Water

Question 1

What are the hard water ions?

Answer 1

Calcium an magnesium

Question 2

How do hard water ions get into water?

Answer 2

When water runs over rocks like limestone or gypsum, compounds like magnesium sulphate and calcium sulphate dissolve into the water.

Question 3

What happens when you mix soft water with soap?

Answer 3

You get a nice lather.

Question 4

What happens when hard water is mixed with soap? Why?

Answer 4

Scum is formed because the calcium and magnesium ions react with the soap to form insoluble scum. Therefore you need more hard water to get a decent lather which wastes money.

Question 5

What are two benefits of hard water?

Answer 5

• Calcium aids the development and maintenance of healthy teeth and bones
• Links have been made between drinking hard water and reduced chances of heart disease

Question 6

What are the two types of hard water? What’s the difference?

Answer 6

Temporary and permanent hard water. When permanent hard water is boiled it remains hard.

Question 7

What happens when temporary hard water is heated?

Answer 7

It forms a calcium carbonate scale and becomes soft.

Question 8

What ion does temporary hard water contain?

Answer 8

Hydrocarbonate ions (HCO3-)

Question 9

Describe the reaction that takes place when temporary hard water is heated.

Answer 9

The hydrocarbonate ions decompose to produce carbonate ions that then react with the calcium and magnesium ions to form insoluble precipitates - scale.

Question 10

What are two disadvantages of scale?

Answer 10

• It can block pipes

* Thermal insulator so can decrease the efficiency of some appliances e.g. kettles

Question 11

What are two ways of softening permanent hard water?

Answer 11

• Adding sodium carbonate to make insoluble calcium carbonate or magnesium carbonate
• An ion exchange column

Question 12

What is an ion exchange column?

Answer 12

A column filled with sodium or hydrogen ions in insoluble resins. They are exchanged with calcium or magnesium ions when water runs through the column.

Question 13

What is the method for using titration to assess water hardness?

Answer 13

1( Fill a burette with 50 cubic centimetres of soap solution

2) Add 50 cubic centimetres of the first water sample into a flask
3) Use the burette to add 1 cubic centimetre of soap solution to the flask at a time before sealing the flask and shaking it.
4) Repeat until a lather is formed that covers the top of the water and stays for at least 30 seconds
5) Record how much soap solution was used
6) Repeat with each water sample
5) Repeat the entire experiment with boiled samples

Question 14

Where does most of our drinking water come from?

Answer 14

Reservoirs

Question 15

Where does the water in reservoirs come from?

Answer 15

Groundwater and rivers

Question 16

What four steps does water in a reservoir go through to make it safe to drink?

Answer 16

1) The water passes through a mesh screen to remove large foreign bodies
2) Chemicals are added to make microbes stick together and fall to the bottom of the tank
3) Water is filtered through gravel to catch smaller foreign bodies
4) Chlorine is added to kill off any remaining microbes

Question 17

Why do some people run their tap water through a carbon filter?

Answer 17

To remove the chlorine taste

Question 18

Why do some people run their tap water through silver filters?

Answer 18

It’s Mrs t to kill bacteria and algae.

Question 19

What are two advantages of fluoridation and chlorination?

Answer 19

• Reduces tooth decay

* Kills microbes and diseases

Question 20

What are two disadvantages of fluoridation and chlorination?

Answer 20

• Both have been linked to cancer and bone disease
• Some people object to mass medication and say that people should choose whether they want fluoridation and chlorination or not

Question 21

How does one make pure water?

Answer 21

Heat water to make steam and then condense the steam back into water. The ions in the water don’t evaporate making the condensed water totally pure.

Question 22

What is a disadvantage of distilled pure water?

Answer 22

It requires a lot of energy so is expensive.

Question 23

Where is distilled pure water used?

Answer 23

Chemistry labs