AQA · Chemistry · 8462
GCSE Chemistry (AQA): Potable Water
Topic 10 — Using Resources. Generated from the caption track of Cognito's lesson video "GCSE Chemistry - Potable Water - Treating Freshwater | Desalinating Seawater (2027/28 exams)"; each card deep-links to the moment in the video it came from. Lesson 10.1 of Cognito's AQA GCSE Combined Science (Trilogy) and Chemistry course (Higher tier), filed under AQA Chemistry 8462. Teaching by Cognito — https://cognitoedu.org/coursesubtopic/c2-gcse-aqa-h-c_10.1.
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What is desalination?
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A technique for extracting potable water from seawater, used where fresh water supplies are poor.
Why is desalination impractical for producing large quantities of water?
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Both distillation and reverse osmosis require huge amounts of energy, making them very expensive.
Why is groundwater preferred over surface water in hot, sunny areas?
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Surface water is exposed to the sun and can dry up, whereas groundwater is protected underground.
What pH range must potable water fall between?
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Between 6.5 and 8.5 — so it is neither too acidic nor too alkaline.
What does the bed of sand and gravel do in water treatment?
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It filters out the smaller solid particles left after the wire mesh.
What is fresh water?
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Water that has very little dissolved in it, such as rainwater collected as surface water or groundwater.
How does reverse osmosis desalinate seawater?
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The salty water is passed through a membrane that only lets water molecules through, trapping the ions and larger molecules.
Potable water must contain no ?, such as bacteria or fungi.
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microorganisms
Name three ways of sterilising water during treatment.
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Bubbling chlorine gas through it, exposing it to ozone, or exposing it to ultraviolet light.
What is the first step in treating fresh water to make it potable?
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Passing it through a wire mesh to filter out large objects such as twigs.
Why is potable water not classed as pure water in chemistry?
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Pure water contains only H₂O molecules, but potable water contains other dissolved substances.
What is an aquifer?
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An area of permeable rock under the ground that traps water — a groundwater source.
Name two examples of surface water sources.
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Lakes and rivers (reservoirs also count) — bodies of water exposed at their surface.
What is potable water?
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Water that is safe to drink. It is not the same as pure water, since it still contains dissolved substances.
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