Chemistry - Water test

Question 1

what is a solute?

Answer 1

the substance that is being dissolved (can be solid, liquid or gas)

Question 2

what is a solvent?

Answer 2

the liquid that is doing the dissolving (most commonly water)

Question 3

what is a solution?

Answer 3

a mixture of a solute in a solution

Question 4

which ions does water contain?

Answer 4

calcium, magnesium, sodium, chloride and sulfate

Question 5

how can pollutants enter the water?

Answer 5

chemical fertilisers and pesticides from farmland/animal waste can be washed into rivers and lakes by rainfall

Question 6

what is desalination? How can we desalinate water?

Answer 6

the process of removing salt from seawater through reverse osmosis or a similar method to distillation.

Question 7

how many reservoirs are in the UK?

Answer 7

around 2000

Question 8

why is treating water expensive?

Answer 8

water treatments plants have to be built. there are also environmental implications.

Question 9

list 3 advantages of adding fluoride to the water supply

Answer 9

• it alters the structure of developing enamel of young children so it is resistant to erosion by acid.
• low levels of fluoride increase the rate of remineralisation
• it reduces the ability of plaque bacteria to form acid.

Question 10

list 3 disadvantages of adding fluoride to the water supply

Answer 10

• dental fluorosis can occur if teeth are exposed to high levels of fluoride (doesn’t damage teeth or health)
• fluoride is already in 90% of toothpaste so may be deemed unnecessary
• some think drinking water should be natural with no artificial additions. chlorine is added as a safety measure only.

Question 11

describe the process of sedimentation (1)

why is it important?

Answer 11

water is stored in a large tank/reservoir, slowing down the water flow. the cleaner water is then extracted for the next stage.

this allows large insoluble particles to settle to the bottom

Question 12

describe the process of filtration (2)

why is it important?

Answer 12

the water is sprayed onto specifically prepared layers of sand and gravel.

as it trickles through, smaller insoluble particles are removed.

Question 13

describe the process of chlorination (3)

why is it important?

Answer 13

a very small amount of chlorine gas is injected into the water

this sterilises it. it is poisonous and so kills microorganisms

Question 14

what is distillation?

Answer 14

the process during which a liquid is heated to boiling point in order to vapourize it, then condensed back into a liquid so that it is separated from impurities or other solutes.

Question 15

what is the difference between hard water and soft water?

Answer 15

Hard water is water with excess calcium and magnesium, while soft water is free from these ions.

Question 16

“when temporary hard water is boiled, the hardness is removed; the hydrogencarbonate ions break down when heated”

write the word and symbol equations for this sentence

Answer 16

calcium hydrogen carbonate –> calcium carbonate +water +carbon dioxide

Ca(HC0₃)₂ —> CaC0₃ + H₂0 + CO₂