Diffusion (Cambridge (CIE) O Level Chemistry): Exam Questions

Concentrated ammonia solution gives off ammonia gas. Concentrated hydrochloric acid gives off hydrogen chloride gas. Ammonia, NH₃, and hydrogen chloride, HCl, are both colourless gases. Ammonia reacts with hydrogen chloride to make the white solid ammonium chloride.

Apparatus is set up as shown.

After ten minutes a white solid forms in the tube where the gases meet.

i) Write the chemical equation for the reaction of ammonia with hydrogen chloride.

[1]

ii) Name the process by which the ammonia and hydrogen chloride gases move in the tube.

[1]

iii) At which point, A, B, C or D, does the white solid form? Explain why the white solid forms at that point.

[3]

iv) The experiment was repeated at a higher temperature. Predict how the results of the experiment would be different. Explain your answer.

[3]

Some of the white solid is removed from the tube and dissolved in water.

Describe how the white solid could be tested to show it contains:

i) Ammonium ions.

Test ...........................
Result .......................

[3]

ii) Chloride ions.

Test .........................
Result .....................

[3]

The diagram shows the electron arrangement in a molecule of ammonia, showing only outer shell electrons.

i) State the type of bonding in ammonia.

[1]

ii) Hydrazine, N₂H₄, is another compound of nitrogen and hydrogen. Complete the diagram to show the electron arrangement in a molecule of hydrazine, showing only outer shell electrons.

[3]

Nylon and proteins are both polymers containing nitrogen.

i) Name the linkages found in the polymers of nylon and protein.

[1]

ii) Describe one difference in the structures of nylon and protein.

[1]

iii) What is the general name given to the products of hydrolysis of proteins?

[1]

Suggest the structure of the monomer used to make the polymer shown.

Two identical balloons are filled to the same size. One is filled with helium and the other is filled with air.

The rubber of each balloon contains very small holes.

After two days the helium balloon has shrunk noticeably. The air-filled balloon has hardly changed in size.

relative atomic mass of helium = 4

average relative molecular mass of air = 29

Use the data to explain why the helium balloon shrinks faster.

State one variable that must be kept the same if the comparison between the two balloons is to be fair.

The experiment is repeated using a balloon filled with argon in place of the helium.

relative atomic mass of argon = 40

Predict how the rate at which argon diffuses out of the balloon compares with the rate at which air diffuses in.

Explain your answer.

An average relative molecular mass is quoted for air, rather than a single exact value.

Suggest why.

Natural gas has no smell of its own. A small amount of a strongly smelling gas, called an odourant, is added to it so that leaks can be noticed.

Two odourants are tested. A small amount of each is released at one end of a room. The time taken for the smell to be noticed 12 m away is recorded.

Using the table, state which odourant is noticed sooner.

Explain, in terms of the particles, why that odourant is noticed sooner.

A third odourant, Z, has a relative molecular mass of 76.

Predict how the time taken for the smell of Z to be noticed 12 m away would compare with the times in the table.

Both tests were carried out at the same temperature.

Explain why this is important.

A student places a small crystal of a purple dye at the bottom of a beaker of water and measures the time taken for the colour to spread 8 cm up the beaker.

The student repeats the experiment at three temperatures.

Describe the trend shown by the results.

Explain the trend using kinetic particle theory.

Predict the time it would take for the colour to spread 8 cm if the experiment were repeated at 30 °C.

The student was careful not to stir the water at any point during the experiment.

Explain why.

Nitrogen, N₂, and ethene, C₂H₄, are both colourless gases.

Calculate the relative molecular mass, M_r, of nitrogen and of ethene.

Use the relative atomic masses H = 1, C = 12 and N = 14.

Both gases are held at the same temperature.

Predict which of the two gases diffuses faster.

Explain your answer.

A third colourless gas, carbon monoxide, CO, is also tested at the same temperature.

Calculate the relative molecular mass of carbon monoxide.

Use the relative atomic masses C = 12 and O = 16.

Nitrogen, ethene and carbon monoxide contain different elements and have different chemical properties.

Suggest what these three gases show about using relative molecular mass to predict the rate of diffusion of a gas.

A small amount of liquid bromine is added to a container which is then sealed.

Br₂(l) → Br₂(g)

Use the ideas of the Kinetic Theory to explain why, after about an hour, the bromine molecules have spread uniformly to occupy the whole container.

The diagrams below show simple experiments on the speed of diffusion of gases.

Complete the following explanations. Diagram 1 has been done for you.

Diagram 1 There is air inside and outside the porous pot so the rate of diffusion of air into the pot is the same as the rate of diffusion of air out of the pot. The pressure inside and outside the pot is the same so the coloured liquid is at the same level on each side of the tube.

Diagram 2.

................................

Diagram 3

................................

Acid-base reactions are examples of proton transfer.

Ethylamine is a weak base and sodium hydroxide is a strong base.

i) In terms of proton transfer, explain what is meant by the term weak base.

[2]

ii) Given aqueous solutions of both bases, describe how you could show that sodium hydroxide is the stronger base. How could you ensure a ‘fair’ comparison between the two solutions?

[3]

Ethylamine reacts with acids to form salts.

CH₃CH₂NH₂      +     HCl    →   CH₃CH₂NH₃Cl

                                                                ethylammonium chloride

i) Complete the equation for the reaction between sulfuric acid and ethylamine. Name the salt formed.

......  CH₃CH₂NH₂       +       ............     →     .........................

Name of salt ........................................................................

[3]

ii) Amines and their salts have similar chemical properties to ammonia and ammonium salts.

Suggest a reagent that could be used to displace the weak base, ethylamine, from its salt ethylammonium chloride.

[1]

Gases diffuse, which means that they move to occupy the total available volume.

i) Explain, using kinetic particle theory, why gases diffuse.

[2]

ii) When the colourless gases hydrogen bromide and ethylamine come into contact, a white solid is formed.

CH₃CH₂NH₂ (g) + HBr (g)     →     CH₃CH₂NH₃Br (s)

     white solid

The following apparatus can be used to compare the rates of diffusion of the two gases ethylamine and hydrogen bromide.

Predict at which position, A, B or C, the white solid will form. Explain your choice.

[3]

Different gases diffuse at different speeds.

i) What is meant by the term diffusion?

[1]

ii) What property of a gas molecule affects the speed at which it diffuses?

[1]

Helium is a gas used to fill balloons. It is present in the air in very small quantities. Diffusion can be used to separate it from the air. Air at 1000°C is on one side of a porous barrier. The air which passes through the barrier has a larger amount of helium in it.

i) Why does the air on the other side of the barrier contain more helium?

[1]

ii) Why is it an advantage to have the air at a high temperature?

[1]

Most helium is obtained from natural gas found in the USA. Natural gas contains methane and 7% helium. One possible way to obtain the helium would be to burn the methane.

i) Write an equation for the complete combustion of methane.

[1]

ii) Suggest why this would not be a suitable method to obtain the helium.

[1]

iii) Suggest another method, other than diffusion, by which helium could be separated from the mixture of gases in natural gas.

[1]

Kinetic theory explains the properties of matter in terms of the arrangement and movement of particles.

Nitrogen is a gas at room temperature. Nitrogen molecules, N₂, are spread far apart and move in a random manner at high speed.

i) Draw the electronic structure of a nitrogen molecule. Show only the outer electron shells.

[2]

ii) Compare the movement and arrangement of the molecules in solid nitrogen to those in nitrogen gas.

[3]

A sealed container contains nitrogen gas. The pressure of the gas is due to the molecules of the gas hitting the walls of the container.

Use the kinetic theory to explain why the pressure inside the container increases when the temperature is increased.

The following apparatus can be used to measure the rate of diffusion of a gas.

The following results were obtained.

i) Explain why nitrogen gas diffuses faster than chlorine gas.

[2]

ii) Explain why the nitrogen gas diffuses faster at the higher temperature.

[1]

Chlorine and bromine are both in Group VII of the Periodic Table.

A sample of chlorine gas and a sample of bromine vapour are released into separate identical tubes at the same temperature.

relative atomic mass of chlorine = 35.5

relative atomic mass of bromine = 80

State which of the two diffuses faster.

Explain your answer to part (a).

A student explains the difference by writing:

"The two gases diffuse at different rates because chlorine and bromine have different relative atomic masses."

The relative atomic masses are different, but the explanation does not gain credit.

Explain why not.

A second student suggests that the gases diffuse at different rates because chlorine is more reactive than bromine.

Explain why this suggestion is not correct.

This question is about ammonium compounds.

The table shows the names and formulae of some ammonium compounds. 

i) Complete the table by giving the missing information. 

[2]

ii) When ammonia reacts with nitric acid, ammonium nitrate is formed. 

Write a chemical equation for this reaction. 

[1]

When ammonium chloride is heated, it undergoes thermal decomposition to form two gaseous products.

Describe the result of testing each product with damp universal indicator paper.

The diagram shows the apparatus used to heat ammonium chloride.

i)

Suggest why both a red and a blue litmus paper are used.

[1]

ii)

Explain what happens to the damp litmus paper as the ammonium chloride is heated.

[3]

Explain why a fine white powder formed on the inside of the neck of the conical flask.