Chemistry 9701 · AS & A Level · Analytical techniques

Analytical techniques — practice question

Compound A is an organic compound containing carbon, hydrogen and oxygen. When $0.240\text{ g}$ of vapour of A is passed slowly over a large excess of heated copper(II) oxide, CuO, compound A is completely oxidised to carbon dioxide and water. Copper is the only further product of the reaction. The products are collected and it is found that $0.352\text{ g}$ of $\text{CO}_2$ and $0.144\text{ g}$ of $\text{H}_2\text{O}$ are produced.
(a)

For this section, give every answer to three decimal places.

(a(i))

Calculate the mass of carbon contained in $0.352\text{ g}$ of $\text{CO}_2$. Use this result to calculate the amount, in moles, of carbon atoms contained in $0.240\text{ g}$ of A.

(a(ii))

Calculate the mass of hydrogen present in $0.144\text{ g}$ of $\text{H}_2\text{O}$. Use this result to calculate the amount, in moles, of hydrogen atoms present in $0.240\text{ g}$ of A.

(a(iii))[6]

Use your answers to calculate the mass of oxygen present in $0.240\text{ g}$ of A. Use this result to calculate the amount, in moles, of oxygen atoms present in $0.240\text{ g}$ of A.

(b)[1]

Use your answers to (a) to calculate the empirical formula of A.

(c)

A $0.148\text{ g}$ sample of A was vapourised at $60^\circ\text{C}$ and the vapour occupied $67.7\text{ cm}^3$ at a pressure of $101\text{ kPa}$.

(c(i))

Use the general gas equation $pV = nRT$ to calculate $M_r$ of A.

(c(ii))[3]

Hence calculate the molecular formula of A.

(d)[2]

Compound A is a liquid that does not react with 2,4-dinitrophenylhydrazine reagent or with aqueous bromine. Suggest two structural formulae for A.

(e)[1]

Compound A is made up only of carbon, hydrogen and oxygen. Explain how the information on the opposite page about the reaction of A with CuO confirms this statement.

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