C3.2 Water

Question 1

What does soft water form with soap?

Answer 1

Lather

Question 2

What does hard water form with soap?

Answer 2

Scum, so more soap is required to from lather

Question 3

Do soapless detergents produce scum?

Answer 3

No

Question 4

What are the two types of hard water?

Answer 4

Permanent hard water ad temporary hard water

Question 5

How can temporary hard water be softened?

Answer 5

By boiling it

Question 6

What happens when permanent hard water is boiled?

Answer 6

It remains hard

Question 7

What does temporary hard water contain?

Answer 7

Hydrogencarbonate ions

Question 8

What do the hydrogencarbonate ions in temporary hard water decompose on heating to form?

Answer 8

Calcium carbonate, this solid is ‘limescale’ on your kettle

Question 9

What do the carbonate ions produced by the hydrogencarbonate ions decomposing react with and what do they form?

Answer 9

Calcium and Magnesium ions to form precipitates

Question 10

Why can using hard water increase costs?

Answer 10

More soap is needed

Question 11

Why can heating temporary hard water reduce efficiency?

Answer 11

It produces scale that reduces the efficiency of heating systems and kettles

Question 12

What benefits does hard water have?

Answer 12

Calcium compounds are good for the development and maintenance of bones and teeth, they also help to reduce heart disease

Question 13

How can hard water be made soft?

Answer 13

By removing the dissolved calcium and magnesium ions

Question 14

How can sodium carbonate be used to make hard water soft?

Answer 14

Sodium carbonate reacts with the calcium and magnesium ions to form a precipitate of calcium carbonate and magnesium carbonate

Question 15

How do commercial water softeners make hard water soft?

Answer 15

Ion exchange columns contain hydrogen ions or sodium ions, these ions replace calcium and magnesium ions when hard water passes through the column

Question 16

What should drinking water have?

Answer 16

Low levels of dissolved salt and microbes

Question 17

How is water cleaned / purified?

Answer 17

It passes through a mesh screen to remove big bits like twigs. Chemicals are then added which make solids and microbes stick together and fall to the bottom. The water is then filtered through beds to remove all the solids. Water is then chlorinated to kill any harmful microbes left

Question 18

Water needs to come from an…

Answer 18

Appropriate source

Question 19

What do water filters contain?

Answer 19

Carbon, silver and ion exchange resins which can remove some dissolved substances from tap water to improve taste and quality

Question 20

Why may fluorine be added to drinking water?

Answer 20

To improve dental health

Question 21

Why may chlorine be added to drinking water?

Answer 21

To reduce microbes and therefore diseases

Question 22

How can pure water be produced?

Answer 22

By distillation

Question 23

What are the arguments against adding fluorine to water?

Answer 23

It can cause cancer and bone problems in high doses, some believe if they want fluorine they can use fluoride toothpaste

Question 24

Why is distillation expensive?

Answer 24

It requires a lot of energy

Question 25

What are the arguments against adding chlorine to water?

Answer 25

It can increase certain cancers, it can react with other natural substances in the water to produce toxic-by products which could also cause cancer