Question 1 Medium
In sewage treatment, which stage lets solids settle to make sludge and effluent?
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Answer: sedimentation
- Solids sink to the bottom.
- This stage is sedimentation.
Earth's resources, potable water and waste water: GCSE Combined Science Chemistry practice questions
A second set of questions on Earth's resources, potable water and waste water. They are different from the ones on the topic page. Try each, then open the answer and compare your working.
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Question 2 Medium
Anaerobic digestion of sewage sludge happens without which gas?
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Answer: oxygen
- Anaerobic means without oxygen.
- So the gas is oxygen.
Question 3 Hard
A 50 cm³ sample of water leaves 0.040 g of solid when evaporated. Calculate the dissolved solids in g/dm³.
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Answer: 0.80 g/dm³
- 50 cm³ = 0.050 dm³.
- 0.040 ÷ 0.050 = 0.80 g/dm³.
Question 4 Hard
A 250 cm³ sample leaves 0.30 g of solid when evaporated. Calculate the dissolved solids in g/dm³.
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Answer: 1.2 g/dm³
- 250 cm³ = 0.250 dm³.
- 0.30 ÷ 0.250 = 1.2 g/dm³.
Question 5 Hard
What does tap water contain that distilled water does not?
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Answer: dissolved salts
- Distilled water is pure.
- Tap water has dissolved salts.
Question 6 Hard
Which stage of sewage treatment uses bacteria and air to treat the liquid effluent?
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Answer: aerobic biological treatment
- The effluent is treated with air.
- Aerobic bacteria break down the organic matter.
Question 7 Hard
What does the filter bed remove from water?
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Answer: solid particles
- Sand and gravel catch what cannot pass through.
- They remove solid particles.
Question 8 Hard
Which is easiest to turn into potable water: ground water, waste water or sea water?
Show answer
Answer: ground water
- Ground water is fresh.
- It has low levels of dissolved salts.
Quick checks
Short questions with options. Choose one before you open the answer.
Check 1
What is a finite resource?
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A resource that will run out because it cannot be replaced as fast as we use it.
Check 2
What is a renewable resource?
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A resource that can be replaced as fast as we use it, such as wood from replanted forests.
Check 3
What is sustainable development?
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Meeting the needs of people today without stopping future generations meeting their needs.
Check 4
What is potable water?
Show answer
Water that is safe to drink.
Check 5
Is potable water pure?
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No. It contains dissolved substances, so it is a mixture.
Check 6
What is pure water in chemistry?
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Only H₂O, with nothing else dissolved in it.
Check 7
Name the three stages for making potable water from fresh water.
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Filtering (with sedimentation), then sterilising.
Check 8
What is the purpose of filter beds?
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To remove solid particles from the water.
Check 9
Name three sterilising agents for water.
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Chlorine, ozone and ultraviolet light.
Check 10
Why is water sterilised?
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To kill harmful bacteria and viruses.
Check 11
What is desalination?
Show answer
Removing salt from sea water.
Check 12
Name two ways to desalinate sea water.
Show answer
Distillation and reverse osmosis.
Check 13
Why are desalination methods expensive?
Show answer
They need large amounts of energy.
Check 14
How does distillation purify sea water?
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The water is boiled, the steam is condensed and collected, and the salts are left behind.
Check 15
What does the membrane do in reverse osmosis?
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It lets water through but not the dissolved salts.
Check 16
What are the four stages of sewage treatment?
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Screening and grit removal, sedimentation, anaerobic digestion of sludge, aerobic treatment of effluent.
Check 17
What is sewage sludge?
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The solid that settles out in the sedimentation stage.
Check 18
What is effluent?
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The liquid left after the sludge has settled.
Check 19
What does anaerobic mean?
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Without oxygen.
Check 20
What does aerobic mean?
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With oxygen (air).
Check 21
Why is distilled water used in chemical analysis?
Show answer
It has no dissolved salts that could affect the results.
Check 22
How can you find the dissolved solids in a water sample?
Show answer
Evaporate a known volume and weigh the solid left.
Check 23
Which water is easiest to make potable: fresh, waste or salty?
Show answer
Fresh (ground) water is easiest. Waste water and sea water need much more treatment.
Check 24
Give an example of a natural product replaced by a synthetic one.
Show answer
Natural rubber replaced by synthetic rubber, or wool by polyester.
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