Water

Question 1

What is in water filters that removes hardness from water? [1]

Answer 1

ion exchange resin

Question 2

Suggest why water filters used in the home contain particles of silver. [1]

Answer 2

prevent growth of microbes

Question 3

Pure water can be produced by distillation.

Why is distillation not usually an economic method of treating water for drinking? [1]

Answer 3

high cost of energy / heating

Question 4

Describe how an ion exchange column softens water. [3]

Answer 4

• calcium ions (in water)…
• …can be replaced by…
• …sodium ions (in resin)

Question 5

Sodium chloride needs to be passed through the ion exchange column.
Suggest why. [1]

Answer 5

to replenish sodium ions (in resin)

Question 6

Suggest one argument for and one argument against water companies adding chlorine to sterilise water. [2]

Answer 6

Argument for:

• prevents diseases
• kills microbes
• only small amounts needed

Arguments against:

• toxic / poisonous
• no consumer choice

Question 7

What are the two main steps used to treat water from reservoirs? Give one reason for each step. [4]

Answer 7

• filter…
• …to remove solids
• (add) chlorine…
• …to reduce the number of microbes

Question 8

State one health benefit of drinking hard water. [1]

Answer 8

• helps to develop / maintain bones
• helps to develop/ maintain teeth
• reduces heart disease

Question 9

Hard water contains dissolved compounds. Explain one benefit of drinking hard water. [2]

Answer 9

• development of teeth / bones…

- …because it contains calcium ions / compounds

Question 10

What is the name of the solid formed when hard water reacts with soap? [2]

Answer 10

scum / calcium stearate

Question 11

Using temporary hard water in an electric kettle reduces the efficiency of the kettle. Describe how this happens. [4]

Answer 11

• temporary hard water contains calcium hydrogencarbonate
• when heated these decompose…
• …to produce a precipitate / scale…
• …which coats the kettle / heating element

Question 12

Explain how an ion exchange resin changes the dissolved compounds in tap water to improve the water. [3]

Answer 12

• an ion exchange resin contains sodium / hydrogen ions…
• …which replace the calcium / magnesium ions…
• …therefore removing the hardness

Question 13

Another student at the campsite boils some of the hard spring water in a pan. The inside of the pan becomes coated with a white solid.
Explain how the white solid is produced. [3]

Answer 13

• water contains (calcium) hydrogen carbonate…
• …which decomposes (on heating)…
• …to (calcium) carbonate