Carbonates, Halides & Sulfates
Science Practicals: GCSE, topic 2.1.12
Reactions of Carbonates
When carbonates react with dilute acids, the following products are formed:
A salt
Carbon dioxide
Water
Testing for Halides
Halide ions are negatively charged (they are anions). There are 2 steps to halide testing:
Add dilute nitric acid
- 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 step 2.
Add silver nitrate
- Add silver nitrate to the same solution.
- If halide ions are present, they will form a precipitate with the silver ions:
- 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).
Testing for Sulfates
Sulfates are compounds that contain SO42- ions. There are 2 steps to sulfate testing:
Add dilute hydrochloric acid
- Add dilute hydrochloric acid to an unknown solution.
- This removes carbonate ions. These could disrupt test results by forming a precipitate with the barium ions added in step 2.
Add barium chloride
- Add barium chloride to the same solution.
- If sulfates are present, the white precipitate barium sulfate will form:
- Ba2+(aq) + SO42-(aq) → BaSO4(s)
Test yourself on Carbonates, Halides & Sulfates
How could you confirm that carbonates produce carbon dioxide when they react with dilute acids?
Why is dilute nitric acid added to a solution before it is tested for halide ions?
What ions do carbonates contain?
What colour are the following halide precipitates?
Which of the following are involved in testing for halides?