Propane, C₃H₈, is an alkane.
(a) Give the general formula of the alkanes. [1]
(b) Write a balanced equation for the complete combustion of propane. [2]
(c) Incomplete combustion of propane in a faulty gas heater can produce carbon monoxide. Explain why carbon monoxide is poisonous. [2]
- (a) CnH2n+2(1)
- (b) $\text{C}_3\text{H}_8 + 5\text{O}_2 \rightarrow 3\text{CO}_2 + 4\text{H}_2\text{O}$: correct formulae of all reactants and products(1)
- (b) correctly balanced (allow multiples, e.g. 2C₃H₈ + 10O₂ → 6CO₂ + 8H₂O; ignore state symbols)(1)
- (c) (carbon monoxide) combines with haemoglobin (in red blood cells) (allow binds to / attaches to haemoglobin)(1)
- (c) reduces the capacity of the blood to carry oxygen (allow so less oxygen is carried around the body; ignore 'it is toxic')(1)
- Answer: (a) CₙH₂ₙ₊₂ (b) C₃H₈ + 5O₂ → 3CO₂ + 4H₂O (c) binds to haemoglobin, so blood carries less oxygen
- Examiner tip: 'It's toxic' just repeats the question — you must mention haemoglobin and oxygen transport.