Q59 · Practice questionComplex familiar5 marks
QUESTION 59 (5 marks)
A liquid contains 60.0% carbon, 13.3% hydrogen and 26.7% oxygen by mass. Its molar mass is approximately 60.0 g mol⁻¹. Use atomic masses C = 12.0, H = 1.00, O = 16.0.
a) Determine its empirical and molecular formulas. [3 marks]
b) Give two alcohol structural isomers consistent with the molecular formula. [2 marks]
WORKED SOLUTION
5 marksPractice marking scheme
Empirical and molecular formula ; propan-1-ol and propan-2-ol.
For 100 g, mole amounts are 5.00 C, 13.3 H and 1.669 O. Divide by 1.669 to obtain approximately 3:8:1. The empirical mass is 60.0, so the molecular formula is the same. The hydroxyl group can be on carbon 1 or carbon 2.
- Converts percentage masses to mole amounts. [1 marks]
- Obtains empirical ratio 3:8:1. [1 marks]
- Uses molar mass to confirm C₃H₈O. [1 marks]
- Gives propan-1-ol structure/name. [1 marks]
- Gives propan-2-ol structure/name. [1 marks]
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