water (topic 10)

Question 1

explain how potable water can be produced from fresh water (3)

Answer 1

• river, stream, lake
• water passed through filter beds removing undissolved solids
• sterilise the water using chlorine
• destroys harmful microbes

Question 2

suggest a method you might use to obtain potable water from seawater (1)

Answer 2

distillation

Question 3

discuss one disadvantage of using distillation to obtain potable water

Answer 3

• large energy requirement to boil water
• expensive process due to energy requirement

Question 4

describe the role of filter beds in the filtration process (1)

Answer 4

• filtration removes the undissolved solids from the water

Question 5

after water has been filtered it needs to be sterilised, explain how and why the water needs to be sterilised (2)

Answer 5

• sterilised by adding chlorine
• these will kill any harmful bacteria in the water

Question 6

explain the difference between potable water and pure water (3)

Answer 6

• potable water is water that is safe to drink
• potable water may contain molecules other than H2O
• pure water only contains water molecules (H2O)

Question 7

describe how the student could remove undissolved solids from the water (2)

Answer 7

• pour water through a filter funnel
• water will pass through filter
• undissolved solids will be caught in the filter paper

Question 8

describe how the student could obtain potable water from the water obtained (3)

Answer 8

• distillation
• heat the sample until it boils
• the boiling water passes through a condenser
• and collected in a beaker

Question 9

Answer 9

Question 10

describe how the student could test the pH of the water, and what results would suggest the water is potable (2)

Answer 10

• dip a piece of litmus paper in the sample and compare to a colour chart
• pH should be between 6.5 - 8.5 to be potable

Question 11

describe the two other criteria for the water to be considered potable (2)

Answer 11

• low level of dissolved solids
• must contain no micro-organisms

Question 12

describe how the student could make water that contains bacteria safe to drink (2)

Answer 12

• sterilise the water
• add a small amount of chlorine to kill bacteria
• distill the water to remove bacteria

Question 13

suggest one use for the solid sewage removed from the waste water (2)

Answer 13

• it can be used as fertiliser
• it can be incinerated and used for energy