Chemistry 9701/21 — May/June 2017

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

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Topics States of Matter · Hydrocarbons · Introduction to Organic Chemistry · Atoms, Molecules and Stoichiometry · Hydroxy Compounds · Chemical Bonding · +7 more

Q1Atoms, Molecules and StoichiometryStates of MatterHydrocarbonsHydroxy CompoundsIntroduction to Organic ChemistryFree sample

Combustion data can be used to calculate the empirical formula, molecular formula and relative molecular mass of many organic compounds.

(a)

Define the term relative molecular mass.

(b)

T is an alcohol, $\text{C}_x\text{H}_y\text{O}$ . A gaseous sample of T occupied a volume of $20\text{ cm}^3$ at $120\text{ }^\circ\text{C}$ 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, was $250\text{ cm}^3$ .

Under these conditions, all water present is vaporised. Removal of the water vapour from the gaseous mixture decreased the volume to $170\text{ cm}^3$ .

Treating the remaining gaseous mixture with concentrated alkali, to absorb carbon dioxide, decreased 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}

(i)

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

$x = \text{..............................}$

(ii)

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

$y = \text{..............................}$

(iii)

If you were unable to calculate values for $x$ and $y$ then use $x = 4$ and $y = 10$ for the remaining parts of this question. These are not the correct values.

Complete the equation for the complete combustion of the alcohol, T.

\text{............................} + \text{.................O}_2 \rightarrow \text{.................CO}_2 + \text{.................H}_2\text{O}

(iv)

Give the skeletal formulae for two possible structures of T.

Name each alcohol.

(v)

Use the general gas equation to calculate the mass of T present in the original $20\text{ cm}^3$ gaseous sample, which was measured at $120\text{ }^\circ\text{C}$ and $100\text{ kPa}$ .

Give your answer to three significant figures. Show your working.

$\text{mass} = \text{.............................. g}$

The rest of this paper

3 more questions

Q2Chemical Bonding · States of Matter · Chemical Energetics · Equilibria15M
Q3Chemical Periodicity · Atomic Structure · Group 2 · Group 1716M
Q4Introduction to Organic Chemistry · Hydrocarbons · Carbonyl Compounds19M

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