AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Halide ions in solution produce precipitates with silver nitrate solution…
Full specification wording
Halides: Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid.
Halide ions in aqueous solution can be identified by adding dilute nitric acid followed by silver nitrate solution.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 1 of 2
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Halide ions in aqueous solution can be identified by adding dilute nitric acid followed by silver nitrate solution. The nitric acid removes carbonate ions that would otherwise form a white precipitate with silver nitrate and confuse the result. Silver ions then combine with halide ions to form insoluble silver halides: Ag⁺(aq) + Cl⁻(aq) → AgCl(s), and similarly for bromide and iodide. The precipitate colour identifies the halide: chloride gives white, bromide gives cream and iodide gives yellow. The test works because silver halides are insoluble in water and form a solid suspension.
What earns the marks
- State that dilute nitric acid is added before silver nitrate solution when testing for halide ions.
- Explain that nitric acid reacts with carbonate ions to prevent a false white precipitate of silver carbonate.
- Describe the formation of a precipitate when silver nitrate solution is added to a solution containing halide ions.
- Write the ionic equation Ag⁺(aq) + Cl⁻(aq) → AgCl(s) for chloride, and equivalent equations for bromide and iodide.
- Relate the colour of the precipitate to the halide present: white for chloride, cream for bromide and yellow for iodide.
- Recognise that the test identifies halide ions in solution rather than the element or molecule.
Common mistakes and how to put them right
Adding silver nitrate before nitric acid.
Put it right: Add dilute nitric acid first to remove carbonate ions.
Using hydrochloric acid instead of nitric acid.
Put it right: Hydrochloric acid would introduce chloride ions and give a false positive.
Writing that the precipitate is silver halide molecules rather than an ionic solid.
Put it right: Describe the precipitate as an insoluble ionic compound.
Exam tips
- State the order of addition clearly: dilute nitric acid first, then silver nitrate solution.
- Give the colour and the halide together, for example chloride gives a white precipitate.
- Use state symbols in ionic equations to show that the silver halide is solid.
Try the lesson
The start of the Halides: Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid. lesson, made from checked teaching notes for this specification point.
Have a go first
Which reagent is added to a solution containing halide ions to produce a precipitate?
Listen
Halide ions in aqueous solution can be identified by adding dilute nitric acid followed by silver nitrate solution. The nitric acid removes carbonate ions that would otherwise form a white precipitate with silver nitrate and confuse the result. Silver ions then combine with halide ions to form insoluble silver halides: Ag⁺(aq) + Cl⁻(aq) → AgCl(s), and similarly for bromide and iodide. The precipitate colour identifies the halide: chloride gives white, bromide gives cream and iodide gives yellow. The test works because silver halides are insoluble in water and form a solid suspension. A strong answer earns marks for these points. State that dilute nitric acid is added before silver nitrate solution when testing for halide ions. Explain that nitric acid reacts with carbonate ions to prevent a false white precipitate of silver carbonate. Describe the formation of a precipitate when silver nitrate solution is added to a solution containing halide ions. Write the ionic equation Ag⁺(aq) + Cl⁻(aq) → AgCl(s) for chloride, and equivalent equations for bromide and iodide. A common slip: Adding silver nitrate before nitric acid. Instead, add dilute nitric acid first to remove carbonate ions. Exam tip: State the order of addition clearly: dilute nitric acid first, then silver nitrate solution.
See it
Key words
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Halide identification
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Precipitation reactions
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Ionic equations
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Reagent order and control
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See every definition
- Halide identification
- Halide ions in aqueous solution can be identified by adding dilute nitric acid followed by silver nitrate solution, and the precipitate colour identifies the halide.
- Precipitation reactions
- Silver ions combine with halide ions to form insoluble silver halides, which form a solid suspension.
- Ionic equations
- The ionic equation for chloride is Ag⁺(aq) + Cl⁻(aq) → AgCl(s), and equivalent equations are written for bromide and iodide.
- Reagent order and control
- Dilute nitric acid is added before silver nitrate solution, because the nitric acid removes carbonate ions that would otherwise form a white precipitate and confuse the result.
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