C3.2 Water

Question 1

How is hard water produced from rain water?

Answer 1

calcium/magnesium ions dissolve
from rocks (limestone)

Question 2

What is formed when hard water reacts with soap

Answer 2

scum

Question 3

State one health benefit of drinking hard water

Answer 3

• helps maintain bones
• helps maintain teeth
• helps reduce heart disease

Question 4

Why is distillation generally not used to purify water

Answer 4

High cost of energy

Question 5

Why is chlorine added to water

Answer 5

• kill microbes

- sterilise it

Question 6

What in water filters reduce the hardness of water

Answer 6

Ion exchange column

Question 7

Suggest why water filters contain particles of nanosilver

Answer 7

• kill microbes

- sterilise it

Question 8

Describe the main two steps used to treat water from reservoirs

Answer 8

• filter
• to remove solids
• add chlorine
• to kill bacteria/sterilise it

Question 9

A student boils some hard spring water in a pan.
The inside of the pan becomes coated with a white solid.
Explain how the white solid is produced.

Answer 9

• water contains calcium hydrogen carbonate (HCO₃^-)
• which decomposes
• to form calcium carbonate (or limescale)

Question 10

Explain how an ion exchange column softens water

Answer 10

• Sodium ions (Na⁺) in <u>the resin</u>
• replace
• calcium ions(Ca²⁺)/magnesium ions (Mg²⁺)

Question 11

Why do some companies add fluoride to the drinking water?

Answer 11

-Improve dental health (reduce tooth decay)

Question 12

Describe how sodium carbonate is used to soften water

Answer 12

• sodium carbonate is added to hard water
• calcium ions precipitate out (form a solid)
• as calcium carbonate
• which can be filtered out of the water

Question 13

How is scale formed?

Answer 13

• temporary soft water is heated
• hydrogen carbonate ions decompose
• to form carbonates

Question 14

People who use hard water can expect higher costs than people who use soft water.
Explain why.

Answer 14

either
Forms scum
more soap is needed to form a lather

or

forms scale on heating
making kettles/heating systems less efficient