WAEC Chemistry 2021 Theory — Question 14
Question 14 of 31 from the West African Examinations Council (WAEC) Chemistry 2021 Theory paper, with the correct answer and a full explanation.
Advertisement
2(c). What are hydrocarbons? (i) State two natural sources of hydrocarbons. (ii) A hydrocarbon contains 83% carbon and 17% hydrogen by mass. Calculate its empirical formula. [H=1.0, C=12.0]
Model answer
Hydrocarbons are compounds containing only carbon and hydrogen. (i) Any two: coal; petroleum/crude oil; natural gas. (ii) Moles: C = 83/12 = 6.92, H = 17/1 = 17.0. Dividing by the smaller (6.92): C = 1, H ≈ 2.46 ≈ 2.5. Multiplying through by 2: C = 2, H = 5. Empirical formula = C2H5.
Advertisement
Sign up free to unlock
- Score tracking
- Practice history
- Saved questions
- Progress dashboard
- Personalized sessions
- Weak-topic breakdown
…and/or go further with premium services and No Ads.