C3 Water

Question 1

What is the difference between permanent and temporary hard water?

Answer 1

Permanent hard water stays hard when it is boiled. Temporary hard water is softened by boiling.

Question 2

How do you get rid of the microbes in water during water treatment?

Answer 2

By sterilising with chlorine.

Question 3

Why is drinking water neutralised during treatment?

Answer 3

Acids taste sour; alkalis taste soapy, neutral water has no taste.

Question 4

Why is fluoride added to drinking water?

Answer 4

Fluoride may be added to improve dental health though this is controversial.

Question 5

What are the advantages of hard water?

Answer 5

Calcium cmpds are good for the growth and maintenance of bones and teeth; they help to reduce heart disease; it makes good tea!

Question 6

Is the water that we drink pure and safe? Explain your answer.

Answer 6

The water we drink is not pure because it contains dissolved substances. It should be safe to drink treated water as it does not contain anything that could harm us.

Question 7

Suggest an area of the world that might use distillation to make water.

Answer 7

Somewhere wealthy, The Gulf States.

Question 8

Explain why distillation is an expensive way to make drinking water.

Answer 8

A large amount of energy is needed to boil the water so high costs are involved.

Question 9

What causes temporary hard water and why is it treatable?

Answer 9

It contains hydrogencarbonate ions (HCO₃^––). These decompose on heating to produce carbonate ions which react with Ca²⁺ and Mg²⁺ ions to form precipitates that remove the hardness as limescale.

Question 10

What is hard water?

Answer 10

Hard water reacts with soap to form scum and so more soap is needed to form lather.

Question 11

How do ion exchange columns soften hard water?

Answer 11

Ion exchange columns contain sodium ions, which replace the calcium and magnesium ions when hard water passes through the column.

Question 12

Some people use water filters on their tap water, what do they filter out?

Answer 12

They remove some dissolved substances from tap water to improve the taste and quality.

Question 13

What is in commercial water filters?

Answer 13

They contain activated charcoal (carbon), silver and ion exchange resins

Question 14

How does sodium carbonate soften hard water?

Answer 14

It reacts with the Ca2+ and Mg2+ ions to form a precipitate of calcium or magnesium carbonate

Question 15

Some people make drinking water using distillation, what does this mean?

Answer 15

Water, even seawater, is boiled. The steam is condensed as pure water.

Question 16

What are soapless detergents?

Answer 16

Soapless detergents do not form scum.

Question 17

How would you compare the effects of water softening by bath salts and ion exchange?

Answer 17

Take a water sample and separate it into three equal parts. Pass one through an ion exchange resin, add bath salts to the second and filter. Then compare the hardness of the three samples by titrating with soap solution.

Question 18

What is soft water?

Answer 18

Soft water readily forms lather with soap.

Question 19

How would you compare the hardness of two water samples?

Answer 19

By titrating with soap solution. i.e. add soap solution from a burette and shake the water to see if forms a lasting lather.

Question 20

Why is chlorine added to drinking water?

Answer 20

To kill/sterilise the pathogens/microbes

Question 21

How do you get rid of suspended solids in the water during treatment?

Answer 21

By passing the water through filter beds to remove any solids

Question 22

What causes hard water?

Answer 22

Hard water contains dissolved compounds, usually of calcium or magnesium, from the rocks that the water comes into contact with.

Question 23

Why do you need to put salt into a dishwasher regularly?

Answer 23

The sodium ions in the salt exchange for the calcium ions that have built up in the dishwasher’s ion exchanger.

Question 24

When choosing water to make into drinking water, where do you start?

Answer 24

By choosing an appropriate source, drinking water should have sufficiently low levels of dissolved salts and microbes; start with clean water out in the country if you can.

Question 25

What are the disadvantages of hard water?

Answer 25

Using it can increase costs because more soap is needed. When temporary hard water is heated it produces scale that coats heating elements and reduces the efficiency of heating systems and kettles.