question 1 organic chemistry multiple choice questions · 2012. 11. 10. · question 1 organic...

St Mary’s Waverley Physical Sciences Preliminary Examination Paper II – September 2011 of 20

Question 1 Organic Chemistry Multiple Choice Questions

For each of the following questions, write down the question number and the letter indicating your choice of answer.

1.1 Identify the homologous series to which this compound belongs:

A alkenes

B ketones

C alcohols

D aldehydes (2)

1.2 The general formula for the alkynes is

A CHn

B CnH2n+2

C C2nHn-2

D CnH2n-2 (2)

1.3 Which of the following sets of information are true of thermoplastics?

Melting point Flexibility Example

A high Flexible & can stretch under tension polystyrene

B low Rigid and brittle melamine

C low Flexible & can stretch under tension nylon

D high Rigid and brittle formica (2)

1.4 What substance, when added to a diol in a reaction, allows for the formation of a polyester?

A di-carboxylic acid

B alkene

C free radical

D water (2)

1.5 Ethanol is oxidised by acidified potassium dichromate, and a colour change from orange to green is observed. Distillation is required because a mixture of products results, but the major product is:

A B C D

(2)

[10]


Question 2 Organic Chemistry Nomenclature and Reactions

2.1 Provide the IUPAC name for the following compounds:

2.1.1

(4)

2.1.2

(2)

2.1.3

(4)

2.2 Look at the following two reactions and answer the questions that follow:

Reaction A:

Reaction B:

2.2.1 Name the type of reaction that occurs in Reaction A. (1)

2.2.2 State what would be observed in Reaction B and explain the observation. (4)

Both of these reactions result in the same haloalkane being formed.

2.2.3 Which reaction would you expect to occur more quickly? (1)

2.2.4 Explain your answer to 2.2.3. (2)


2.3 Amy plans to use three different haloalkanes in an investigation: chloromethane, bromomethane and iodomethane. Unfortunately, the bottles have become mixed up and are only labelled 1, 2 and 3.

In corresponding test tubes (i.e. also labelled 1,2 and 3), she heats each of the haloalkanes with dilute sodium hydroxide to get the relevant sodium halide into solution. An incomplete generalised reaction is shown below:

2.3.1 Name ‘Product 1’ in this reaction. (1)

Now that the halides are in solution, Amy tests them each by adding silver nitrate to the test tubes. Her observations are given below:

Test tube Observation after silver nitrate is added

1 clear, colourless solution becomes opaque cream-coloured

2 clear, colourless solution becomes milky white

3 clear, colourless solution becomes opaque and light yellow

2.3.2 Name the type of reaction that occurs when the silver nitrate is added. (1)

2.3.3 The product that results in the light-yellow colour in test tube 3 is an iodide. Give the formula of the product. (2)

The following questions refer to chloromethane:

2.3.4 Give the number of the bottle that contains chloromethane. (1)

2.3.5 Give the Couper structure of chloromethane. (1)

2.3.6 Use electronegativities to determine the nature of the bond between the chlorine and the carbon in chloromethane. Show any working. (4)

2.3.7 Is chloromethane polar or non-polar? (1)


2.4 Look at the following unbalanced equation and answer the questions that follow:

C8H18 + O2 CO2 + H2O

2.4.1 Name the type of reaction that is depicted above. (1)

2.4.2 Do you expect the heat of the reaction, ΔH, to be positive or negative? Give a reason for your answer. (3)

2.4.3 Briefly explain how reactions like these negatively affect our environment. (4)

2.4.4 Rewrite the equation above, balance it and add phase labels (s, ℓ, g and/or aq). (3)

In this reaction (at STP), 60 moles of O2 is added to 456 g of C8H18.

2.4.5 Calculate the number of moles of C8H18. (5)

2.4.6 Hence, calculate which reactant is in excess and by how many moles. (4)

2.5 Methyl butanoate is a chemical substance that smells like pineapple.

2.5.1 To which homologous series does methyl butanoate belong? (1)

2.5.2 Draw the structural formula for methyl butanoate. (3)

2.5.3 Name the two substances that would be used to prepare methyl butanoate in a laboratory. (2)

2.5.4 Draw the structural formulae of two isomers of methyl butanoate. (4)

A catalyst is required in this reaction.

2.5.5 What is the catalyst that is used in this reaction? (2)

2.5.6 What is the function of a catalyst, and how does it achieve its function? (2)

[63]


Ethenol

Question 3 Plastics & Polymers

3.1 What is meant by ‘free radical’? (2)

Polymers are made by joining alkene monomers into very long chains which have C – C bonds. Initiation of a polyethylene chain is as follows:

3.2 Is this an example of addition or condensation polymerisation? (1)

3.3 Name the process that occurs directly after initiation. (1)

3.4 Using the molecules from the initiation reaction above depict the process in 3.3 using structural formulae. (4)

Other polymers produced by this type of polymerisation are polyethenol (also known as polyvinyl alcohol or PVA) and polypropylene (also known as polypropene). The structure of ethenol is shown in the box alongside.

3.5 Draw the structural formula of a ‘polymer’ of polyethenol that has three repeating units. (3)

3.6 Write the chemical formula of propene. (1)

3.7 Rank the melting points of polyethylene, polyethenol and polypropylene in order from lowest to highest and explain your answer. (8)

[20]


Question 4 Rates of reaction experiment

(Question adapted from CIE O-Level July 2009 Exam Paper 4)

An experimental investigation is carried out on the decomposition of an aqueous solution of hydrogen peroxide, (H2O2), in the presence of a catalyst.

2H2O2(aq) → 2H2O(l) + O2(g)

A pupil investigated the rate of decomposition of hydrogen peroxide by using two different catalysts, manganese (IV) oxide and copper. The pupil carried out two experiments using 30 cm3 of hydrogen peroxide solution in each experiment but with the same mass of a different catalyst in each experiment.

Experiment 1 uses manganese (IV) oxide as the catalyst.

Experiment 2 uses copper as the catalyst.

4.1 The results for experiment 1 and some of the results for experiment 2 are shown in the table below. Use the diagrams to complete the results for experiment 2 in the table. Write down the number of the question and the answer only. (2)

4.2 Provide a hypothesis for this investigation. (3)

4.3 Identify the dependent variable in the experiment. (1)

4.4 Plot the results from experiments 1 and 2 on the graph paper provided on your answer sheet and draw a smooth curve through each set of points. Label the curves 1 and 2. (8)

4.5 The experiment is carried out using a conical flask with a side arm connected to a tube which in turn is connected to the syringe. The catalyst is added to the hydrogen peroxide and the conical flask is quickly stoppered with a rubber bung. Explain the concept of accuracy and discuss why this method would not produce accurate results. (3)

4.6 Use collision theory to explain why the gradient of each graph decreases as the reaction proceeds. (2)

Time/min 1 2 3 4 5 6 Volume of oxygen collected in experiment 1/ cm3

9 17 24 29 32 35

Volume of oxygen collected in experiment 2/ cm3

4.1.1 4.1.2 4.1.3 4.1.4 50 50


4.7 Suggest which is the better catalyst, manganese (IV) oxide or copper? Explain your answer. (2)

4.8 At the end of experiment 2 the copper was removed from the solution by filtration. It was dried and weighed. How would you expect the mass of the copper to compare with the mass of copper at the start of the experiment? (1)

4.9 How would you expect this graph to change if all the conditions for experiment 2 were kept the

same except that 40 cm3 of the hydrogen peroxide solution was used? (2)

2H2O2(aq) → 2H2O(l) + O2(g)

4.10 In experiment 2 the maximum volume of O2 produced is 50 cm3.

4.10.1 Calculate the maximum number of moles of oxygen at STP. (5)

4.10.2 Use the equation for this reaction to calculate the number of moles of the hydrogen peroxide solution used. (2)

4.10.3 If the initial volume of H2O2 is 30 cm3, calculate the concentration of this peroxide solution. (5)

[36]


Question 5 The common ion effect Multiple Choice Questions

Read the information below and choose the most correct answer. Write only the question number and the letter indicating your choice of answer.

Carbon dioxide has the ability to dissolve in the water in the oceans. In aqueous solution, the following equilibrium is set up:

Reaction 1: CO2(aq) + H2O(l) H2CO3(aq) ∆ H < 0

Only about 1 % of the dissolved CO2 exists as H2CO3. Carbonic acid undergoes dissolution in two steps:

Reaction 2: H2CO3 H+ + HCO3- Ka = 4,2 x 10 -7

Reaction 3: HCO3- H+ + CO3

2- Ka = 4,8 x 10 -11

In ocean water, calcium carbonate is an important salt to have in solution because it is used by crustaceans and corals to form their exoskeletons. Calcium carbonate can set up the following equilibrium in aqueous solution:

Reaction 4: CaCO3 (s) Ca2+(aq) + CO32- (aq) Ksp = 8,7 x 10-9

5.1 At the surface of the sea the temperature of the water may increase. Use Reaction 1 to decide

whether this temperature rise would cause:

A A higher volume of CO2 to dissolve in the sea.

B The rate of the forward reaction to increase.

C The Kc value to increase.

D The surface water to be more acidic . (2)

5.2 We can see from Reaction 2 that:

A carbonic acid is highly soluble.

B carbonic acid is a dilute acid because the Ka value is low.

C at equilibrium: [products] > [reactants].

D the equilibrium lies to the left. (2)

5.3 When more CO2 dissolves into the sea over time, the H+ ion concentration reflected in Reaction 3 decreases because of the production of H+ ions in Reaction 2. Using this information, decide which one of the following might happen:

A There will be less calcium carbonate available for crustacean and coral growth because calcium carbonate comes out of solution.

B Ca2+ ion concentration in the sea will decrease because Reaction 4 shifts to the right.

C The Ka value of Reaction 3 will increase because Reaction 3 shifts to the right.

D CO32- ion concentration in the water will increase because the H+ ion concentration has

increased. (2)

[6]


Question 6 The Ostwald Process

The following three equations show the three steps in the industrial process called the Ostwald Process. The Ostwald Process is used to make nitric acid.

Step 1: 4 NH3(g) + 5 O2(g) 4 NO(g) + 6 H2O(g) ∆H < 0

Step 2: 2 NO(g) + O2(g) 2NO2(g) ∆H < 0

Step 3: NO2(g) + H2O(l) HNO3(aq) + NO(g)

The catalyst used in Step 1 is platinum at 1000oC.

6.1 Provide the name for ‘NH3’ . (1)

6.2 The reaction in Step 3 is not balanced, rewrite the equation and balance it. (2)

6.3 Other than changing the temperature, state two ways to increase the yield of nitrogen monoxide in Step 1. (2)

6.4 Refer to Step 1 and explain why the operating temperature of this industrial process has to be chosen carefully. (2)

6.5 Most chemical firms do not wait for their reaction systems to reach equilibrium. Provide a reason for this. (1)

Question 6 continues on page 10...


In a simulation of the chemical reaction in Step 2 of the Ostwald process, 1 mol each of NO(g) and O2(g) were originally introduced into a 0,5 dm3 container to produce NO2. The chemical reaction is as follows:

2 NO(g) + O2(g) 2 NO2(g)

The results of the simulation are that at equilibrium there are 0,1 mol of NO(g), 0,55 mol of O2(g) and 0,9 mol of NO2(g) in the container.

6.6 In an attempt to represent these results, Suzy has plotted the sketch graph (without values) below showing the concentration of gases in a reaction vessel over time for the chemical.

6.6.1 When Suzy drew the graph above, she made three errors. Identify these three errors. (3)

6.6.2 Comment on the rate of the forward and reverse reactions at time t1 on the graph. (1)

6.7 Using the correct results from the simulation (given in the box above):

6.7.1 Write the expression of mass action for the chemical reaction. (3)

6.7.2 Calculate the equilibrium constant. (3)

6.8 Suppose that the pressure of the system was increased at time t2 (assume temperature remains constant). Explain what would happen to the equilibrium system by referring to Le Chatelier’s principle. (4)

6.9 The graph above has been reproduced on your answer sheet. Show the effect of the disturbance in 6.8 on the system on the amounts of NO2, O2 and NO by completing the lines on the graph. You do NOT need to calculate actual values, but you will be given credit for showing the relative changes in the amounts of NO2, O2 and NO. (Note: the labels of the lines have been removed to make space for you to complete the lines, so it will therefore be necessary for you to re-label the lines.) (5)

6.10 How would the value of the equilibrium constant just after time t1 compare to the value of the equilibrium constant when equilibrium had been reached after time t2? (1)

NO2

NO

O2

t1 t2

Concen

tration

Time (secs)

A graph showing the change in concentration of reactants and products over a time period in a chemical equilibrium reaction.


Nitrogen dioxide is prepared in the school laboratory using a different chemical reaction to the one used in Step 2 of the Ostwald process. This chemical reaction is as follows:

Cu(s) + 4 HNO3(l) → Cu(NO3)2(aq) + 2 H2O(l) + 2 NO2(g)

6.11 Calculate that the molar mass of NO2(g). (1)

6.12 NO2(g) is collected by displacing air. Consider the density of NO2(g) and choose the correct answer from the options below to decide how this gas is collected. (2)

6.13 Redraw the apparatus below to show how it should be set up to make NO2 gas. (5)

6.14 What would you observe on the sides of the glass reaction vessel? (1)

6.15 State two ways (other than changing temperature) in which the rate of this reaction can be increased. (2)

[39]

Choice Density Collection method

A NO2(g) is denser than air Collected by the downward displacement of air

B NO2(g) is denser than air Collected by the upward displacement of air

C NO2(g) is less dense than air Collected by the downward displacement of air

D NO2(g) is less dense than air Collected by the upward displacement of air

Copper turnings Nitric

acid


Question 7 Redox Reactions and Batteries

In an acidic solution, Fe2+ ions are oxidised to Fe3+ ions by hydrogen peroxide (H2O2).

7.1 Give the definition of a redox reaction. (2)

7.2 Use the table of reduction potentials to give the oxidation half reaction for this reaction. (2)

7.3 Two reactions containing H2O2 appear on the table of reduction potentials. For the reaction described above, which one of the two half reactions reproduced below (A or B) is the correct reduction half reaction? A H2O2 + 2 H+ + e- 2 H2O B H2O2 O2 + 2 H+ + e- (1)

7.4 Give a reason for your choice in question 7.3 above. (1)

A set of chemicals is given to students in a laboratory in order to determine the relative reactivity of certain metals.

The metals are: Zn, Cu, Mg, Fe

The following solutions were also supplied: Zn(NO3)2, Cu(NO3)2, Mg(NO3)2, Fe(NO3)2

The metals are placed in each of the solutions in turn and then observations are made.

7.5 Use the table of reduction potentials to help you determine which of the metals, given above, will react with all of the solutions (except for the solution containing its own ion). (2)

7.6 Use the table of reduction potentials to help you determine the reactivity series for these four metals. List the metals from least to most reactive. (2)

Batteries are an example of spontaneous chemical reactions that take place inside a cell, producing a potential difference. Some batteries are designed to be used and then discarded once the reactants have been used up. Others are designed to be rechargeable – in which case, the reaction can be reversed and the battery can once again provide a useful potential difference.

One particular rechargeable battery is the lead-acid cell of a car battery.

When this cell discharges during the spontaneous reaction, the following reactions take place:

Oxidation ½ reaction: Pb(s) + SO42- → PbSO4(s) + 2e-

Reduction ½ reaction: PbO2(s) + SO42- + 4H+ + 2e- → PbSO4(s) + 2H2O

7.7 What is the reducing agent in the lead-acid cell during discharge? (1)

7.8 Determine the oxidation number of lead in the compound PbO2. (2)

When the lead-acid battery is recharged by plugging it in to a power source, the two half reactions above are reversed.

7.9 Write the overall (net) recharge reaction. (3)

7.10 The recharge reaction is not spontaneous. What indicates that this is true? (1)


Read the following extracts taken from a variety of sources. They are about lead-acid batteries, their major component, lead, and the process of recycling.

7.11 Refer to all three extracts to help you answer the following question:

Imagine that South African law makers have proposed the following legislation requiring all manufacturers of lead-acid batteries in South Africa to: • charge a deposit on all sales of batteries, redeemable when a depleted (completely used

up) battery is returned for recycling to the place where it was purchased. • accept a depleted battery for every new battery sold. • ensure that all depleted batteries are sent for recycling.

Provide a response (in point form) to the relevant law makers addressing economic, human and environmental issues. Use the following four statements to help structure your argument:

• I think that.... (1) • The evidence to support my opinion is... (6) • Argument against my opinion is.... (1) • I would counter this arguments by.... (1)

[26]

Extract 1 Most types of batteries can be recycled. However, some batteries are recycled more readily than others, such as lead-‐acid automotive batteries. The lead of the lead-‐acid battery can be recycled.

Many cities offer battery recycling services for lead-‐acid batteries. In some places (mostly in the USA), a refundable deposit is paid on batteries. This encourages recycling of old batteries instead of abandonment or disposal with household waste.

Businesses which sell new car batteries may also collect used batteries (and may be required to do so by law) for recycling. Most battery shops and recycling centres will pay for scrap batteries. This can be a lucrative business, enticing especially to risk-‐takers because of the wild fluctuations in the value of scrap lead that can occur overnight. When lead prices go up, scrap batteries can become targets for thieves.

Adapted from: http://en.wikipedia.org/wiki/Automotive_battery_recycling

Extract 2 Elemental lead is toxic and should therefore be kept out of the waste stream. However, it is a common environmental pollutant.

Lead poisoning is a medical condition caused by increased levels of lead in the body. Lead interferes with a variety of body processes and is toxic to many organs and tissues including the heart, bones, intestines, kidneys, and reproductive and nervous systems. It interferes with the development of the nervous system and is therefore particularly toxic to children, causing potentially permanent learning and behaviour disorders. Symptoms include abdominal pain, confusion, headache, anaemia, irritability, and in severe cases seizures, coma, and death.

Routes of exposure to lead include contaminated air, water, soil, food, and consumer products. Occupational exposure is a common cause of lead poisoning in adults. Battery recycling workers at lead-‐acid battery recovery facilities are at risk for lead exposure. Adapted from: http://en.wikipedia.org/wiki/Lead_poisoning

Extract 3 According to the 1992 statistics in South Africa some 65 % of all lead was used by the battery manufacturing industry as a whole. An estimated recycling rate of 68.5 % for batteries was obtained during 1992. In comparison the South African recycling rate compares very poorly with Western European countries (80 %), the USA (95 %), and Japan (97 %). These countries adopted legislation controlling the disposal of batteries and enforcing their return for processing. The fact that automotive batteries are being disposed of in informal settlements in South Africa cannot be ignored because some incidents of lead poisoning have already been reported.

Adapted from: http://devplan.kzntl.gov.za/idp_reviewed_2006_7/IDPS/KZ271/Adopted/Appendix%209_11%20Recycling%20Information.pdf


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ANSWER SHEET

EXAM NUMBER: 1 1 1 1 5 3

4.4

(8) 6.9

(5)

t1 t2

Concen

tration

Time (secs)


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question 1 organic chemistry multiple choice questions · 2012. 11. 10. · question 1 organic...

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