Testing for Carbonate and Halides
Chemistry: Edexcel IGCSE, topic 13.2.8
Testing for Carbonate and Halides
There is a specific way to test for the presence of carbonates and halides.
Testing for carbonates
- Carbonates are compounds containing CO32− ions.
- Carbonates react with dilute acids to form a salt, carbon dioxide, and water.
- E.g. calcium carbonate + hydrochloric acid → calcium chloride + carbon dioxide + water
Testing for carbonates cont.
- As carbon dioxide is produced, we can use the standard carbon dioxide test to work out if an unknown substance is a carbonate.
- This test involves bubbling the gas through limewater. If the solution turns cloudy, the gas is carbon dioxide and the compound is a carbonate.
Testing for halides
- Halides are compounds containing ions of halogen atoms.
- There are two steps to halide testing:
- Add dilute nitric acid to an unknown solution.
- This removes carbonate ions. These could disrupt test results by forming a precipitate with the silver ions added in the second step.
- Add silver nitrate to the same solution.
- If halide ions are present, they will form a precipitate with the silver ions.
Testing for halides cont.
- Ag+(aq) + Cl-(aq) → AgCl(s)
- Silver chloride is white.
- Ag+(aq) + Br-(aq) → AgBr(s)
- Silver bromide is cream.
- Ag+(aq) + I-(aq) → AgI(s)
- Silver iodide is pale yellow.
Test yourself on Testing for Carbonate and Halides
What is produced when testing calcium iodide solution with dilute nitric acid followed by silver nitrate?
Upon testing for the presence of certain ions by adding silver nitrate to a solution, Michaela notices that a precipitate forms. What can she deduce about the solution?