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HKDSE Chemistry A Modern ViewPart IX Rate of Reaction

©Aristo Educational Press Ltd. 2010 82

Structured Questions

Chemistry: Chapter 38 Rate of chemical reaction

Sections 38.138.2

1

In a chemical reaction A + B C , the amount of reactant A recorded at one-minute

intervals was shown below.

Time( t) (min) 0 1 2 3 4 5 6

Amount of A (mol) 0.800 0.400 0.200 0.100 0.0500 0.0250 0.0125

(a) Calculate the average rate of reaction (in mol s1) during the 6 minutes.

(b) Plot a graph of amount of A against time.(c) According to the graph, what is the initial rate of the reaction?

(d) According to the graph, what is the instantaneous rate at t = 3 min?

[5M]

2

In the reaction of excess magnesium and 10.0 cm3 of 2.0 M dilute hydrochloric acid,

hydrochloric acid was used up in 10 seconds and 48.0 cm3 of hydrogen was formed at

room temperature and pressure.

(a) Calculate the average rate of formation of hydrogen in cm

3

s

1

.(b) Calculate the average rate of decrease of HCl in

(i) M s1.

(ii) mol s1.

(c) Calculate the average rate of formation of magnesium chloride in mol s1.

[5M]

3

Consider the following reaction:

2NaHCO3(s) + H2SO4(aq) Na2SO4(aq) + 2H2O(l) + 2CO2(g)

When 3.5 g of sodium hydrogencarbonate was added to 25.0 cm3 of 3.0 M sulphuric

acid, the sodium hydrogencarbonate reacted and disappeared in 180 seconds.

(a) Which of the two reagents is in excess?

(b) Calculate the average rate of decrease of sodium hydrogencarbonate in g s1.

(c) Calculate the average rate of decrease of sulphuric acid in M s1.

(d) Calculate the average rate of production of carbon dioxide in g s1.

[7M]

4






Cr 2O72(aq) + 14H+(aq) + 6I

(aq) 3I2(aq) + 2Cr 3+(aq) + 7H2O(l)

25.0 cm3 of 0.25 M acidified potassium dichromate solution was mixed with 25.0 cm3

of 0.50 M potassium iodide solution. The reaction took 40 seconds to complete.

(a) Which of the two reagents is in excess?

(b) Calculate the average rate of decrease of I(aq) concentration in the reaction

mixture.

(c) Calculate the average rate of decrease of Cr 2O72(aq) concentration in the

reaction mixture.

(d) Calculate the average rate of increase of I2(aq) concentration in the mixture.

[8M]

5

In an experiment of a chemical reaction A + B C , the amounts of reactant A

recorded at one-minute intervals are shown below.

Time ( t)/min 0 1 2 3 4 5 6

Amount of A /mol 0.8 0.4 0.2 0.1 0.05 0.025 0.0125

(a) Calculate the average rate of change in the amount of A in the mixture in mol

min1 throughout the reaction.

(b) Plot a graph of ‘Amount of A’ against ‘Time’.

(c) Calculate, from your graph, the initial rate of reaction.

(d) Calculate, from your graph, the instantaneous rate at the third minute.

[8M]

6

The rate of a certain reaction is followed by measuring the concentration of a reactant





at various times in the course of the reaction. The graph as shown below is obtained.

(a) Why is the graph steepest between V and W ?

(b) Does the reaction go to completion? Explain.

(c) Suppose in this experiment, the rate of the reaction is followed by measuring the

concentration of a product at various times. Sketch the shape of the graph which

should be obtained.

[5M]

Section 38.3

7


Br 2(aq) + HCO2H(aq) 2Br (aq) + 2H+(aq) + CO2(g)

(a) Suggest and explain ONE method to monitor the change in concentration of

Br 2(aq) during the reaction.

(b) Sketch a graph to show the change of the physical parameter measured in part (a)

with time.

[6M]

8 A student finds that baking soda gives colourless bubbles when it is added to

hydrochloric acid. He wants to follow the progress of the reaction by measuring the

pressure change of the reaction system with time.

(a) Write a chemical equation to show the reaction involved.

(b) Draw a labelled diagram to show the experimental set-up.

(c) In the experiment, he used 30 cm3 of 2.0 M hydrochloric acid to react with 5 g of

baking soda. The pressure inside the container increased from 1.0 atm to 1.2 atm

in 2 minutes.

(i) Which of the two reactants is limiting? Explain your answer.

C o n c e n t r a t i o n o f a r e a

c t a n t

0 t Time

V

W

X

Y Z

excess





(ii) Calculate the average rate of the reaction in atm s1.

(Relative atomic masses: Na = 23.1, C = 12.0, O = 16.0, H = 1.0)

[8M]

9

The reaction between magnesium ribbon and dilute hydrochloric acid produces

hydrogen.

(a) Write a balanced equation for the above reaction.

(b) Draw a set-up used to follow the reaction rate of the above reaction. Also explain

why such a set-up can be used.

(c) State ONE advantage of using such a set-up to study the rate of the reaction.

(d) Sketch a graph showing the volume of gas produced against the time of reaction.

[7M]

10

It is known that NaN3 decomposes to form nitrogen and sodium. This reaction is

widely used in the inflation system of airbags of vehicles.

(a) Write a balanced equation for the above reaction.

(b) State whether the rate of reaction of the above reaction is high or not? Explain.

(c) Suggest ONE advantage of the application of the above reaction in airbags.

(d) Suggest another method to reduce the causalities of car accidents.

[5M]

11


Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)

A piece of magnesium was dropped into 0.1 M HCl and the following data was

obtained:

Time (s) Mass of magnesium (g)

0 0.30

4 0.15

8 0.10

12 0.063

16 0.043

20 0.027

(a) Calculate the average rate of magnesium consumed per second.

(b) Calculate the average rate of reaction in moles of Mg consumed per second.

(c) What would happen to the concentration of H+ as the reaction proceeds?

(d) What would happen to the concentration of Cl as the reaction proceeds?





(e) Plot a graph showing the mass of Mg against time.

(f) Suggest and explain another method which can be used to follow the progress of

the reaction.

(g) Sketch a rate curve of using the method suggested in (f).

[12M]

12

You are provided with the following materials and apparatus:

Sodium thiosulphate solution, hydrochloric acid,

beaker, glass rod, white tile, marker, stopwatch

(a) Describe how to determine the rate of the reaction, including the experimental

set-up.

(b) Write an ionic equation for the reaction between sodium thiosulphate and

hydrochloric acid.

(c) A pungent choking smell was detected during the experiment. State the origin of

this smell.

(d) (i) State the relationship between the experimental time and the rate of the

reaction.

(ii) The time for ‘blot out’ is 250 seconds. What is the rate of the reaction?

(e) (i) Suggest a measurement technique that can also be used to follow the

progress of the reaction. Explain your choice.

(ii) Explain why the above measurement technique is not better than measuring

the change in transmittance of light through the reaction mixture.

[13M]

13

Calcium carbonate is the main component of egg shells. An experiment was carried

out to determine the change of pressure of the reaction system during the reaction.

(a) What would be observed in the reaction mixture?

(b) Write an ionic equation for the reaction.

(c) What is the use of a pressure sensor?

computerdata-logger pressure

sensor

excess

dilute

HCl

egg

shells





(d) State ONE advantage of using a data-logger to do experiment.

(e) The following graph shows pressure of the reaction system against time.

(i) Comment on the shape of the graph.

(ii) Why is the pressure at time 0 not zero?

(f) Describe how to find the percentage by mass of calcium carbonate in a sample of

egg shells.

[15M]

14

Consider the alkaline hydrolysis of ethyl ethanoate:

CH3COOCH2CH3(aq) + NaOH(aq) CH3COO Na+(aq) + CH3CH2OH(aq)

The reaction progress is monitored by titrimetric analysis. At each 15-minute interval,

5.0 cm3 of the reaction mixture is transferred into a beaker and an excess fixed

amount of standard hydrochloric acid is added to it.

(a) What is the purpose of adding excess HCl to the reaction mixture?

(b) Describe how to find the amount of NaOH present in the reaction mixture.

(c) (i) State ONE alternative way instead of adding excess HCl to serve the same

purpose.

(ii) State ONE disadvantage of this alternative way.

[6M]15

A student followed the progress of the reaction between a magnesium strip and excess

dilute hydrochloric acid. The set-up for the experiment was shown below.

Time (s)

P r e s s u r e ( k P a )





During the experiment, volumes of X collected were recorded at one-minute intervals.

The results were shown below.

Time (min) 1 2 3 4 5 6 7

Volume of X

collected (cm3)

17 29 36 42 44 44 44

(a) Write a balanced chemical equation for this reaction.

(b) State what X is. Suggest a test to show its presence.

(c) Suggest TWO sources of error of using this set-up.

(d) Suggest ONE other method to follow the progress of the reaction. Explain

briefly.

(e) Do you expect that the reaction was complete by t = 6 min? Explain briefly.

(f) Plot a graph of volume of X collected against time.

(g) Sketch a graph to show the change in mass of magnesium with time.

[8M]

16

Consider the following reaction in which the reactants react completely:

2MnO4(aq) + 5C2O4

2(aq) + 16H+(aq) 2Mn2+(aq) + 10CO2(g) + 8H2O(l)

Colorimetric analysis is used to monitor the reaction progress. The reaction is carried

out inside a test tube.

(a) Describe what can be observed in the test tube when the reaction proceeds.

(b) A student argues that the colour change during the reaction is mainly due to the

formation of water which causes dilution of the solution. Comment on his

statement.

(c) Sketch a graph to show the change in concentration of MnO4 with time.

[5M]

17

The redox reaction of MnO4 and S2O3

2 is represented by the following equation:

2MnO4

(aq) + 10S2O32

(aq) + 16H+(aq) 2Mn2+(aq) + 5S4O62

(aq) + 8H2O(l)

(a) Suggest ONE method to monitor the progress of the reaction above. Explain

gas syringe

dilute hydrochloric acidmagnesium strip





your answer briefly.

(b) As shown above, the reaction takes place at acidic medium. You are given two

acids with equal concentration: ethanoic acid and hydrochloric acid. Which one

is more suitable for the reaction above? Explain your answer briefly.

(c) A student decided to use another method to monitor the progress of the reaction.

He first quenched the reaction by diluting a small portion of the reaction mixture,

then he added phenolphthalein as indicator, and titrated the quenched reaction

mixture against standard sodium hydroxide. Comment on his method.

[8M]

18

Hydrogen peroxide decomposes according to the following equation:

2H2O2(aq) 2H2O(l) + O2(g)

(a) Suggest ONE method to determine the reaction rate of the above reaction.

(b) Name the catalyst that can speed up this reaction.

(c) If a catalyst is used in the reaction, outline the procedure of a titrimetric analysis

used to follow the progress of the reaction.

(d) Balance the following ionic equation for the titration reaction.

H2O2(aq) + MnO4(aq) + H+(aq) Mn2+(aq) + H2O(l) + O2(g)

[7M]

19

Consider the following reaction in an open system:

ZnCO3(s) + 2HCl(aq) ZnCl2(aq) + H2O(l) + CO2(g)

Time (min) X

0 12.0

2 6.05

4 2.23

6 0.82

8 0.30

10 0.11

(a) State what X should be.

(b) Suggest a method to obtain the data of X .

(c) Plot a graph showing the relationship between X and time.

(d) Suggest ONE other method to measure the rate of the reaction.

[7M]

20

Suggest method(s) that can be used to measure the rate of reaction of the following

reactions. (There may be more than one method in each of the following reaction.)





(a) 2I(aq) + S2O8

2(aq) I2(aq) + 2SO42(aq)

(b) 5H2O2(aq) + 2MnO4(aq) + 6H+(aq) 2Mn2+(aq) + 8H2O(l) + 5O2(g)

(c) 2H2O2(aq) 2H2O(l) + O2(g)

[7M]

21

Consider the alkaline hydrolysis of ethyl ethanoate:

CH3COOCH2CH3(l) + NaOH(aq) CH3COONa(aq) + CH3CH2OH(aq)

The reaction progress is monitored by titrimetric analysis. At 5-minute intervals, 5

cm3 of the reaction mixture is transferred into a beaker and a fixed amount of excess

standard hydrochloric acid is added to it immediately.

(a) What is the purpose of adding excess standard HCl to the reaction mixture?

(b) State ONE alternative way instead of adding excess standard HCl to the reaction

mixture.

(c) State ONE disadvantage of this alternative way.

(d) Describe how you can determine the amount of NaOH present in 5 cm3 reaction

mixture.

[6M]

22

You are going to follow the progress of the reaction between a magnesium ribbon and

excess dilute hydrochloric acid. The set-up for the experiment is as follows.

(a) Write a chemical equation for this reaction.

(b) What is X ? Give a method to test for its presence and the corresponding

observation.

(c) Suggest ONE source of error in using this set-up.

(d) Can a pressure gauge be used instead of a gas syringe? Explain briefly.

plunger rubber connecting

tubing

dilute hydrochloric acid

magnesium ribbon

Xcotton thread

stopwatchgas syringe

MnO





(e) The volumes of X collected are recorded at one-minute intervals. The results are

shown below.

Time ( t)/min 1 2 3 4 5 6 7

Volume of X collected/cm

3

17 29 37 42 44 44 44

Do you expect the reaction to have completed by the sixth minute? Explain

briefly.

(f) Plot a graph for ‘Volume of X collected’ against ‘Time’.

(g) Sketch the graph for ‘Mass of magnesium ribbon’ against ‘Time’.

[10M]

23

Consider the following reaction.2MnO4

(aq) + 5C2O4

2(aq) + 16H+(aq) 2Mn2+(aq) + 10CO2(g) + 8H2O(l)

The reaction is carried out inside a test tube. Colorimetric analysis is adopted to

monitor the reaction progress.

(a) Describe what you can observe in the test tube when the reaction is going on.

(b) A student argues that the colour change of the solution during the reaction is

mainly due to formation of water which causes dilution of the solution. Do you

agree with him? Give your reason.

(c) Sketch the graph for ‘Concentration of MnO4(aq)’ against ‘Time’.

[6M]

Chemistry: Chapter 39 Factors affecting rate of reaction

Sections 39.139.3

24

A student did the following experiments to investigate the rate of reaction between

magnesium and different acids. Magnesium was the limiting reactant in both

experiments.

Experiment Reaction

I 1 g of Mg ribbon + 1.0 M HCl(aq)

II 1 g of Mg ribbon + 1.0 M CH3COOH(aq)

(a) Draw a labelled diagram to show the experimental set-up.

(b) Write an ionic equation for the reaction of magnesium and an acid.

(c) Suggest ONE observation to ensure that the reaction was complete.

(d) For experiment I and II, explain any difference in the





(i) initial rates.

(ii) total volume of hydrogen gas collected.

(e) Sketch, on the same graph, the rate curves which would be obtained in

experiments I and II.

(f) If 1.0 M sulphuric acid is used to react with magnesium, explain any difference

in reaction time when compared with experiments I and II.

[14M]

25

To investigate the effect of concentration on rate of reaction, you are asked to perform

an experiment. By mixing solutions of water, sodium thiosulphate and hydrochloric

acid in different proportions as follows, the time required for the solution to turn

cloudy (defined as 20% light transmittance here) are recorded.

Trial [HCl] (mol dm 3

) [S2O32

] (mol dm 3

)

Time ( t) required for

the solution to turn

cloudy (s)

1 2.00 0.250 36.0

2 1.00 0.250 48.0

3 0.500 0.250 57.0

4 0.250 0.250 68.0

5 0.125 0.250 121

6 0.0625 0.250 158

(a) Write an ionic equation for the reaction involved.

(b) Tabulate the values oft

1 for trials 1 to 6.

(c) Plot a graph oft

1 against [HCl].

(d) Describe the relationship betweent

1 and [HCl]. Do you think the relationship

between the rate of reaction and [HCl] is similar too? Explain your answer.(e) Briefly explain the effect of [HCl] on the rate of reaction.

[9M]

26

The graph below shows the volume of carbon dioxide gas produced against time

when excess calcium carbonate is added to x cm3 of 2.0 M hydrochloric acid.





(a) Write an ionic equation for the reaction.

(b) State and explain the change in the rate of reaction with time. Give a method to

determine the rate of the reaction at a particular time from the curve.

(c) Sketch, on the same graph, the curves would be obtained if:

(i) the same volume of 1.0 M HCl is used.

(ii) the volume of 1.0 M HCl used is doubled.

Label the curves and explain your answer in each case.

[10M]

Section 39.4

27

(a) A student claimed that the temperature of water is always equal to 100oC when it

boils, no matter what type of container is used. Comment on his statement.

(b) Explain, using the collision theory, why a pressure cooker can decrease the time

of cooking.

(c) Suggest ONE advantage of using a pressure cooker apart from decreasing the

time of cooking.

[6M]

28

H2O2(aq) decomposes to water and oxygen in the presence of MnO2 powder.(a) Write a balanced equation for the reaction.

(b) State the function of MnO2.

(c) Explain why MnO2 is used in powdered form.

(d) Explain whether the MnO2 powder can be reused after the reaction.

(e) Draw a set-up to follow the reaction rate of the chemical reaction.

(f) Give two critical requirements for other reactions so that the set-up mentioned in

(e) can be used to follow the reaction rate.

[10M]

29

V o l u m e

o f C O 2

Time





In the presence of an acid, potassium iodide reacts with oxygen to give iodine and

water. The reaction rate of this reaction was measured at several temperatures in order

to investigate the effect of temperature on the rate of reaction.

(a) Write a balanced ionic equation for the above reaction.

(b) Outline the procedure of an experiment, which can be used to investigate the

effect of temperature on reaction rate of the reaction by titrimetric analysis.

(c) (i) Sketch a graph showing the relationship between the reaction rate and

temperature. (Label the axes clearly.)

(ii) Explain whether the graph is a straight line or an exponential curve.

[10M]

30

The reaction between ammonium chloride and sodium nitrite in aqueous solution can

be represented by the following equation.

NH4Cl(aq) + NaNO

2(aq) N

2(g) + 2H

2O(l) + NaCl(aq)

The graph below shows the change in volume of nitrogen gas with time from a

mixture of ammonium chloride solution and sodium nitrite solution at 20C.

(a) (i) Describe the change in rate of formation of nitrogen with time. Explain your

answer in terms of collision theory.

(ii) Explain why the volume of nitrogen eventually remains constant.

(iii) What was the maximum volume of nitrogen produced?

(iv) At what time was the reaction half completed?

V o l u m e o f N 2 ( c m

3 )

Time (s)





(b) (i) State and explain any change in the rate of formation of nitrogen if the

temperature was increased from 20C to 40C.

(ii) The reaction between solid ammonium chloride and aqueous sodium nitrite

can be represented by the following equation.

NH4Cl(s) + NaNO

2(aq) N

2(g) + 2H

2O(l) + NaCl(aq)

State and explain any difference in the rate of formation of nitrogen if the

same amount of solid ammonium chloride was used in the form of large

lumps instead of fine powder.

[10M]

Section 39.5

31

A student found that colourless gas bubbles were evolved when a raw egg (with

eggshell) was immersed in vinegar.

(a) Write an equation to show the chemical reaction involved.

(b) The student did the following experiments to investigate the rate of reaction

between eggshell and vinegar. Each experiment was done by adding eggshell to

vinegar in a conical flask and measuring the decrease in mass of the reaction

mixture with time.

Experiment Reaction conditions

1 3 g of eggshell fragments + 50 cm3 of 2.0 M vinegar 25C

2 3 g of eggshell powder + 50 cm3 of 2.0 M vinegar 25C

3 3 g of eggshell powder + 50 cm3 of 2.0 M vinegar 50C

Sketch, on the same graph, the three curves obtained from the experiments.

(c) Explain the differences in the initial rates between

(i) Experiments 1 and 2.

(ii) Experiments 2 and 3.

[11M]

32

Sulphuric acid reacts with zinc powder to form zinc sulphate and hydrogen gas.(a) Write a balanced ionic equation for the above reaction.

(b) Explain the effect of concentration of reactants on reaction rate.

(c) State and explain the effect of adding the following chemicals on the

concentration of hydrogen ions and the rate of production of hydrogen gas.

(i) Adding solid sodium carbonate

(ii) Adding potassium sulphate solution

(iii) Bubbling hydrogen chloride gas

(d) Explain any difference in the rate of the reaction if the same mass of zincgranules is used instead of zinc powder at the same temperature and pressure.





[15M]

33

A student took a lump of limestone (calcium carbonate) weighing exactly 1 g and

dissolved it in an excess amount of hydrochloric acid. The gas given off during this

reaction was collected and its volume was measured at regular time intervals. The

experiment was repeated using small fragments of limestone. The table below gives

the results:

Time (min)Experiment A

Volume of gas (cm3)

Experiment B

Volume of gas (cm3)

0 0 0

1 11.0 18.5

2 22.0 37.5

3 33.0 54.5

4 43.5 67.5

5 53.5 74.5

6 63.0 78.5

7 71.0 80.0

8 77.5 80.0

9 79.5 80.0

10 80.0 80.0

11 80.0 80.0

12 80.0 80.0

(a) The experiment was designed to show the effect of using solid particles with

different surface areas. Suggest TWO factors that should be kept constant in

these experiments.

(b) Plot, on the same graph, the rate curves obtained from experiments A and B.

State which experiment used a lump of limestone.

(c) With reference to the results of these experiments, explain the following

phenomena briefly.

(i) Aluminium foil can be stored safely but containers of aluminium dust carry

the hazard warning ‘DUST EXPLOSION POSSIBLE’.

(ii) Twigs are better for lighting fires than logs.

[9M]

34

When excess lumps of magnesium carbonate are added to dilute hydrochloric acid,

the following reaction takes place.

MgCO3(s) + 2HCl(aq) MgCl2(aq) + CO2(g) + H2O(l)(a) Suggest TWO ways to study the rate of this reaction. In each case sketch a graph





to show the change in the value of the chosen variable with time.

(b) State and explain TWO ways in which the rate of the reaction can be increased.

(c) State and explain whether the total volume of carbon dioxide gas produced

would increase, decrease or remained unchanged if

(i) more lumps of magnesium carbonate were used.

(ii) the experiments were carried out at a higher temperature.

[12M]

35

30 g of Na2S2O3 granules reacted with 250 cm3 of 0.50 M I2 solution.

(a) Write a balanced ionic equation for this reaction.

(b) Which of the reactants is the limiting reagent?

(c) Suggest TWO methods to increase the rate of the reaction.

(d) What physical property can be measured to monitor the reaction?

[7M]

36

A student carried out five experiments to investigate the factors affecting reaction rate

of the reaction between magnesium and dilute hydrochloric acid. Five rate curves

were obtained from these experiments. Magnesium metal is in excess in the five

experiments. The table below shows the experimental conditions in each experiment.

Experiment 1 2 3 4 5

Volume of HCl (cm3) 20 75 70 70 50

Concentration of HCl (M) 2.0 2.0 3.0 3.0 3.0

Temperature of HCl (

C) 20 35 50 35 35

Size of Mg ribbons granules powder granules powder

(a) Explain why sodium is not used to carry out the experiment.

(b) Assign the following rate curves to their corresponding experiments.

V o l u m e o f H 2 ( g )

Time





(c) Explain the following phenomena briefly.

(i) Slaked lime that used to neutralize acid soils is usually in powdered form.

(ii) Ingredients of soup are usually cut into small pieces.

(iii) Food can be kept longer in a refrigerator.

[13M]

Section 39.6

37

Excess zinc turnings reacted with 50 cm3 of 2.0 M hydrochloric acid at 20C. State

and explain the effect on initial rate and extent of reaction when

(a) using 50 cm3 of 1.0 M acid instead of 2.0 M acid.

(b) carrying out the reaction at 30C.

(c) adding a few drops of copper(II) sulphate solution to the reaction mixture.

(d) using larger pieces of zinc.

[8M]

38

5 g of zinc granules was put in a conical flask and covered with 100 cm3 (in excess) of

2.0 M hydrochloric acid at 20C. A fairly slow reaction takes place.

Each of the following changes was made to the experiment while other factors were

kept identical.

New conditionChange in reaction

rate, if anyReason

Using 5 g of powdered

zinc

Using 3 g of zinc

granules

[Remarks: Assume that

the size of granules

remains unchanged.]

Using 100 cm3

of 2.0 Methanoic acid

Changing the temperature

to 40C

Adding a few drops of

aqueous copper(II) nitrate

Simply state in the table whether you would expect the rate to be increased, decreased

or unchanged, and in each case give a reason for your answer.

[10M]39





2H2O2(aq) 2H2O(l) + O2(g)

(a) Suggest a method to monitor the rate of production of oxygen gas.

(b) The following graph shows the change in volume of oxygen gas with time:

Suggest TWO methods to increase the initial rate of the reaction.

(c) Sketch, on the graph in part (b), the curve that should be obtained after one of the

methods you suggested in part (b) is used. Label the new curve as ‘c’. (Assume

that the volume of oxygen gas collected is the same as before.)

(d) A student found that liver extracts can catalyze the decomposition of H2O2(aq).

He studied the change in activity of the biological catalyst involved with

temperature.

Explain his finding with your knowledge about biological catalyst.

[8M]

42

You are a consultant for a chemical company which manufactures ammonia as their

products. John, the manager of the company, wants to increase the rate of production

of ammonia. He would like to ask for your advice.

(a) Write a balanced chemical equation for the synthesis of ammonia. Give the name

V o l u m e o f o x y g e n g a s

Time

I n c r e a s e i n r e a c t i o n r a t e ( M s

1 )

Temperature (C)37 80





of the catalyst used.

(b) Briefly describe the collision theory. Use the theory to explain the rate of a

chemical reaction.

(c) State how the rate of a reaction relates to collision theory.

(d) Given that catalysts can lower the minimum ‘energy barrier’ for the reaction to

occur, explain why catalysts can increase reaction rate the collision theory.

(e) John stated that the company can save the cost of production by applying a

catalyst since the yield of reaction is increased. Comment on his statement.

[12M]

43

Catalysts have characteristic effects in chemical reactions and they are important in

modern chemistry. Answer the following questions about catalysts.

(a) What is a catalyst?

(b) Explain why the iron used in Haber process should be finely divided?

(c) Name the catalyst used in Contact process. Give the oxidation state of the metal

in this catalyst.

(d) A student made the following statement about enzyme:

‘Browning of some fruits and vegetables is caused by the presence of enzymes

produced by the cells. These enzymes react with ingredients of the fruits and

vegetables to form a brown substance.’

Comment on his statement.

(e) Give TWO applications of enzyme in industry.

[11M]

Chemistry: Chapter 40 Molar volume of gases at room temperature and pressure

(r.t.p.)

Sections 40.140.2

44The following graph represents the results of three experiments involving the reaction

of magnesium and dilute hydrochloric acid.





Answer the following questions, giving a reason for each of your answers.

(d) ess, V cm3 of M mol dm3 hydrochloric

(i) ith molarity

(a) Which experiment has the highest initial rate?

(b) Which experiment uses the most concentrated acid?

(c) Which experiment produces the largest volume of gas?

Given that magnesium was used in exc

acid was used in Experiment 2 at 25C.

Find the volume of the acid w2

M mol dm3, in terms of V ,

(ii) Suggest TWO suitable conditions for Experiment 1.

[10M]

:

O

(a) ition of hydrogen peroxide.

(IV) oxide.

(ii) state the

(iii) e and collect oxygen produced

(b) cm3 of 2.0 M hydrogen peroxide

(i) oles of hydrogen peroxide in 100 cm3 of 2.0 M

2) formed.

needed in Experiment 3.

45

Consider the following reaction

2H2 2(aq) 2H2O(l) + O2(g)

Oxygen can be prepared by the catalytic decompos

This reaction is catalysed by manganese

(i) Explain the term ‘decomposition’.Given that manganese(IV) oxide increases the rate of reaction,

criteria to be fulfilled to show that it is a catalyst for this reaction.

Draw the set-up that could be used to prepar

by the decomposition of hydrogen peroxide.

At room temperature and pressure, 100

decomposed in the presence of a catalyst.

Calculate the number of m

hydrogen peroxide.(ii) Calculate the number of moles of oxygen (O

V o l u m e o f g a s p r o

d u c e d ( c m

3 )

Time (s)

1

2

3





(iii) Calculate the volume of oxygen produced.

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, producing carbon dioxide

(b) he volume of carbon dioxide produced and the volume of oxygen

remained.

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unreacted O2 occupied 2.0 cm3. Calculate

the composition of the mixture by volume.

[4M]

lecular formula of A.

(All volumes were measured at room temperature and pressure.)

[4M]

drogen

.)

sent in the airship.

(d) ume of oxygen, calculate the volume of air

required to complete the reaction.

[6M]

The volumes of gas produced during the reaction are recorded and listed

below:

46

100 cm3 of ethene, C2H4, was burnt in 400 cm3 of oxygen

and some liquid water. Some oxygen remained unreacted.

(a) Write the equation for the complete combustion of ethene.

Calculate t

47

An industrial chemist who works for a firm which manufactures ethyne (C2H2)

discovers a very cheap way of producing ethyne. Unfortunately, the ethyne is

contaminated with ethene. Unless the mixture contains at least 50% by volume of

ethyne, it is useless. In order to determine the relative proportions of the two gases in

the mixture, he exploded 10.0 cm3 of the mixture with 30.0 cm3 of oxygen. After

absorbing the residual CO2 with KOH, the

48

When 20.0 cm3 of a gaseous hydrocarbon A was exploded with 150 cm3 of oxygen,

the residual gases occupied 110 cm3. After shaking the residual gases with aqueous

sodium hydroxide, the final volume was 30.0 cm3. Deduce the mo

49

Suppose an airship was filled with 4.80 × 103 dm3 of hydrogen gas initially at r.t.p. In

an accident, the hydrogen gas inside the airship was ignited and all of the hy

gas reacted with oxygen in air to form water. (Density of water is 1.0 g cm3

(a) Calculate the number of moles of hydrogen gas pre(b) Write a balanced equation for the above reaction.

(c) Calculate the volume of oxygen consumed and water formed at r.t.p.

Suppose air contains 21% by vol

50

Consider the reaction between excess calcium carbonate and dilute hydrochloric acid

at r.t.p.





Time (s) 5 10 15 20 25 30 35

Volume of gas produced (cm3) 10 15 18 19 20 20 20

(a) Write a balanced equation for the reaction involved.

(b) Given that the molar volume of any gas at r.t.p. is 24.0 dm3

mol1

, draw a table toshow the number of moles of gas produced at different times.

(c) Plot a graph of number of moles of gas produced against time.

[5M]

51

200 cm3 of hydrogen reacts with 200 cm3 of oxygen to give water as the only product.

(All volumes are measured at r.t.p.)

(a) Write a balanced chemical equation for the reaction.

(b) What is the excess volume of oxygen?

[4M]

52

45 cm3 of ammonia gas (NH3) was mixed with 60 cm3 of hydrogen bromide gas (HBr)

to give ammonium bromide (NH4Br), a white solid, as the only product.

(All volumes are measured at r.t.p.)


(b) What is excess volume of hydrogen bromide gas?

[4M]

53

The following graph shows the volume of oxygen against time when 24.0 cm3 of

hydrogen was combusted with 12.0 cm3 of oxygen.

2H2(g) + O2(g) 2H2O(g)





(a) Calculate the initial rate (in cm3 min1) of oxygen gas consumed in the reaction.

(b) Calculate the average rate (in cm3 min1) of oxygen gas consumed in the

reaction.

(c) (i) What was the total volume of gases when the reaction was complete?

(ii) Calculate the overall percentage change of volume of the gases in the

reaction.[7M]

54

Hydrogen peroxide decomposes at r.t.p. according to the following equation:

2H2O2(aq) 2H2O(l) + O2(g)

(a) Describe ONE method to determine the rate of the above reaction.

(b) At the end of the reaction, 100 cm3 of 1.0 M hydrogen peroxide solution gives

oxygen of percentage yield 86.7%. Calculate the volume of oxygen produced in

cm3.

(c) Name a catalyst for this reaction.

V o l u m e o f O 2 ( c m

3 )

Time (min)





[7M]

Section 40.3

55

Sulphur dioxide is usually found in the exhaust gas produced by combustion of fossil

fuels. It is one of the major sources of acid rain which causes corrosion to objects

containing calcium carbonate.

(a) Write the chemical equation(s) to explain the formation of acid rain by sulphur

dioxide.

(b) Write a chemical equation to explain the corrosion of marble by acid rain.

(c) It is found that 1600 dm3 of sulphur dioxide at r.t.p. is produced by a car every

day. If all the amount of sulphur dioxide produced is involved in the formation of

acid rain, calculate the mass of calcium carbonate corroded by the acid rain

containing such amount of sulphur dioxide.

[7M]

56

Hydrocarbons undergo complete combustion to give carbon dioxide under sufficient

oxygen supply. Toxic carbon monoxide is produced if the oxygen supply is

insufficient. Catalytic converters are usually installed in vehicles to minimize the

emission of carbon monoxide in exhaust gas.

(a) (i) Balance the following equation:

CH3CH2CH3(g) + O2(g) CO2(g) + CO(g) + H2O(l)

(ii) Suppose 4.95 g of propane (CH3CH2CH3) gas is introduced. What is the

volume of carbon monoxide produced at r.t.p. from the above incomplete

combustion?

(b) Inside the converter, carbon monoxide is converted to carbon dioxide in the

presence of oxygen. Write a chemical equation for the reaction involved.

(c) (i) What is the volume of oxygen required at r.t.p. to remove the amount of

carbon monoxide calculated in part (a)(ii)?

(ii) Express the amount of oxygen required in g.[8M]

57

The operation of automobile airbags depends on the rapid decomposition of sodium

azide, NaN3, to its elements.

(a) Write a balanced equation for this decomposition.

(b) If an airbag has a volume of 5.20 × 104 cm3, calculate the number of moles of

nitrogen gas required to fill it at room temperature and pressure.

(c) Calculate the mass of sodium azide needed to provide such volume of nitrogen.

(d) If the decomposition is complete in 40 ms, calculate the average rate of





formation of nitrogen in dm3 s1.

[5M]

58

It is required to find the composition by volume of a sample of Town gas which

contains only hydrogen, carbon monoxide and nitrogen. At room temperature and

pressure, 40.0 cm3 of the Town gas was carefully exploded with 40.0 cm3 of oxygen

(known to be in excess), so that only hydrogen and carbon monoxide would react with

oxygen. On cooling to room temperature, the volume was 51.0 cm3. After adding

concentrated KOH, the volume decreased to 41.0 cm3.

(a) Write equations (including state symbols) for the reactions which occurred on

explosion.

(b) Calculate the volume of CO2 produced.

(c) Calculate the volume of CO in the original 40.0 cm3 of Town gas.

(d) Find the total change in volume as a result of the explosion.

(e) Calculate the decrease in volume which is caused by

(i) CO

(ii) H2

on explosion.

(f) Find the volumes of

(i) H2

(ii) N2

in the original 40.0 cm3 of Town gas.

[10M]

59

In an experiment to investigate the rate of a reaction, a sample of calcium was reacted

with an excess amount of water at room temperature and pressure. Hydrogen gas was

given off and the volumes obtained at different various times were shown in the

following table below.

Time (min) 0 1 2 3 4 5 6

Volume of hydrogen gas (cm3) 0 29 44 53 59 60 60

(a) Draw an experimental set-up which is suitable for carrying out this experiment.

(b) Plot a graph of volume of hydrogen gas against time. Label the curve as ‘ X ’.

(c) Explain why the first part of the graph is the steepest.

(d) Explain why the last part of the graph is a horizontal line.

(e) At what time was the reaction half completed?

(f) Sketch, on the same graph, the curves that would be obtained if only the





following changes were made to the original conditions respectively.

(i) The reaction temperature was 40C. Label this curve as (i).

(ii) Half the original mass of calcium was used. Label this curve (ii).

(g) Using the information given on curve X , calculate the mass of calcium used in

the original experiment.

(h) Calcium also reacts with hydrochloric acid to form hydrogen. If the same mass

of calcium as in part (g) was used to react with excess hydrochloric acid, state

the volume of hydrogen that would be formed. Explain why the rate of reaction

of calcium with hydrochloric acid is higher than that of calcium with water.

[15M]

60


Mg3 N2(s) + 6H2O(l) 3Mg(OH)2(s) + 2NH3(g)

(a) What is the mass of magnesium nitride needed to produce 116.6 g of magnesium

hydroxide?

(b) What volume of ammonia is formed at r.t.p. using the amount of magnesium

nitride specified in part (a)?

(c) What volume of 2.0 M hydrochloric acid is needed to neutralize all the ammonia

gas formed in part (b)?

[8M]

61

Ethyne gas (C2H2) can be produced from the reaction between calcium carbide (CaC 2)

and water, which gives calcium hydroxide as the only side product.


(b) Find the mass of calcium carbide required to prepare 650 cm3 of ethyne at r.t.p.

(c) What volume of hydrogen is needed to convert 650 cm3 ethyne into ethane by

hydrogenation?

[6M]

62Consider the decomposition of 3.00 g of an alloy composed of sodium and lead with

water:

2Na/Pb(s) + 2H2O(l) 2NaOH(aq) + H2(g) + 2Pb(s)

144 cm3 of hydrogen gas was collected at r.t.p. at the end of the reaction.

(a) Calculate the volume of 0.5 M hydrochloric acid required to neutralize the

sodium hydroxide produced.

(b) Find the amount (in g) of sodium in 3.00 g of the alloy.

(c) What is the percentage by mass of lead in the alloy?

[6M]





63

The Castle Peak power station burns about 25 000 tonnes of coal each day. The coal

contains 0.6% by mass of sulphur.

(a) Calculate the mass of sulphur burnt each day.

(b) The sulphur burns in oxygen to give sulphur dioxide. Write an equation for the

reaction.

(c) Calculate the

(i) mass;

(ii) volume of sulphur dioxide produced each day from the power station at

r.t.p..

(1 tonne = 1 × 106 g; molar volume of any gas at r.t.p. = 24.0 dm3 mol1.)

[6M]

64

In Brazil, the fuels used in cars are blended with alcohol. Assume that a fuel contains

75% by mass of octane (C8H18) and 25% by mass of ethanol (C2H5OH), and water

vapour is formed after combustion.

(a) Write balanced equations for the combustion of octane and ethanol.

(b) Calculate the volume of oxygen required to completely burn 100 g of the fuel at

r.t.p.

[5M]

65

Ammonia is manufactured by Haber Process industrially.

N2(g) + 3H2(g) 2NH3(g)

An excess amount of N2(g) and 72.0 cm3 of H2(g) were reacted at r.t.p.

(a) Calculate the number of moles of N2(g) used for complete production of NH3(g).

(b) Calculate the volume of NH3(g) produced.

(c) Do you think the value you calculated in (b) can be obtained in a school

laboratory? Give a reason for your answer.

[6M]66

0.70 g of magnesium ribbon was added to a beaker containing excess 0.50 M H2SO4

at r.t.p.

(a) State ONE observation of the reaction.

(b) Write a balanced equation for the reaction.

(c) A student claimed that there was not enough information to calculate the volume

of gaseous product. State whether he is correct or not. If he is correct, state what

other information is needed. If he is incorrect, calculate the volume of the

gaseous product.





[5M]

67

The major components of town gas are hydrogen and methane, which are made from

naphtha, C5H12. Naphtha reacts with steam to form carbon monoxide and hydrogen.

These two gases further react to form methane.

(a) Write balanced equations for the manufacture of hydrogen and methane.

(b) Find the mass and volume (at room temperature and pressure) of methane

formed when 2.8 g of CO and 1.5 g of H2 are allowed to react.

(c) When town gas is passed over heated iron(III) oxide, iron is formed.

(i) Write a balanced equation to show the reaction involved.

(ii) Calculate the volume of H2, measured at room temperature and pressure,

that would be needed in the complete reduction of 100 g of iron(III) oxide.

(iii) Calculate the volume of town gas, measured at room temperature and

pressure, used in the above reduction, assuming that town gas contains 49%

of H2 by volume.

[11M]

68

100 cm3 of ammonia was reacted with excess copper oxide at room temperature and

pressure. Copper and a gaseous product are formed at the end of the experiment.

(a) Write a balanced equation to show the reaction involved.

(b) Calculate

(i) the number of moles of ammonia used.

(ii) the volume of the gaseous product formed.

(c) Calculate the mass of copper oxide reacted with ammonia.

(d) Calculate the number of copper atoms reacted.

[7M]

69

Dilute nitric acid reacts with copper to produce nitrogen monoxide.

(a) Write a balance equation for the reaction.(b) Calculate the volume of nitrogen monoxide obtained by the complete reaction of

100 g of copper with excess dilute nitric acid at room temperature and pressure.

(c) Calculate the number of copper atoms reacted.

(d) Nitrogen monoxide is colourless. However, during the reaction, a brown gas was

evolved.

(i) Explain the above phenomenon with a proper chemical equation.

(ii) Calculate the volume of nitrogen monoxide needed to produce 500 cm3 of

the brown gas.

(iii) Calculate the volume of air, measured at room temperature and pressure,





used in the reaction, assuming that air contains 20% of O 2 by volume.

[10M]

70

Answer the following questions:

(a) Calculate the volume of 1.75 × 1023 CO2 molecules (in dm3) at room temperature

and pressure.

(b) Consider the complete combustion of ethane at r.t.p.:

2C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(l)

The volumes of ethane and oxygen used are 15.0 dm3 and 53.0 dm3 respectively.

(i) Which one of the two reactants is limiting?

(ii) Calculate the number of moles of water formed on half way of the reaction.

(iii) Calculate the total number of moles of gases in the reaction mixture when

the reaction is complete.

[9M]

71

Answer the following questions:

(a) Calculate the volume (in dm3) occupied by 3.24 × 1024 nitrogen atoms at r.t.p..

(b) Consider the following reaction:

2FeO(s) + C(s) 2Fe(s) + CO2(g)

Calculate the volume (in dm3) of carbon dioxide that can be produced if 40 g of

iron(II) oxide is completely reduced by carbon at r.t.p..

(c) Which one, 67.0 dm3 of carbon dioxide or 36.0 dm3 of methane, possesses more

atoms at r.t.p.? Show your answer by calculation.

[8M]

72

25 g of chalk was immersed in excess vinegar at r.t.p. A decrease in mass of 9.59 g

was recorded at the end of the reaction.

(a) Write an equation to show the reaction between chalk and vinegar.

(b) Calculate the volume of gas evolved in dm

3

.(c) Calculate the percentage of purity of the chalk.

(d) Explain why aluminium tanks can be used to transport vinegar although

aluminium is a relatively reactive metal.

[7M]

73

Hydrogen peroxide undergoes self-decomposition to form water and oxygen. At room

temperature and pressure, 102 g of hydrogen peroxide was allowed to decompose in a

closed system. (Density of water = 1.0 g cm3)

(a) Write a balanced equation for the reaction.




(b) Calculate the volume of gas collected.

(c) Calculate the volume of liquid at the end of the reaction.

(d) Calculate the number of molecules at the end of the reaction.

[7M]

kinetics sq

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