tests for gases and ions

Question 1

2:47 describe tests for these cations: NH₄⁺ using sodium hydroxide solution and identifying the gas evolved, and Cu²⁺, Fe²⁺ and Fe³⁺ using sodium hydroxide solution

Answer 1

NH₄⁺:
- add sodium hydroxide and warm
- if ammonium ions are present, ammonia gas will form
- ammonia gas turns damp red litmus paper blue

Cu²⁺:
- add sodium hydroxide
- blue precipitate (copper hydroxide) forms

Fe²:
- add sodium hydroxide
- green precipitate of iron (ii) forms

Fe³⁺:
- add sodium hydroxide
- brown precipitate of iron (iii) forms

Question 2

2:48 describe tests for these anions: Cl⁻, Br⁻ and I⁻ using acidified silver nitrate solution, SO₄²⁻ using acidified barium chloride solution, CO₃²⁻ using hydrochloric acid and identifying the gas evolved

Answer 2

halide ions test:
- add nitric acid to remove impurities (like carbonate ions)
- then add silver nitrate solution

chloride:
- white precipitate
- of silver chloride

bromide:
- cream precipitate
- of silver bromide

iodide:
- yellow precipitate
- of silver iodide

sulfate ions test:
- add hydrochloric acid to remove impurities (like carbonate ions)
- then add barium chloride solution
- if sulfate ions are present, a white precipitate of barium sulfate forms

carbonate ions test:
- add hydrochloric acid
- if carbonate ions are present, fizzing will occur
- carbon dioxide is a product, can be tested with limewater

Question 3

2:49 describe a test for the presence of water using anhydrous copper(II) sulfate

Answer 3

• add anhydrous copper (II) sulfate (CuSO4) to a sample
• if water is present the anhydrous copper (II) sulfate will change from white to blue