Tests for gases · Grade 11
In Grade 11 you get fluent with: tests for hydrogen, oxygen and carbon dioxide; tests for chlorine and ammonia.
Each common gas has its own simple test. Hydrogen burns with a squeaky pop, oxygen relights a glowing splint, carbon dioxide turns limewater milky, chlorine bleaches damp litmus paper and ammonia turns damp red litmus paper blue. A good test gives a result that only that gas gives.
Key facts
- Gases: hydrogen burns with a squeaky pop; oxygen relights a glowing splint; carbon dioxide turns limewater milky; chlorine bleaches damp litmus paper.
- Ammonia turns damp red litmus paper blue.
- A test must be specific: many gases put out a lit splint, but only carbon dioxide turns limewater milky.
Worked examples
Example 1
A gas is collected and tested: a lighted splint burns with a squeaky pop. Which gas is it?
Answer: hydrogen
Example 2
A gas is collected and tested: it relights a glowing splint. Which gas is it?
Answer: oxygen
Example 3
Describe the tests for hydrogen, oxygen and carbon dioxide, and give the result of each.
Answer: hydrogen: a lit splint gives a squeaky pop; oxygen: it relights a glowing splint; carbon dioxide: it turns limewater milky
Example 4
How do you test for chlorine, and what is the result?
Answer: hold damp blue litmus paper in the gas: it turns red and then white (it is bleached)
Example 5
A gas from a reaction relights a glowing splint. Which gas is it? Name a reaction that could have made it.
Answer: oxygen; for example, hydrogen peroxide breaking down with manganese(IV) oxide as a catalyst
Example 6
Why is limewater used to test for carbon dioxide, rather than seeing whether the gas puts out a lit splint?
Answer: many gases, such as nitrogen, put out a lit splint, so that does not identify carbon dioxide; only carbon dioxide turns limewater milky
Example 7
A gas is collected and tested: it turns damp red litmus paper blue. Which gas is it?
Answer: ammonia