AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Sterilising agents used for potable water include chlorine, ozone or…
Full specification wording
Potable water: Sterilising agents used for potable water include chlorine, ozone or ultraviolet light.
After insoluble solids have been removed by filter beds, potable water must be sterilised to kill microbes that could cause disease.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 7 of 12
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
After insoluble solids have been removed by filter beds, potable water must be sterilised to kill microbes that could cause disease. The sterilising agents specified are chlorine, ozone and ultraviolet light. Chlorine is added as a gas or in a solution and kills microbes by disrupting their cell processes; it also provides some residual protection as water travels through pipes. Ozone is a reactive gas that destroys microbes by oxidation. Ultraviolet light is used by passing water through a chamber where UV radiation damages the genetic material of microbes so they cannot reproduce. Each method kills microbes but does not remove dissolved substances, so sterilisation is not a purification step in the chemical sense.
What earns the marks
- Sterilising kills microbes in water so that it is safe to drink.
- Chlorine is a sterilising agent used for potable water.
- Ozone is a sterilising agent used for potable water.
- Ultraviolet light is a sterilising agent used for potable water.
- Sterilisation does not remove dissolved substances; it targets microbes.
- Sterilisation follows filtration in the treatment of potable water.
Common mistakes and how to put them right
Confusing sterilisation with filtration.
Put it right: Sterilisation kills microbes while filtration removes insoluble solids.
Stating that chlorine removes dissolved salts.
Put it right: Chlorine kills microbes and does not remove dissolved substances.
Naming only one sterilising agent when asked for examples.
Put it right: Include chlorine, ozone and ultraviolet light.
Exam tips
- Learn all three sterilising agents as a set: chlorine, ozone and ultraviolet light.
- If asked why sterilisation is needed, refer to killing microbes that could cause disease.
- Avoid saying sterilisation makes water pure; it makes water safe by killing microbes.
Try the lesson
The start of the Potable water: Sterilising agents used for potable water include chlorine, ozone or ultraviolet light. lesson, made from checked teaching notes for this specification point.
Have a go first
Which of these is a sterilising agent used to treat potable water?
Listen
After insoluble solids have been removed by filter beds, potable water must be sterilised to kill microbes that could cause disease. The sterilising agents specified are chlorine, ozone and ultraviolet light. Chlorine is added as a gas or in a solution and kills microbes by disrupting their cell processes; it also provides some residual protection as water travels through pipes. Ozone is a reactive gas that destroys microbes by oxidation. Ultraviolet light is used by passing water through a chamber where UV radiation damages the genetic material of microbes so they cannot reproduce. Each method kills microbes but does not remove dissolved substances, so sterilisation is not a purification step in the chemical sense. A strong answer earns marks for these points. Sterilising kills microbes in water so that it is safe to drink. Chlorine is a sterilising agent used for potable water. Ozone is a sterilising agent used for potable water. Ultraviolet light is a sterilising agent used for potable water. A common slip: Confusing sterilisation with filtration. Instead, sterilisation kills microbes while filtration removes insoluble solids. Exam tip: Learn all three sterilising agents as a set: chlorine, ozone and ultraviolet light.
See it
Key words
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Sterilising agents
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Chlorine
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Ozone
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Ultraviolet light
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See every definition
- Sterilising agents
- Chlorine, ozone or ultraviolet light are used for potable water to kill microbes that could cause disease.
- Chlorine
- Added as a gas or in a solution, it kills microbes by disrupting their cell processes and provides some residual protection as water travels through pipes.
- Ozone
- A reactive gas that destroys microbes by oxidation.
- Ultraviolet light
- Used by passing water through a chamber where UV radiation damages the genetic material of microbes so they cannot reproduce.
Label the diagram
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1Box 1
2Box 2
3Box 3
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