Solids, liquids & gases (Cambridge (CIE) IGCSE Chemistry): Alternative to Practical Questions

A student is given a sample of a colourless liquid, L.

L boils at a temperature below 100 °C.

Plan an experiment to determine the boiling point of L.

Your plan must include the use of common laboratory apparatus and the sample of L. No other chemicals should be used.

Your plan must include:

• the apparatus needed

• the method to use and the measurements to take

• procedures to ensure that the boiling point determined is as accurate as possible

• how the measurements are used to determine the boiling point

You may draw a diagram to help answer the question.

A student investigates how the volume of a fixed mass of air changes with temperature.

The student:

• seals a sample of air inside a syringe

• stands the syringe in a water bath

• leaves the syringe in the water bath for five minutes

• records the volume of the air

• repeats the experiment at different water bath temperatures

The results are shown in Table 2.1.

Table 2.1

Name the piece of apparatus the student uses to measure the volume of the air.

Use Table 2.1 to identify the anomalous result.

Suggest what the student should do about the anomalous result.

Ignoring the anomalous result, describe the relationship between the temperature of the air and its volume.

The student leaves the syringe in the water bath for five minutes before recording each volume.

Suggest why.

Suggest two improvements to the student's method that would give more reliable results.

A student determines the melting point of a solid, X.

The student:

• places a sample of solid X in a boiling tube

• melts the solid completely

• places the boiling tube in a rack and allows it to cool

• records the temperature of X every 30 seconds

The results are shown in Table 1.1.

Table 1.1

Name the piece of apparatus the student uses to measure the temperature of X.

The student melts the solid by standing the boiling tube in a beaker of hot water, rather than by heating the boiling tube directly in a Bunsen burner flame.

Suggest two reasons for melting the solid in this way.

The student records all of the temperatures to the nearest 0.5 °C.

One value in Table 1.1 is not recorded to this degree of precision.

State this value.

State the melting point of X.

Explain how you used the results in Table 1.1 to decide.

The student repeats the experiment using a sample of X that contains an impurity.

Describe two ways in which the results for the impure sample are different.

Suggest one improvement to the student's method that would give a more accurate value for the melting point of X.

A student investigates how the pressure applied to a fixed mass of air affects its volume.

The student:

• seals a sample of air inside a gas syringe

• connects the syringe to a pressure gauge

• pushes the plunger in by a small amount and waits for the reading to settle

• records the pressure and the volume of the air

• repeats until five pairs of readings have been taken

The temperature of the air is kept the same throughout.

The results are shown in Table 5.1.

Table 5.1

Use Table 5.1 to describe how the volume of the air changes as the pressure increases.

Extended Tier Only

Explain, in terms of the air particles, why the volume of the air decreases as the pressure increases.

The student repeats the measurement at 140 kPa twice more, obtaining volumes of 43.0 cm³ and 42.0 cm³.

Calculate the mean volume of the air at 140 kPa, using all three results.

The student keeps the temperature of the air the same throughout the investigation.

Explain why the results would be misleading if the temperature of the air rose while the readings were being taken.

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.

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.

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.

Ammonia gas and hydrogen chloride gas diffuse at different rates.

When the two gases meet they react to form a white solid.

Plan an experiment to compare the rates of diffusion of ammonia and hydrogen chloride.

Your plan must include the use of common laboratory apparatus, concentrated aqueous ammonia and concentrated hydrochloric acid. No other chemicals should be used.

Your plan must include:

• the apparatus needed

• the method to use and the measurements to take

• the variables to control

• how the measurements are used to compare the rates of diffusion

You may draw a diagram to help answer the question.

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.

Extended Tier Only

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.