3.2 Water

Question 1

What is in temporary hard water but not in permanent hard water?

Answer 1

Hydrogencarbonate ions

Question 2

What happen when temporary hard water is boiled?

Answer 2

The hydrogencarbonate ions decompose to form calcium carbonate (limestone). This is the limescale on kettles.

Question 3

What are the advantages of hard water?

Answer 3

Calcium ions are good for teeth and bones. Less likely to develop heart disease.

Question 4

What are the disadvantages of hard water?

Answer 4

More expensive as more soap is needed. Boiling temporary hard water produces scale, this reduces the efficiency of heating systems.

Question 5

How can hard water be softened?

Answer 5

Soft water can be softened by boiling. Both types can be softened by adding sodium carbonate. Both types can be softened by running the water through ion exchange columns.

Question 6

What ions does hard water contain?

Answer 6

Ca₂₊ and Mg₂₊

Question 7

How is water purified?

Answer 7

Mesh screen to remove big objects, chemicals to make solids stick together, filtered through gravel to remove the solids, chlorinated to kill bacteria

Question 8

What are the advantages of adding chloride and fluoride to water?

Answer 8

Reduces microbes, reduces tooth decay.

Question 9

What are the disadvantages of adding chloride and fluoride to water?

Answer 9

Might cause/increase risk of some cancers and bone problems.