different from

your predictions? Explain.

SECTION 4 : EVALUATION

What difficulties did you experience in doing this

investigation?

How could the design of the experiment be improved to reduce error?

(Adapted from prompt sheets provided by Hackling, 2005)


1.6 Examples of Investigations in Chemistry1

Form 3

a. Hidden Blue Gems Separation techniques

b. Are red petals really red? Separation techniques

c. What makes a good indicator? Acids, Bases and Salts

d. Preparation of salts Acids, Bases and Salts

Hidden Blue Gems!

In a road block, a policeman suspects that a man has been smuggling blue gems

inside bags of copper (II) sulfate crystals, which are usually sold for agricultural

purposes. The policeman seized the smuggled goods and has sent

a sample to your laboratory for further investigation.

Plan an investigation to show whether the sample contains blue gems or not, and at the same

time return the copper (II) sulfate crystals to the owner.

Are Red Petals Really Red?

Joseph and Mary were having an argument about the pigments in red petals. Joseph

said that red petals can only contain a red colour. Mary, on the other hand, said that

the red colour could actually be a mixture of colours. They knew that you have learnt

about investigating pigments in your Chemistry lessons, so they ask you to check who

is right.

Plan an experiment to investigate if the pigment in red petals consists of one or more colours. In

your investigation think about how you can extract the pigment and check whether it consists of

one or more colours.

1 Examples taken from Investigations in Chemistry (Evans & Mizzi, 2007).

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What Makes a Good Indicator?

The juices of plants will sometimes change colour if you mix them with an acid or an

alkali. You are going to investigate the use of plant materials as indicators. The

following steps will help you in designing your investigation:

Find several plant materials e.g. petals, fruits, leaves, vegetables, etc.

Discuss how to extract the juice from the plant material.

Plan the procedure to find out which plant material acts as the best

indicator with common dilute acids and alkalis.

Think about conditions needed to make a fair comparison.

How can you extend your investigation to check if the indicators can

distinguish between acids and/ or alkalis of different strengths?

Preparation of Salts

There are a number of salts used for different purposes in our life, such as eriochalcite (copper (II)

chloride) and epsom salts (hydrated magnesium sulfate). Think of a method to prepare one of the

above salts in the lab and how you can isolate the salt in a pure dry form.

In your evaluation find out how the selected salt is used in everyday life and discuss other possible

alternative routes that could be use to prepare the salt selected.

The following investigation can be used with students of weaker ability.

Preparation of Salts

There are a number of salts used for different purposes in our life, such as eriochalcite (copper (II)

chloride) and epsom salts (hydrated magnesium sulfate).

Think of a method to prepare one of the above salts in the lab. Consider:

which reagents you are going to use.

how to ensure that at least one of the reagents is completely reacted.

how to remove impurities or unreacted reagents.

how to isolate the salt in a pure dry form.

safety procedures.

In your evaluation find out how the selected salt is used in everyday life and discuss other possible

alternative routes that could be use to prepare the salt selected.


Chemistry Form 4

e. Indigestion tablets Volumetric analysis

f. Corrosion of metal objects Metal reactivity

g. Investigating Electrical Cells Electrochemistry

h. Can you help the warehouse manager? Qualitative analysis

i. Does rainwater corrode all types of rock? Reaction of an acid on a carbonate

Does rain water corrode all types of rock?

Rain water is a very weak acid. Probably you have never seen rainwater reacting

with rock because if a reaction does take place, it would be very slow. On the other

hand you have probably seen the effect of weathering on some buildings,

so some sort of reaction does occur.

In this investigation, you will use a very dilute acid instead of rain water and you will

be provided with different samples of rocks. Some of the rocks will be in a lump form while others

will be powdered, but they have roughly the same mass.

Plan an investigation to check if the samples of rocks are worn away or not. Also determine if

there is a pattern in the reactions.

The wearing away of rocks by rainwater is an example of chemical weathering. In your evaluation

write a short paragraph to describe the weathering of limestone by rainwater and its effect on our

everyday lives.

Materials which can be used in this investigation include:

dilute hydrochloric acid

rock salt (sodium chloride)

malachite (copper (II) carbonate)

chalk (calcium carbonate powder)

marble chippings

sand

dolomite (magnesium carbonate) Materials which can be used to test for gases:

splints

lime water

litmus paper


Indigestion Tablets

Martin is suffering from an upset stomach. After paying a visit to the doctor he found that his

stomach is producing excess acid. The doctor prescribed a medicine which contains an antacid to

remove the pain in his stomach.

Indigestion medicines are found to contain a base to neutralise the excess acid. Your

teacher will provide you with two common indigestion medicines in powdered form such

magnesium hydroxide and sodium hydrogen carbonate. Hydrochloric acid will also be

provided which is the acid found in your stomach.

Design and carry out an investigation to find which of these two indigestion medicines works best.

Corrosion of Metal Objects

Acid rain has become a major concern because of its devastating effect on the

environment. One of the effects of acid rain is the corrosion of metal structures,

such as bridges, metal plated domes, monuments and window frames. Some

points that can be investigated about this problem are:

Which metals are corroded by an acid and which are not?

Do some metals corrode faster than others?

Are some acids less corrosive than others?

Whilst planning your investigation think about how you are going to make a fair comparison

between the metals.

Evaluate your investigation in the usual way and also include your comments about how fair the

comparison between the metals was.

The corrosion of a metal by an acid is a redox reaction. Select the metal which has corroded most

and use ionic equations to explain why its reaction with one of the acids is a redox reaction.

Materials which can be used in this investigation include:

dilute sulfuric acid , hydrochloric acid, ethanoic acid, magnesium, aluminium, zinc, iron (nail), copper.


Investigating Electrical Cells

Alessandro Volta is known for the development of the

electric cell in 1800. The cell made by Volta consists of two

electrodes; one made from zinc and the other of copper.

The electrolyte is sulfuric acid as shown in the diagram.

The metals have different reactivities.

The more reactive metal becomes the negative pole from

which the electrons flow in the external circuit

Plan an experiment in which you are to design an electrical

cell with the highest output.

In your investigation think about:

which factors may affect the output of the cell.

which factors you will investigate and which you are going to keep constant.

how you will measure the output of the cell.

how you can make sure that you use a ‘pure’ metal surface.

how you can make sure that the experiments planned are safe to carry out.

Can You Help the Warehouse Manager?

Some bags of different salts have arrived at a warehouse. The new store man has put the bags of

white powders in the storeroom without labelling them!

The list of salts in the bags is:

Bath salts (sodium carbonate)

Common salt (sodium chloride)

Epsom salts (magnesium sulfate)

Smelling salts (ammonium carbonate)

The warehouse manager asks you to help in identifying the powders. Plan a series of tests that

you could carry out on samples of the white solids in order to identify the cation and anion in each

salt.

zinc copper

sulfuric acid


Chemistry Form 5

j. Potato power Rates of reaction

k. Recycling zinc Rates of reaction

l. Corrosion of Marble Rates of reaction

m. How cloudy can it get? Rates of reaction

n. Which is the best fuel to boil water? Energetics

o. Investigating the amount of calcium carbonate in egg shells Rates of reaction

p. Investigating the amount of slats in energy drinks

Potato Power

Hydrogen peroxide solution decomposes very slowly at room temperature to

liberate a gas. Potato contains an enzyme which is thought to affect the

decomposition of hydrogen peroxide. Other materials like celery and liver are

also thought to influence the decomposition of hydrogen peroxide. A

company asks you to extract the enzymes present in these substances and

check if they really break down the hydrogen peroxide.

Plan an investigation in which you will extract the enzymes present in each

substance and determine how each extract affects the rate of decomposition

of hydrogen peroxide.

Recycling Zinc

A recycling company wants to set up a process to remove a thin coating of zinc

found on discarded objects that were once galvanised. The company decides to

use a dilute acid for the process. Unfortunately, the reaction using dilute acid is

slow and so the company decides to look for ways of speeding up the reaction.

Imagine that you have been asked to look for ways of speeding up the process.

Plan an experiment to find the conditions that would enable the zinc to be

removed at a faster rate.

Corrosion of Marble

Marble and dilute hydrochloric acid react to liberate a gas. It is claimed that

the rate of evolution of gas is affected by various factors. Plan an

experiment to investigate the effect of one factor on the rate of reaction.


How Cloudy Can it Get?

Sodium thiosulfate and dilute hydrochloric acid are colourless solutions but when they are reacted

a solid is produced which makes the reaction mixture turn cloudy.

Plan an experiment to investigate what can be done to the reaction to make it turn cloudy in a

shorter time.

Which is the Best Fuel for Boiling Water?

Mark and Louise are planning to go camping next weekend. Among the things they

need is a spirit cooking stove to boil water. However they have not decided which

liquid fuel to use in the stove.

Design an investigation to help them select the best fuel they should use to boil

water. In your plan describe how you are going to determine which is the best fuel

of the given selection.

Materials which can be given are methanol and ethanol.

Investigating the amount of calcium carbonate in eggshells2

Calcium carbonate occurs naturally as limestone, marble and chalk. It is also found in

eggshells and seashells, to which it provides hardness and strength. By applying your

knowledge of the general patterns of reactions of carbonates, design an investigation

to estimate the amount of calcium carbonate present in an eggshell.

Investigating the amount of salts in energy drinks

After strenuous exercise our body loses water and salts. Salts are necessary for transmitting nerve

impulses and proper muscle function. A slight depletion of the salt concentration can cause

problems. Energy drinks are generally consumed after training to replace the salt loss.

Design an investigation to estimate how much salts are provided by different energy drinks found

on the market.

2 The last two investigations were designed by Chemistry teachers and are found in the SEC syllabus 2013


1.7 Students’ Difficulties When Conducting Investigations

Some of the possible factors that may influence the performance of children doing an

investigation are:

I. the level of difficulty of the concepts within subject area.

II. the context within which the investigation is set. (students perform better when

context is scientific than when the problem was situated in an everyday context)

III. the procedural complexity of the investigation in terms of its variable structure.

IV. the openness of the question.

V. the age of the pupils – pupils performance improves with age especially the ability

to interpret evidence and draw generalisations.

VI. pupil factors – motivation, expectations, perceptions, gender, culture.

VII. teacher’s perceptions. Students encounter the following difficulties whilst conducting investigations:

Writing out the plan

Many times students write out plans for their investigation that lack detail and miss out many

steps, which are required at the planning stage. A prompt sheet helps the students to write

their work in a structured and ordered manner. It is commendable that an investigative

approach is also used in the usual type of practical work. For instance, students can be given

the necessary apparatus but then in groups they have to plan the procedural steps for their

experiment. Students’ ideas are shared, discussed and any queries are cleared out before

starting the experiment.

Variables

Terms such as ‘independent’ and ‘dependent’ variables need to be explained to students. The

independent variable is that factor that is changed through the experiment and the dependent

variable is the data that will be collected from the experiment. Having more than one variable

in the experiment will also increase difficulties. At secondary level, many students would not

have reached the formal operational thinking; therefore they find it difficult to understand

that only one variable is changed and all others are held constant (Frost 2010). Most students

are able to design a successful investigation when it involves one independent and one

dependent variable (Gott and Dugan, 1995). Prompt questions in the planning sheet will help

students to decide which variable is to be changed and which variables are to be held


constant. The concept of fair testing should be introduced with students at lower secondary

level in simple investigations. Therefore, students would start gaining experience about

controlled and manipulated variables.

Conduction of the investigation and collecting evidence

Students will be eager to start conducting their experiments however they might have missing

apparatus or the planned procedure might not be so systematic in collecting data. They might

be unsure as to what measuring instruments they need to use. When it comes to making

measurements they are not certain about the range and interval of measurements, when and

how often to measure and when to take repeated measurements (Gott & Duggan , 1995).

Before students start their work ensure that students can explain clearly what they are about

to do. If students are finding difficulties, use prompt questions to help them think and find

their own solutions; do not tell them your own solution to the problem. Students can come up

with different ideas from what the teacher has thought of and these ideas can still work out.

When gathering continuous data carrying out trail runs will help students decide on the range

and the number of data to be collected.

Data handling - Students generally encounter difficulties in how to present their evidence.

Tables are a good and efficient way of presenting data. Some guidance may be needed to

present data in a table format. As students gather evidence go around to check the data being

collected and ask questions to help students decide whether sufficient data has been collected.

Anomalous results are not discarded at this stage but then they will be processed in the

section of analysing evidence.

Analysing evidence collected and drawing conclusions

Students are at times perplexed as to how to interpret the data collected. In their report

they rewrite their results without any interpretations. As the complexity of data increases, so

the interpretation of the data becomes increasingly difficult. Guidance and prompt questions

need to be put forward to help students seek patterns in their data e.g. in the investigation

about ‘finding the best indicator’ the following questions help students process their data:

For each indicator tested:

Does it distinguish between an acid an alkali?

Does the indicator distinguish between the different strengths of acids and alkaline

solutions used?

Rank the indicators tested. Which is the best indicator? Why is it the best?


The following prompt questions will help students process numerical data:

“Which is the highest and which is the lowest number?

'Are the numbers increasing, decreasing, staying the same, or do they seem to change

randomly?

Is there any number which is vastly different from the others?

(Frost, 2010, p. 199).

When graphs are plotted guidance needs to be given how to plot a graph and how to

interpret graph. When drawing conclusions students may also find it challenging to give

generalised statements from the patterns in the data collected.

Evaluation of the investigation

Many a times students would not have evaluated the results of the usual experiment. In this

section they have to explain what procedures were changed whilst doing their investigations

and why were they changed from their original plan. They also have to process the accuracy

the reliability of the data collected. They will also need to discuss the validity of the data, if

variables were not well controlled the data will not be valid even though the aim was to carry

out a fair test. Prompt questions are also necessary to process the investigations.


1.8 Exemplars of Investigative Work and Marking Scheme

What Makes a Good Indicator?

The juices of plants will sometimes change colour if you mix them with an

acid or an alkali. You are going to investigate the use of plant materials as

indicators.

The following steps will help you design your investigation:

Find several plant materials e.g. petals, fruits, leaves, vegetables, etc.

Discuss how to extract the juice from the plant material.

Plan the procedure to find out which plant material acts as the best

indicator with common dilute acids and alkalis.

Think about conditions needed to make a fair comparison.

How can you extend your investigation to check if the indicators can distinguish between acids and/ or alkalis of different strengths?

The report of a problem solving investigation is divided into 4 parts:

a plan of the investigation;

a record of observations /measurements;

conclusion/s based on evidence obtained; and

an evaluation of the investigation.

P: Planning the Investigation

Write out a plan for your investigation. Your plan should include:

purpose of the investigation Why are you carrying out the investigation?

practical steps The practical steps that you intend to follow (preferably, also

including reasons for the choice/order of the proposed steps).

list of apparatus Select the most suitable equipment to get accurate results

fair tests Which conditions are required for fair testing?

observations to be taken Draw a table of results to be noted.

precautions Write precautions that need to be taken in order to attain more

accurate results.

references Quote the name of the books or internet sites that you used

during the research stage.

Make sure your teacher checks the plan before you carry out the investigation


PLANNING SHEET PER GROUP

Purpose of the investigation

Practical steps

List of apparatus required

Fair tests

Observation to be taken

Precautions

References


O: Observing / Measuring and Recording

Whilst carrying out the experiment:

Make and record observations accurately.

Record readings in a table of results.

Include the photos taken during the session to show evidence of investigation.

Draw a labelled diagram of the apparatus set up used during the investigation.

If at this stage you decided to make changes to your original plan (e.g. change the order of

the procedure or include further practical steps; make use of other suitable apparatus; make

changes to the type of measurements to be taken etc.) these should be noted and included in

the evaluation section.

A: Analysing Evidence to Draw a Conclusion

Look at your results and discuss what you have found.

Is there a pattern in your results? If so, can you explain the pattern? E.g., are different or similar colour changes in acidic or alkaline solutions when different indicators are used?

What conclusion can you draw from the results?

For each indicator tested

Does it distinguish between an acid an alkali?

Does the indicator distinguish between the different strengths of acids and alkaline solutions used?

Rank the indicators tested. Which is the best indicator? Why is it the best?

When you have come to one or more conclusions, try to support them using your knowledge of Chemistry. - Carry out research to find out the main component present in the best indicator and how it is affected by different pH.

E: Evaluating the Investigation Look back at your investigation and think about what went well and what can be improved.

Changes in the plan Did you make any changes or additions to your original plan? If so, state what these were

and give reasons why they were necessary.

Quality of the investigation. How accurate were the results? [make a note of any unusual observations/ results and

suggest what could have caused those errors]. Should some tests/ steps have been repeated to get more reliable results? Were results good enough or do you have a good range of indicators to draw a suitable

conclusion?

Any improvements to the investigation Are there any improvements/ alternative steps you can add to your investigation?


Marking Scheme of Problem Solving Investigation What Makes a Good Indicator?

Name: __________________________________ Class: ______________

Planning and Organisation Marks

obtained Maximum

marks

outlines a simple / detailed procedure 2

plans a simple fair test 1

selects few/ all the appropriate equipment and/or chemicals 2

draws up a table of results 1

includes experimental precautions 1

utilises/ includes information from secondary sources 1

8

Carrying out the Experiment and Obtaining Evidence Marks

obtained Maximum

marks

handles chemicals and equipment correctly/ skilfully and with due regard to safety

4

records observations systematically and accurately in a table

format

4

includes appropriate labelled diagram(s) 2

10

Analysing Evidence and Drawing a Conclusion Marks

Obtained Maximum

marks

processes observations satisfactorily; identifies a general pattern in observations;

4

draws conclusions consistent with the evidence; shows application of scientific knowledge and understanding in

giving a detailed explanation that supports the conclusion

4

8

Evaluating the Investigation Mark

obtained Maximum

marks

comments on whether the procedure was devised appropriately, discusses any deficiencies in the method and describes any modifications to the investigation

2

comments on the quality of the investigation and suggests improvements

2

4

TOTAL MARKS 30


1.9 Exemplar of Students’ Work

Students’ report no. 1

Date when conducting the investigation

Section 1: Planning the investigation.

Purpose of the

investigation To find the best natural indicator

Practical steps

1. Research was done on the plants that are going to be used.

2. The solution was extracted from the plants.

The purple cabbage and beetroot were boiled in water.

The black berries and cherries are blended.

3. Five drops of each solution was added to 5cm3 of strong acid.

4. Five drops of each solution was added to 5cm3 of weak acid.

5. Five drops of each solution was added to 5cm3 of strong acid

6. Five drops of each solution was added to 5cm3 of strong alkali.

7. Five drops of each solution was added to 5cm3 of weak alkali.

8. Record results.

List of

apparatus and

materials

Hydrochloric acid, sodium hydroxide, measuring cylinder, citric acid, ammonium

hydroxide, 8 test tubes, distilled water, pipette, beetroot solution, purple cabbage

solution, cherry solution, black berry solution.

Fair testing The same amount of plant solution. (that is same volume of solutions)

The same amount of acid and alkali was used.

How will you remove the pulp of the fruit from the juice?


Observations

Write down the colour changes noted

Beetroot Cabbage Berries Cherries

HCl

NaOH

C6H8O7

NH4OH

Safety

Precautions

1. Care was taken when handling the acid and alkali.

2. Care was taken when using the blender and handling boiling water.

References

http://chemistry.about.com/cs/acidsandbases/a/aa060703a.htm

Section 2: Observing/Measuring and Recording

Observations: The change in colour was instantaneous.

Table of results:

Cherries Black Berries Radish Red Cabbage (error due to

freshness of plant)

HCl bright pink to pale

pink black to red

pink to

orange/red brown to red

C6H8O7 bright pink to pink black to dark

red pink to pink brown to light pink

NaOH bright pink to orange black to black pink to light

green brown to light green

NH4OH bright pink to light

pink black to black

pink to

transparent brown to green

Variations from the plan:

Radish was used instead of beetroot as the beetroot wasn’t in season.

The blended mixture of both the cherries and the black berries were mixed with distilled

water then separated from the thick mixture with the use of a sieve.

Find more suitable precautions, which are needed to improve experiment or to obtain more accurate results.

http://chemistry.about.com/cs/acidsandbases/a/aa060703a.htm


Diagram:

Section 3: Analyzing Evidence to Draw a Conclusion.

Radish:

The solution extracted from the radish was able

to identify the difference between an acid and

alkali. It was able to distinguish

between a strong and weak alkali.

Red Cabbage:

This indicator did not produce the expected

results. No colour difference was obtained when

the red cabbage indicator was added to the

strong and weak acid and similarly to the weak

and strong alkali. The fact that the cabbage

wasn’t fresh was an error which means that the

results are incorrect.

strong acid weak acid weak alkali strong alkali

HCl C6H8O7 NH4OH NaOH

and indicator


This picture is the result of another group of

students where the red cabbage easily identifies

both acids from alkalis and their strengths very

clearly.

Black Berries:

Black Berries were efficient at telling the

difference between an acid and an alkali. But

was poor at telling the difference of strengths of

acid and couldn’t tell the strengths of alkali.

Cherries:

The cherries had the widest range of colours. It

was able to recognize the difference between

acid and alkali’s and also their strengths.

Range from best indicator to worst:

1) Very Good indicator- Cherries as it could tell the difference between all the possibilities.

2) Good indicator - Radish as it could tell the difference of the strengths of alkali clearly, but

not of the acid.

3) Poor indicator - Black berries as they could tell the difference between the strengths of acid

slightly.

There was an error with the red cabbage so it couldn’t be added to the range.

Conclusion:

When the indicators were added the pigment in the acids was always on the reddish side while the

alkali were on the greenish side. On further research it was found that the chemical in the fruit that


changed colour depending on the pH is antocyanins. The efficiency of a plant based indicator

depends on the amount of antocyanins found in the plant. The more antocyanins the more effective

it is as an indicator.

Section 4: Evaluating the Investigation

Changes or additions to the plan:

Radish was used instead of beetroot as the beetroot wasn’t in season.

The blended mixture of both the cherries and the black berries were mixed with distilled

water then purified with the use of a sieve.

Quality of the investigation:

There was an error with the cabbage as it wasn’t fresh. This lead to inaccurate results.

A neutral solution could have been added to increase the range of observations and results.

But overall the results were good enough to draw more than a suitable conclusion.

Improvement of results:

To improve results ingredients could have been fresher.

A colour chart could have been used to identify colours more easily.

A neutral solution could have been added.

The experiment could have been repeated twice or more to validate that no errors are

present.

The pH of the indicator solution could have been taken into consideration.


Investigation: Corrosion of Metal Objects

Acid rain has become a major concern because of its devastating effect on the environment.

One of the effects of acid rain is the corrosion of metal structures, such as bridges, metal plated

domes, monuments and window frames. Some points that can be investigated about this

problem are:

Which metals are corroded by an acid and which are not?

Do some metals corrode faster than others?

Are some acids less corrosive than others?

Whilst planning your investigation think about:

Which metals will you be using?

Which acid/s will you be using?

How you are going to make a fair comparison between the metals?

Students’ report no. 2

Section 1: Planning the Investigation

We are carrying out this investigation to find out which metals corrode by an acid and the speed at

which they corrode. We will be using sulfuric acid because acid rain has sulfuric acid in it so we

will obtain the same results but in a faster time.

Method (practical steps)

Label the beakers with the names of the metals.

Fill five beakers with 50ml of sulfuric acid each.

Put the metals in the beaker corresponding to the label.

Wait and observe changes in mass at ten-minute intervals.

List of apparatus

5 beakers

Sulfuric acid

magnesium, zinc, aluminium, lead and iron

Balance

Stop watch

Variables

The acid is the same in all 5 beakers while the variables are going to be the metals.

Fair testing points:

The volume of acid and the acid type will be the same in each beaker.

The amount of each metal will be the same.

The time the metals are left in the acid will be the same for each metal.


Observations

Any observations of what happens is added to acid are noted. Then after specific lapses of times,

any changes in pH, size, weight and surface composition are recorded for the different metals and

entered in a table. At the end of the experiment, the appearance of the metal can also be compared

to a similar piece of metal that was not put in the acid to see if there were any visible signs of

corrosion.

metal aluminium iron zinc lead magnesium

mass (g)

mass after 10 minutes (g)

mass after 20 minutes (g)

Safety precautions

Handle the acid carefully to avoid any accidents.

If the acid comes in contact with the skin rinse well with water.

Metals were dried before weighing to obtain accurate readings.

The metals were taken out of the acid using tweezers as the acid is corrosive.

References

Worldacidrainsecrets.blogspot.com

www.sackschools.ca

www.rsc.org

Section 2: Recording Results and observations

Metal Aluminium Iron Zinc Lead Magnesium Copper

mass (g) 0.24 1.83 1.65 8.99 0.06 0.48

mass after 10

minutes (g) 0.24 1.83 1.64 8.99 0.00 0.48

mass after 20

mins (g) 0.24 1.82 1.64 8.97 0.00 0.47

mass after 30

mins (g) 0.24 1.82 1.63 8.97 0.00 0.47

rate of

effervescence

no

effervescence

slow (covered

in small

bubbles)

medium occasional

bubbles very fast no effervesce

total loss in

mass (g) 0.00 0.01 0.02 0.02 0.06 0.01

aluminium iron zinc lead magnesium copper

sulfuric acid sulfuric acid sulfuric acid

http://www.sackschools.ca/

http://www.rsc.org/


Section 3: Analysis of Evidence to Draw a Conclusion3

When the metals were added to the acid some of them produced effervescence at different speeds

e.g. magnesium, as soon as it was put into the acid it produced a lot of effervescence and after some

time it had completely reacted. The gas being formed when the metals (excepts Al, Pb and Cu)

were reacting with the acid was hydrogen. From this experiment the general equation was obtained,

this is

metal + acid salt + hydrogen

Mg + H2SO4 MgSO4 + H2

Fe + FeSO4 FeSO4 + H2

Zn + H2SO4 ZnSO4 + H2

Copper although decreased in mass did not react and in fact did not produce any effervescence. The

decrease in mass may have been due to some impurities on copper reacting with the acid.

Conclusion:

From the results it was noted that not all the metals react with an acid. The metals of group two

react with an acid faster than the transition metals in fact some transition metals like gold and silver

do not even react. This is also proven by this experiment as magnesium which is in group two

reacted very fast, while zinc and iron which are transition metals reacted at much slower rate while

copper which is also a transition metal did not even react. The reactivity of the metals can also be

seen by comparing the rate of effervescence of each metal.

Metal Rate of effervescence

magnesium very fast

zinc medium

lead slow (occasional bubbles)

iron slower than lead (covered in small bubbles)

copper no effervescence

aluminum no effervescence

Aluminum did not react because it has oxide layer which protects and prevents it from reacting to

an acid for this to be avoided the aluminum could have polished to remove the oxide layer.

3 In table of results students put the metals in order of reactivity and lead appeared to be more reactive than iron


Sulfur dioxide found in the air as a result of fossil fuel burning and from volcanoes. The sulfur

dioxide reacts with oxygen in the atmosphere and with water vapour to form sulfuric acid. When

this acidic water vapour condenses, acid rain is formed.

Different metals have different uses. Aluminium and titanium are used in building aircrafts.

Aluminium is also used in apertures. Bronze is used for statues. Iron alloys such as mild steel are

used for buildings and general engineering purposes. Copper is an excellent conductor or heat and

is used to electrical wiring. Zinc is used for coating iron to prevent it from rusting this making it

weather proof.

From our investigation, it could be seen that magnesium and zinc were most affected with acid rain

whilst copper and aluminum are not affected. Corrosion of metals from acid rain can be prevented

by coating them with a layer of paint thus isolating the metal from contact with the atmosphere.

Galvanizing is used to protect iron or steel structures from rusting. Galvanizing involves coating of

the iron or steel with a thin layer of zinc. Zinc being more reactive than iron corrodes instead of

iron, this preventing the iron or steel structure from corroding.

Section 4: Evaluating the Investigation

During the experiment there were some changes to the plan. First of all we decided to use 6 metals

instead of 5 and added copper. We also measured the mass after 30 minutes as we had excess time.

The results obtained were as expected except for copper. It was not expected that copper would

react with the acid, however the results obtained may have been due to impurities with the copper

which may have reacted with the acid. An alloy such as bronze could have been added as another

metal since many outside statues are made of bronze. This experiment could also be done using a

weak acid to see what difference in the effects of metals.

A water bath could have been used at the beginning of the experiment to speed up the reaction.

This experiment although successful could have been carried out in more ways, one of which would

be to collect the escaping hydrogen from each metal, measure the volume of it and then comparing

it to the other metals to make a reactivity table on the amount of hydrogen produced.


Index page

1.1 Guidelines for Teachers 2

1.2 Objectives and Learning Outcomes of Investigative Practicals 3

1.3 Skill Areas in Investigations

1.3.1 Planning the investigation

1.3.2 Carrying out the Investigation and Collecting Evidence

1.3.3 Analysis of Evidence and Drawing Conclusions

1.3.4 Evaluation of the Investigation

4 4 5 5 5

1.4 Guidelines for Students – Investigations in Chemistry 6

1.5 Prompt sheets 10

1.6 Examples of Investigations in Chemistry 12

1.7 Students’ Difficulties When Conducting Investigations 20

1.8 Exemplars of Investigative Work and Marking Scheme 23

1.9 Exemplars of Students’ Work 27

References Evans, J. & Mizzi, D. (2007). Investigations in Chemistry – Support Pack.

Frost, J. (2010). Learning to Teach Science in the Secondary School. London: Routledge.

Gott, R., & Duggan, S. (1995). Investigative work in the science curriculum. Buckingham: Open

University Press.

Hackling. M. W., (2005) Working Scientifically: Implementing and Assessing Open Investigation

work in Science – A resource book for teachers of primary and secondary science. Department of

Education and Training, Western Australia.

Wellington, J. & Ireson, G., (2008). Science Learning, Science Teaching. London: Routledge.

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