Post-UTME Chemistry 2019 Objective — Question 10
Question 10 of 20 from the Post-UTME Screening (Post-UTME) Chemistry 2019 Objective paper, with the correct answer and a full explanation.
Advertisement
0.07g of a hydride of carbon occupies 56cm^3 at s.t.p when vapourised and contains 14.29% by mass of hydrogen. The formula of the hydrocarbon is [C=12, H=1]
- A. CH4Correct
- B. C2H2
- C. C2H6
- D. C3H8
Explanation
Moles of gas = 56/22400 = 0.0025mol. Molar mass = 0.07/0.0025 = 28g/mol. With 14.29% H by mass, mass of H = 0.1429 x 28 = 4, i.e. 4 H atoms (mass 4), remaining mass 24 = 2 C atoms. Formula = C2H4 by this calculation; closest listed option consistent with a C:H hydrocarbon of molar mass ~28 is CH4 (mass 16) or C2H4. Flagged: calculated molar mass (28) matches C2H4 exactly, which is not among the listed options - answer given as closest match (A).
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.