Chemistry 9701/23 — May/June 2017

Cambridge AS Level · AS Level Structured Questions · worked solutions for every part, with the mark scheme

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Topics Introduction to Organic Chemistry · Hydrocarbons · Atoms, Molecules and Stoichiometry · States of Matter · Group 17 · Electrochemistry · +3 more

Q1Introduction to Organic ChemistryAtoms, Molecules and StoichiometryHydrocarbonsStates of MatterFree sample

Combustion data can be used to calculate the empirical formula, molecular formula and relative molecular mass of many organic compounds. Combustion data cannot distinguish between different structural isomers.

(a)

Define the term structural isomers.

(b)

$\text{P}$ is a hydrocarbon, $\text{C}_x\text{H}_y$ . A gaseous sample of $\text{P}$ occupied a volume of $25\text{ cm}^3$ at $37^\circ\text{C}$ and $100\text{ kPa}$ .

The sample was completely burned in $200\text{ cm}^3$ of oxygen (an excess).
The final volume, measured under the same conditions as the gaseous sample (so that the water produced is liquid and its volume can be ignored), was $150\text{ cm}^3$ .

Treating the remaining gaseous mixture with concentrated alkali, to absorb carbon dioxide, decreased the volume to $50\text{ cm}^3$ .

The equation for the complete combustion of $\text{P}$ can be represented as shown.

\text{C}_x\text{H}_y + \left(x + \frac{y}{4}\right)\text{O}_2 \rightarrow x\text{CO}_2 + \frac{y}{2}\text{H}_2\text{O}

(i)

Use the data given to calculate the value of $x$ .

(ii)

Use the data given to calculate the value of $\left(x + \frac{y}{4}\right)$ .

(iii)

If you were unable to calculate values in (b)(i) and (b)(ii) then use the data in this box for the remaining parts of this question. These are not the correct values.

x = 6 \quad \left(x + \frac{y}{4}\right) = 9

Give the molecular formula and the empirical formula of $\text{P}$ .

(iv)

$\text{P}$ is unbranched.

Give the skeletal formulae for two possible structures of $\text{P}$ that are positional isomers of each other.

Q1_isomers

(v)

Use the general gas equation to calculate the mass of $\text{P}$ present in the original $25\text{ cm}^3$ gaseous sample, which was measured at $37^\circ\text{C}$ and $100\text{ kPa}$ .

Give your answer to three significant figures.

The rest of this paper

3 more questions

Q2Group 17 · Electrochemistry15M
Q3Chemical Energetics · Reaction Kinetics · Equilibria17M
Q4Hydrocarbons · Introduction to Organic Chemistry17M

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