AQA · A-Level · Chemistry
Course version: 7405 · Version from Sept 2016
Appreciate that society assesses the advantages and disadvantages when…
Full specification wording
Uses of chlorine and chlorate(I): Appreciate that society assesses the advantages and disadvantages when deciding if chemicals should be added to water supplies.
Adding anything to a public water supply is a judgement about risk against benefit, and it is not one that chemistry can settle alone.
Checked against the AQA 7405 specification (opens in a new tab) on .
- Point 3 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Adding anything to a public water supply is a judgement about risk against benefit, and it is not one that chemistry can settle alone. Chlorine prevents cholera and typhoid, diseases that killed on a huge scale before treatment; against that, chlorine is toxic and can react with organic matter in the water to form trace chlorinated compounds suspected of being carcinogenic. Fluoride reduces tooth decay; against that are dental fluorosis at higher doses and the objection that nobody can opt out of what comes from their tap. The decisive point in both cases is dose: a substance harmful in quantity may be entirely safe and useful at a few parts per million. Weighing that, and deciding who consents, is a question for society, informed by chemists rather than settled by them.
What earns the marks
- A named benefit together with the harm it prevents, such as chlorine killing the bacteria that cause cholera.
- A named risk, such as chlorine being toxic or forming chlorinated organic compounds.
- Referring to the fact that individuals cannot choose whether to receive treated water.
- A reasoned judgement that weighs the two sides rather than listing them.
Common mistakes and how to put them right
Writing that chlorine is bad for you with no named effect or concentration.
Ignoring that risk depends on dose, so a controlled amount can be safe.
Giving only scientific arguments when the question is about how society decides.
Confusing chlorination with fluoridation and giving the wrong purpose for each.
Exam tips
- These questions are marked for balance, so give at least one point on each side plus a conclusion.
- Use the word dose or concentration; it is usually the pivot on which the argument turns.
Try the lesson
The start of the Uses of chlorine and chlorate(I): Appreciate that society assesses the advantages and disadvantages when deciding if chemicals should be added to water supplies. lesson, made from checked teaching notes for this specification point.
Have a go first
When a water company proposes adding a chemical to a public water supply, which approach best describes how society reaches a decision?
Listen
Adding anything to a public water supply is a judgement about risk against benefit, and it is not one that chemistry can settle alone. Chlorine prevents cholera and typhoid, diseases that killed on a huge scale before treatment; against that, chlorine is toxic and can react with organic matter in the water to form trace chlorinated compounds suspected of being carcinogenic. Fluoride reduces tooth decay; against that are dental fluorosis at higher doses and the objection that nobody can opt out of what comes from their tap. The decisive point in both cases is dose: a substance harmful in quantity may be entirely safe and useful at a few parts per million. Weighing that, and deciding who consents, is a question for society, informed by chemists rather than settled by them. A strong answer earns marks for these points. a named benefit together with the harm it prevents, such as chlorine killing the bacteria that cause cholera. a named risk, such as chlorine being toxic or forming chlorinated organic compounds. referring to the fact that individuals cannot choose whether to receive treated water. a reasoned judgement that weighs the two sides rather than listing them. Exam tip: These questions are marked for balance, so give at least one point on each side plus a conclusion.
Key words
Say what each word means before you turn the card.
risk and benefit
Try answering aloud or in your head before turning the card.
chlorination
Try answering aloud or in your head before turning the card.
fluoridation
Try answering aloud or in your head before turning the card.
importance of dose
Try answering aloud or in your head before turning the card.
See every definition
- risk and benefit
- Society assesses the advantages and disadvantages when deciding if chemicals should be added to water supplies.
- chlorination
- Chlorine prevents cholera and typhoid, but chlorine is toxic and can react with organic matter to form trace chlorinated compounds suspected of being carcinogenic.
- fluoridation
- Fluoride reduces tooth decay, but at higher doses there is dental fluorosis and the objection that nobody can opt out of what comes from their tap.
- importance of dose
- A substance harmful in quantity may be entirely safe and useful at a few parts per million, so risk depends on dose.
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