Testing for ions and gases
- Created by: emews
- Created on: 29-11-17 17:56
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- Testing for ions and gases
- It is possible to use a flame test to detect the presence of an alkali metal ion.
- The compound is put through a blue Bunsen flame. The colour produced indicates which alkali metal ion is present in the compound.
- Ammonium ions can be identified in a solution by adding dilute sodium hydroxide solution and gently heating.
- If ammonium ions are present, they will be converted to ammonia gas.
- It also turns damp red litmus paper or damp universal indicator paper blue.
- It also turns damp red litmus paper or damp universal indicator paper blue.
- It also turns damp red litmus paper or damp universal indicator paper blue.
- If ammonium ions are present, they will be converted to ammonia gas.
- To tell whether an unknown substance contains iron(II) nitrate or iron(III) nitrate, add a few drops of sodium hydroxide solution:
- if you get a green precipitate, the unknown substance is iron(II) nitrate
- if you get an orange-brown precipitate, the unknown substance is iron(III) nitrate
- Note that it is the metal that determines the colour.
- An acid, such as dilute hydrochloric acid, is added to the test compound for carbonate ions.
- Carbon dioxide gas bubbles if carbonate ions are present.
- Halide ions in solutions are detected using silver nitrate solutions.
- The test solution is acidified using a few drops of dilute nitric acid, and then a few drops of silver nitrate solution are added.
- Different coloured silver halide precipitates form, depending on the halide ions present:
- chloride ions give a white precipitate of silver chloride
- bromide ions give a cream precipitate of silver bromide
- iodide ions give a yellow precipitate of silver iodide
- Hydrogen, oxygen, carbon dioxide, ammonia and chlorine can be identified using different tests.
- A lighted wooden splint makes a popping sound in a test tube of hydrogen.
- A glowing wooden splint relights in a test tube of oxygen.
- Carbon dioxide turns limewater milky.
- It makes damp red litmus paper turn blue.
- It also makes damp blue litmus paper turn red, and then bleaches it white.
- It is possible to use a flame test to detect the presence of an alkali metal ion.
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