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Question

An acid is a component of rancid butter and has a vile stench. Burning 0.44 g of the acid in excess oxygen yield 0.88 g of CO2 and 0.36 g of H2O as the only products. Given that the acid contains only C, H, and O and if vapour density of the acid is 44, then which of the following options is not correct about it’s molecular formula?

A
It contains 4 carbon atoms
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B
It contains 6 hydrogen atoms
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C
It contains 2 oxygen atoms
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D
Its empirical formula contains 2 carbon atoms
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Solution

The correct option is A It contains 4 carbon atoms
Molar mass=2×vapour density
Given, Vapour density = 44, so molar mass = 88 g/mol.
Since the molar mass of the acid is 88 g so,
0.44 g acid =0.4488=0.005 moles of acid.
Similarly, 0.88 g CO2=0.8844=0.02 mol CO2 & 0.36 g H2O=0.3618=0.02 mol H2O
So 0.005 mols acid contains 0.02 mols of carbon and 0.04 mols of hydrogen.
Hence, 1 mol of acid will contain 4 mol of carbon and 8 mol of hydrogen atoms. So, moles of oxygen will be 88(12×4+1×8)16=2 [since molar mass = 88 g/mol]
So, formula of acid will be C4H8O2.

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