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Chemistry

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]

Stoichiometry

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Answer

Element% compositionAt. wt.Relative no. of atomsSimplest ratio
Carbon47.41247.412\dfrac{47.4 }{12} = 3.953.952.63\dfrac{3.95}{2.63 } = 32\dfrac{3 }{2}
Hydrogen10.5110.51\dfrac{10.5}{1} = 10.510.52.63\dfrac{10.5}{2.63 } = 4
Oxygen42.11642.116\dfrac{42.1}{16} = 2.632.632.63\dfrac{2.63}{2.63 } = 1

Simplest ratio of whole numbers = C : H : O = 32\dfrac{3}{2} : 4 : 1 = 3 : 8 : 2

Hence, empirical formula is C3H8O2

Empirical formula weight = (3 x 12) + (8 x 1) + (2 x 16)= 36 + 8 + 32 = 76

Empirical formula weight = Relative molecular mass = 76

So, molecular formula = C3H8O2

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