Potable water

Water treatment is needed to make most sources of water suitable for drinking.

Water treatment includes the processes of chlorination, filtration and sedimentation.

Place these processes in the order that they take place during water treatment.

Some tap water contains chloride ions.

Explain, in terms of electrons, how a chlorine atom, C l, forms a chloride ion, Cl^–.

Why is chlorine added to water during water treatment?

State why tap water is not suitable for use in chemical analysis.

A student was asked to distil a sample of tap water. Figure 4 shows the apparatus the student used.

The student made an error when setting up the apparatus in Figure 4.

This error meant that pure water could not be collected in the test tube.

Explain what the student needs to change so that pure water can be collected in the test tube.

State what the student should use to heat the water.

Potable water is water that is suitable for drinking.

River water can be treated to make it potable. Chlorination, filtration and sedimentation are three of the processes involved in making the river water potable.

Which row of the table shows these three processes in the order in which they are carried out?

State the reason why chlorine is added during the water treatment.

Describe how sedimentation is carried out.

Figure 3 shows the results of an analysis of a sample of potable water.

Using this information, explain why this sample of potable water is not the same as pure water.

A student wanted to distil a sample of potable water. Figure 4 shows apparatus the student used.

Name the piece of equipment labelled X in Figure 4.

The student made an error when setting up the equipment in Figure 4. This error meant no water could be collected in the test tube.

Explain what the student needs to do so water can be collected.

A sample of potable water contains impurities.

Why is this sample of water potable even though it contains impurities?

Waste water can be used to produce drinking water. The processes used include sedimentation, filtration and chlorination.

What is sedimentation?

State why the waste water is filtered.

State the reason for chlorination.

Some salts can be added to waste water to remove impurities. In an experiment, different masses of salt A were added to 1000cm³ samples of waste water. The experiment was repeated with salt B. The percentages of impurities removed from the waste water are shown in Figure 7.

mass of salt in mg per 1000cm³ water

Figure 7

It was concluded that the best way to purify 1000cm³ of the waste water is to add 100 mg of salt B.

Use the information about salt A and salt B in Figure 7 to evaluate this conclusion.

*(d) A sample of water was contaminated with a dissolved solid.

Devise a plan to separate pure water from this mixture, including a test to show that the water obtained is neutral.

You may use some or all of the apparatus shown in Figure 8 and any other laboratory apparatus.

A sample of potable water contains impurities.

Why is this sample of water potable even though it contains impurities?

Waste water can be used to produce drinking water. The processes used include sedimentation, filtration and chlorination.

What is sedimentation?

State why the waste water is filtered.

State the reason for chlorination.

Some salts can be added to waste water to remove impurities. In an experiment, different masses of salt A were added to 1000cm³ samples of waste water. The experiment was repeated with salt B. The percentages of impurities removed from the waste water are shown in Figure 3.

mass of salt in mg per 1000cm³ water

Figure 3

It was concluded that the best way to purify 1000cm³ of the waste water is to add 100 mg of salt B.

Use the information about salt A and salt B in Figure 3 to evaluate this conclusion.

Waste water may contain phosphate ions, PO₄^3-.

Aluminium ions react with phosphate ions to form aluminium phosphate.

Complete the ionic equation for the formation of aluminium phosphate in this reaction.

_........ + PO₄^3- _........

Which of the following substances will be a solid at 20 C and will melt when placed in a beaker of hot water at 80 C?

A student set up the apparatus shown in Figure 2 to obtain pure water from sea water by distillation.

Explain how the water in sea water separates to produce the pure water in this apparatus.

Explain how the apparatus could be improved to increase the amount of pure water collected from the same volume of sea water.

A substance is heated at a constant rate and its temperature is taken every minute. During the heating, the substance undergoes one change of state.

The results are shown on the graph in Figure 3.

Explain the shape of the graph in terms of the changes in the movement and arrangement of the particles as the substance is heated.