Potable water

Desalination is the removal of salt from seawater to produce drinking water.

The seawater is heated and the water vapour condensed and collected.

Which separation technique is used to produce drinking water in desalination?

A Chromatography

B Crystallisation

C Distillation

D Filtration

Chlorine is an element found in Group 7 of the Periodic Table.

What are the elements in Group 7 called?

Tick (✓) one box.

Why is chlorine found in Group 7 of the Periodic Table?

Use ideas about electron arrangement.

The diagram shows the reaction between a small piece of hot sodium and chlorine gas.

The sodium burns with a bright yellow flame and a white solid is produced.

What is the name of the white solid made in the reaction?

A student thinks that the experiment is unsafe.

How could the experiment be improved to make it safe?

The metal spoon is made from an alloy of copper.

Suggest a property of this alloy which makes it suitable to use in the experiment.

The Group 7 elements can be placed into an order of reactivity by using displacement reactions.

The table shows the results of mixing three Group 7 elements, X, Y and Z, and solutions of their salts.

Key ✓ = reaction ✗ = no reaction

Describe how the reactivity of the Group 7 elements changes going down the group.

Use the Periodic Table.

Which of the elements X, Y or Z is chlorine?

Which statements about the reactivity of the Group 7 elements are true, and which are false ?

Tick (✓) one box in each row.

This diagram shows how water is treated so it is safe to drink.

At which stage, 1–4, is chlorine added to water?

Why is chlorine added to water?

A student does some experiments to separate water from muddy water.

Fig. 11.1 shows the equipment the student uses in their first experiment.

Fig. 11.1

What is the name of this separation technique?

The water produced in the experiment is a very light brown colour.

Why is the student not sure that the water produced is potable ?

Tick (✓) two boxes.

Fig. 11.2 shows the equipment the student uses in their second experiment.

Fig. 11.2

The student leaves the equipment in a sunny place.

The statements describe how the experiment produces water.

The statements are not in the correct order.

A The water drips into the beaker.

B The sun heats up the muddy water.

C The water evaporates.

D The water vapour cools and condenses.

E The water vapour rises upwards.

F The water vapour touches the cold piece of glass.

Write the remaining letters in the boxes to show the correct order of the statements.

Which Group 7 element is most often added to tap water to make it potable?

A Bromine

B Chlorine

C Fluorine

D Iodine

Drinking water that comes from lakes and reservoirs must be made safe to drink.

Which name is given to water that has been made safe to drink?

Tick (✓) one box.

Water can also be purified by simple distillation.

The diagram shows the equipment used by a student to distil sea water.

Give two reasons why this equipment is not suitable to produce water on a large scale.

On average one person in the UK uses 149 litres of water every day.

Only 3% of this water is used for drinking.

Calculate the amount of drinking water a family of four uses every day.

Give your answer to 3 significant figures.

Amount of drinking water =........ litres

Large scale desalination is used to make drinking water from seawater in hot countries.

What is the name of the technique used to remove the dissolved salts from seawater to get drinking water?

A Chromatography

B Evaporation

C Filtration

D Simple distillation