Water & Water Pollution (Cambridge (CIE) IGCSE Chemistry): Alternative to Practical Questions

A student is given a sample of cloudy river water.

The student pours the sample through a filter funnel containing a layer of sand, and collects the water that passes through.

The collected water is clear but has an unpleasant smell.

State what the sand has removed from the water.

State what the sand has not removed.

The student then pours the collected water through a second funnel containing a layer of carbon.

The water leaving the second funnel has no smell.

Explain what this shows about the carbon.

State why the water is still not safe to drink.

State what should be added to the water to make it safe to drink.

The student records the following in a notebook.

The water was clear after filtering, so it was pure.

Explain why this record confuses an observation with a conclusion.

A student is given two samples of water from different sources. One sample has been treated at a water treatment works. The other has been taken from a river.

Plan an investigation to find out which sample contains more dissolved solid.

Your plan should include:

• the apparatus you would use

• the method, including the measurements you would make

• how you would make your results accurate

• how you would use your results to reach a conclusion

A student investigates the purity of two water samples, P and Q.

The student cools each sample in a freezing mixture and records the temperature of the sample every minute until it has frozen.

The student uses a thermometer with a range of −10 °C to +110 °C and 1 °C graduations.

The readings for sample P are shown.

State which reading has been recorded to an incorrect degree of precision.

State how it should have been recorded.

The temperatures at which the two samples froze are shown.

State which sample is pure water.

State the feature of the results that shows this.

Suggest two improvements the student could make in order to obtain more accurate results.

State one variable that the student must keep the same for both samples.

A student is given a colourless liquid, L, and is asked to find out whether it contains water.

The student has anhydrous copper(II) sulfate and anhydrous cobalt(II) chloride available.

Describe what the student should do with the anhydrous copper(II) sulfate.

State what would be seen if L contains water.

State why the copper(II) sulfate used in this test must be anhydrous.

The student then tests liquid L and a second liquid, M, using anhydrous cobalt(II) chloride.

Complete the table by stating the conclusion that can be drawn from each observation.

The student writes the following conclusion.

The solid turned pink, so liquid L is water.

Explain why this conclusion is not fully correct.

Name a piece of apparatus the student could use to add a few drops of liquid L to the solid.