Chemistry 9701 · AS & A Level · Hydroxy compounds

Hydroxy compounds — practice question

Combustion data may be used to work out the empirical formula, molecular formula and relative molecular mass of many organic compounds.
(a)[2]

Define relative molecular mass.

(b)

T is an alcohol, $\text{C}_x\text{H}_y\text{O}$. A gaseous sample of T had a volume of $20\,\text{cm}^3$ at $120\,^{\circ}\text{C}$ and $100\,\text{kPa}$. It was completely burned in $200\,\text{cm}^3$ of oxygen, which was in excess. The final volume, taken under the same conditions as the gaseous sample, was $250\,\text{cm}^3$. Under these conditions, any water present is vapour. When the water vapour was removed from the gaseous mixture, the volume fell to $170\,\text{cm}^3$. Treating the remaining gaseous mixture with concentrated alkali to absorb carbon dioxide reduced the volume to $110\,\text{cm}^3$. The equation for the complete combustion of T can be represented as shown: $\text{C}_x\text{H}_y\text{O} + z\text{O}_2 \rightarrow x\text{CO}_2 + \frac{y}{2}\text{H}_2\text{O}.$

(b(i))[1]

From the data provided, calculate the value of $x$.

(b(ii))[1]

From the data provided, calculate the value of $y$.

(b(iii))[1]

Complete the equation for the complete combustion of alcohol T: $\dots + \dots\text{O}_2 \rightarrow \dots\text{CO}_2 + \dots\text{H}_2\text{O}$.

(b(iv))[2]

Give the skeletal formulae for two possible structures of T, then name each alcohol.

(b(v))[3]

Use the general gas equation to work out the mass of T in the original $20\,\text{cm}^3$ gaseous sample, which was measured at $120\,^{\circ}\text{C}$ and $100\,\text{kPa}$. Give your answer to three significant figures and show the working.

Worked solution & mark scheme

This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: The mass of a single molecule OR the (weighted) average / (weighted) mean mass of the molecules

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