QQuestion
An organic compound ‘X’ contains carbon, oxygen and hydrogen only. The percentage of carbon and hydrogen are 47.4% and 10.5% respectively. The relative molecular mass of ‘X’ is 76. Find the empirical formula and the molecular formula of ‘X’.
[ Atomic weight: C = 12, O = 16, H = 1 ]
✓Answer
| Element | Percentage composition | Atomic weight | Relative number of atoms | Simplest ratio |
|---|---|---|---|---|
| C | 47.4 | 12 | \frac{47.4}{12}=3.95 | \frac{3.95}{2.63}=\frac{3}{2} |
| H | 10.5 | 1 | \frac{10.5}{1}=10.5 | \frac{10.5}{2.63}=4 |
| O | 42.1 | 16 | \frac{42.1}{16}=2.63 | \frac{2.63}{2.63}=1 |
Simplest ratio C : H : O = \frac{3}{2}:4:1=3:8:2
Empirical formula = C3H8O2
Empirical formula weight = (3 × 12) + (8 × 1) + (2 × 16) = 76
Relative molecular mass = 76
Molecular formula = C3H8O2
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