Learning focus
Develop safe and reproducible practical methods, record precise observations and measurements, process evidence and evaluate experimental quality.
Chlorine
Chlorine bleaches damp litmus paper. It may first show acidic behaviour, but the required observation is bleaching. Use only small quantities with ventilation.
Hydrogen and oxygen
Hydrogen gives a squeaky pop with a lighted splint. Oxygen relights a glowing splint. The splint condition must be stated correctly.
Sulfur dioxide
Sulfur dioxide changes acidified aqueous potassium manganate(VII) from purple to colourless because it acts as a reducing agent.
Avoiding confusion
Carbon dioxide extinguishes a flame but extinguishing alone is not the prescribed confirmation. Use limewater. Likewise, “pops” identifies hydrogen only when a lighted splint is used.
Practical or data skill
Prepare a six-gas test table from memory, then check it against the official notes.
Examination tip
Write the exact test and exact positive result, including “glowing” or “lighted”.
Review questions and suggested answers
Question 1
Which gas relights a glowing splint?
Suggested answer
Oxygen.
Question 2
Which gas pops with a lighted splint?
Suggested answer
Hydrogen.
Question 3
What does sulfur dioxide do to acidified manganate(VII)?
Suggested answer
Changes it from purple to colourless.
