C3.2

Question 1

What does water we drink contain?

Answer 1

Dissolved substances, usually calcium and magnesium

Question 2

Why does water contain dissolved substances?

Answer 2

~ Water comes into contact with rocks

~ Compounds from rocks dissolve in the water

Question 3

What is scum?

Answer 3

Insoluble salts

Question 4

How do you identify whether water is hard or soft?

Answer 4

~ Shake the water with a soap solution
~ Soft water forms a lather
~ Hard water forms scum

Question 5

What are disadvantages of hard water?

Answer 5

~ Increases cost as more soap is needed

~ Reduces efficiency of heating systems and kettles because temporary hard water produces scale

Question 6

What are advantages of hard water?

Answer 6

~ Helps people to develop strong teeth and bones

~ Reduces the chance of developing heart disease

Question 7

Why is silver added to water?

Answer 7

It discourages bacteria growth

Question 8

What is an advantage and disadvantage of chlorine in water?

Answer 8

+ Kills bacteria

• Disinfectant taste
• People have no choice whether to consume it or not

Question 9

What does drinking water have to have?

Answer 9

~ Low levels of dissolved salts

~ Low levels of microorganisms

Question 9

What are the steps in making water safe to drink?

Answer 9

~ Screen (which removes large objects like leaves)
~ Sedimentation (which removes clumps of dirt)
~ Filtration (which uses sand to remove remaining insoluble solids)
~ Disinfection (chlorine is added to kill bacteria)
~ Ion exchange (removes hard ions)
~ Carbon and silver added (carbon decreases chlorine, silver discourages bacteria growth)

Question 11

What does temporary hard water have?

Answer 11

HCO3 ions

Question 11

What are advantages and disadvantages of fluorine in water?

Answer 11

+ Good for teeth and bones
+ Reduces chance of heart disease
- Has links with learning difficulties
- People have no choice whether to consume it or not

Question 13

Why is carbon added to water?

Answer 13

It reduces the amount of chlorine and other chemicals e.g. traces of pesticide

Question 14

What does permanent hard water have?

Answer 14

Sulphate ions and not many hydrogencarbonate ions, and is not softened by boiling

Question 15

How is temporary hard water softened?

Answer 15

It contains hydrogencarbonate ions that decompose into carbonate ions when heated. These carbonate ions react with the magnesium/calcium ions to form precipitates of magnesium carbonate/calcium carbonate

Question 16

How is hard water (permanent or temporary) softened?

Answer 16

~ Addjng sodium carbonate solution (washing soda)

~ or passing the water through an ion-exchange column

Question 17

How is hard water softened by adding sodium carbonate solution (washing soda)?

Answer 17

The carbonate ions react with the calcium/magnesium ions to form calcium carbonate/magnesium carbonate which precipitate out of solution as they’re insoluble

Question 18

How is hard water softened by passing it through an ion exchange column?

Answer 18

~ Column has resin that contain hydrogen/sodium ions

~ As the water passes through, the calcium and magnesium ions are replaced by the hydrogen/sodium ions from the resin

Question 19

Why does the resin need to be replaced in an ion exchange column?

Answer 19

Because they will run out of hydrogen/sodium ions to exchange with the magnesium and calcium

Question 20

How can any water be distilled to produce pure water?

Answer 20

~ By boiling the water to produce steam and then condensing the steam by cooling it to produce pure liquid water
~ This process uses lots of energy so is expensive