Chemical Tests: Answers
Describe the test for oxygen gas.
Take a glowing splint and place it into the test tube containing the gas. The splint will relight if oxygen is present.
Describe the test used to detect chloride, bromide and iodide ions in solution. What is the purpose of adding dilute nitric acid?
Add dilute nitric acid followed by silver nitrate. The dilute nitric acid removes any sulfate or carbonate ions. If chloride ions are present, a white precipitate of silver chloride will be seen. Bromide ions produce a cream precipitate of silver bromide and iodide ions produce a pale yellow precipitate of silver iodide.
Describe the test for calcium.
Clean a nichrome or platinum wire by placing it in acid then into the Bunsen flame. Place it into the sample of metal then place it back into the Bunsen flame. It is important that it is a non-luminous flame so that we can clearly see the colour change. If calcium is present, we will see an orange-red flame.
How can I use a chemical test to determine whether I have Fe2+ or Fe3+ ions in solution?
Add an alkali, such as sodium hydroxide (NaOH) to the solution. If you have Fe2+ ions then a green precipitate will be formed. For Fe3+ ions, a brown precipitate will be seen.
Describe a chemical test and a physical test for water.
A chemical test involves adding anhydrous copper sulfate, which turns blue when added to water (forming hydrated copper sulfate). A physical test for water involves heating it to exactly 100oC to see if it boils. If the water is impure, the boiling point will vary from 100oC.