AQA · A-Level · Chemistry
Course version: 7405 · Version from Sept 2016
The use of acidified silver nitrate solution to identify and distinguish…
Full specification wording
Trends in properties: The use of acidified silver nitrate solution to identify and distinguish between halide ions.
Silver halides are insoluble and conveniently different in colour, which is what makes silver nitrate the standard test.
Checked against the AQA 7405 specification (opens in a new tab) on .
- Point 5 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Silver halides are insoluble and conveniently different in colour, which is what makes silver nitrate the standard test. Add dilute nitric acid first, then silver nitrate solution. Fluoride gives no precipitate, because silver fluoride is soluble. Chloride gives a white precipitate, bromide a cream one and iodide a yellow one, each by Ag⁺(aq) + X⁻(aq) → AgX(s). The precipitates darken on standing in light as silver is formed, which is the basis of photographic film. The acid matters: carbonate, hydroxide and sulfite ions all precipitate with silver ions and would be mistaken for a halide, and the nitric acid removes them. It must be nitric acid, because hydrochloric acid would introduce chloride ions and sulfuric acid would precipitate silver sulfate.
What earns the marks
- Adding dilute nitric acid before the silver nitrate solution.
- The colours: white with chloride, cream with bromide and yellow with iodide.
- No precipitate with fluoride ions.
- The ionic equation Ag⁺(aq) + X⁻(aq) → AgX(s) with state symbols.
- Naming the complete reagent, silver nitrate solution, rather than the silver ion alone.
Common mistakes and how to put them right
Acidifying with hydrochloric acid, which adds chloride ions and gives a false white precipitate.
Acidifying with sulfuric acid, which would precipitate silver sulfate.
Swapping the colours, calling the bromide precipitate yellow and the iodide cream.
Omitting state symbols from the ionic equation when they are required.
Naming the reagent as Ag⁺ rather than silver nitrate, which examiners treat as an incomplete reagent.
Exam tips
- A reagent must be something you could take out of a bottle, so write silver nitrate solution, not silver ions.
- Learn the colours in group order, white then cream then yellow, so they cannot be swapped under pressure.
Try the lesson
The start of the Trends in properties: The use of acidified silver nitrate solution to identify and distinguish between halide ions. lesson, made from checked teaching notes for this specification point.
Have a go first
What is added to a solution to test for halide ions using silver nitrate?
Listen
Silver halides are insoluble and conveniently different in colour, which is what makes silver nitrate the standard test. Add dilute nitric acid first, then silver nitrate solution. Fluoride gives no precipitate, because silver fluoride is soluble. Chloride gives a white precipitate, bromide a cream one and iodide a yellow one, each by Ag⁺(aq) + X⁻(aq) → AgX(s). The precipitates darken on standing in light as silver is formed, which is the basis of photographic film. The acid matters: carbonate, hydroxide and sulfite ions all precipitate with silver ions and would be mistaken for a halide, and the nitric acid removes them. It must be nitric acid, because hydrochloric acid would introduce chloride ions and sulfuric acid would precipitate silver sulfate. A strong answer earns marks for these points. adding dilute nitric acid before the silver nitrate solution. the colours: white with chloride, cream with bromide and yellow with iodide. no precipitate with fluoride ions. the ionic equation Ag⁺(aq) + X⁻(aq) → AgX(s) with state symbols. Exam tip: A reagent must be something you could take out of a bottle, so write silver nitrate solution, not silver ions.
See it
Key words
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halide ion test
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silver halide colours
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acidifying with nitric acid
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ionic equations with state symbols
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See every definition
- halide ion test
- The use of acidified silver nitrate solution to identify and distinguish between halide ions.
- silver halide colours
- Chloride gives a white precipitate, bromide a cream one and iodide a yellow one, while fluoride gives no precipitate because silver fluoride is soluble.
- acidifying with nitric acid
- Dilute nitric acid is added first because carbonate, hydroxide and sulfite ions would otherwise precipitate with silver ions and be mistaken for a halide.
- ionic equations with state symbols
- Each precipitate forms by Ag⁺(aq) + X⁻(aq) → AgX(s), and the state symbols are required.
Label the diagram
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