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

In an experiment to compare rates of diffusion, a plug of cotton wool soaked in concentrated aqueous ammonia is placed in one end of a long glass tube. A plug of cotton wool soaked in concentrated hydrochloric acid is placed in the other end. Both ends are sealed with bungs.

After a few minutes a white ring forms inside the tube.

A student repeats the experiment three times and records the distance from the ammonia end to the white ring.

State the value in the table that the student has recorded to an incorrect degree of precision.

Explain why that value is recorded to an incorrect degree of precision.

Calculate the mean distance from the ammonia end to the white ring.

Give your answer to one decimal place.

The mean time for the white ring to appear is 198 s.

Use your answer to part (c) to calculate the mean rate of diffusion of the ammonia.

Give your answer in cm/s to three significant figures.

In an experiment to compare rates of diffusion, a plug of cotton wool soaked in concentrated aqueous ammonia is placed in one end of a long glass tube. A plug of cotton wool soaked in concentrated hydrochloric acid is placed in the other end. Both ends are sealed with bungs.

After a few minutes a white ring forms inside the tube.

A student carries out the experiment three times. The white ring forms in a slightly different position each time.

Suggest two reasons for this.

State why the student calculated a mean position rather than using the result of a single experiment.

Name a piece of apparatus the student could use to put equal volumes of the two solutions onto the cotton wool.

The student repeats the experiment using a tube that is twice as long.

Explain one advantage and one disadvantage of using the longer tube.

In an experiment to compare rates of diffusion, a plug of cotton wool soaked in concentrated aqueous ammonia is placed in one end of a long glass tube. A plug of cotton wool soaked in concentrated hydrochloric acid is placed in the other end. Both ends are sealed with bungs.

After a few minutes a white ring forms inside the tube.

The experiment is repeated in a warmer room.

Predict the effect this has on the time taken for the white ring to appear.

Explain your answer.

The white ring always forms nearer to the hydrochloric acid end of the tube than to the ammonia end.

Explain why.

Use the relative atomic masses H = 1, N = 14 and Cl = 35.5.

The experiment is repeated using a tube twice as long, with the same two solutions and at the same temperature.

Predict how the distance from the ammonia end to the white ring compares with the distance measured in the original tube.

Explain your answer.

A student compares the rates of diffusion of ammonia and hydrogen chloride using the apparatus shown in Fig. 1.1.

A plug of cotton wool soaked in concentrated aqueous ammonia is placed in one end of the tube and a plug of cotton wool soaked in concentrated hydrochloric acid is placed in the other. Both ends are then sealed with bungs.

Fig. 1.1

Name apparatus X.

The student leaves the apparatus undisturbed.

Describe what is seen inside the tube after a few minutes.

Explain why both ends of the tube are sealed with bungs.

The student wants to compare the distance travelled by each gas.

State the two measurements the student should take, using the scale shown in Fig. 1.1.

The product forms as a broad band rather than as a sharp line.

Suggest why.