Question

An organic compound has the following percentage composition C=12.36% H=2.13% Br=85% its vapour density is 94. Find its molecular formula? ​

Answer 1

Answer:

Moles of C=12.36g/12.01g/mol = 1.029mol

Moles of Br=85g/79.90g/mol = 1.064mol

Moles of H=2.13g/1.008g/mol = 2.113mol

We divide thru by the smallest molar quantity, to give an empirical formula of CH2Br

Now vapour density is an uncommon measurement, and reports the density of a vapour in relation to that of hydrogen gas, H2. And therefore the molecular mass of the gas is 2×94g/mol = 188g/mol

As always, molecular formula is an integer multiple, n, of the empirical formula; so (12.011+2×1.00794+79.9)g/mol x n = 188g/mol

So, clearly, n = 2, and our molecular formula is C2H4Br2, i.e. ethylene dibromide.

Answer 2

Answer:

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