Edexcel A-Level Chemistry AS 1.8 Chemical Equations to Calculate Volumes of Gases and Vice Versa Questions

Convert moles and gas volumes at r.t.p., apply stoichiometric ratios, and use pV = nRT with consistent pressure, volume and temperature units for gas calculations.

Exam points

use molar gas volume at r.t.p. with equations to calculate reacting gas volumes
apply pV = nRT after converting pressure, volume and temperature into SI units
link density, mass and moles of a volatile liquid to the volume of gas produced

[Maximum number: 3]

This question is about alkenes.

Bisabolenes are a group of compounds found in plants and fungi. Bisabolene molecules contain several carbon-carbon double bonds.
5.51 g of $\alpha$ -bisabolene reacted with $1873 \mathrm{~cm}^{3}$ of hydrogen gas, $\mathrm{H}_{2}$ . The reaction occured at a temperature of $150^{\circ} \mathrm{C}$ and a pressure of 152000 Pa .
$\left[M_{\mathrm{r}}\right.$ value: $\quad \alpha$ -bisabolene $\left.=204.0\right]$

Calculate the amount, in mol, of hydrogen gas that reacted with $\alpha$ -bisabolene. Use the ideal gas equation, p V=n R T.

\left[R=8.31 \mathrm{~J} \mathrm{~mol}^{-1} \mathrm{~K}^{-1}\right]

rearrangement of ideal gas equation (1)

- conversion of temperature and volume to appropriate units

(1)

- calculation of moles of hydrogen (1)

Example of calculation
$n=\frac{pV}{RT}$

M1 may be subsumed in M3

423( K), 1873 x 10^-6( m^3)

Allow 423( K), 1873 x 10^-3(dm^3), 152(kPa)

Allow 423.15 K (which gives final answer of 0.080963)
$=\frac{(152\times10^{3})\times(1873\times10^{-6})}{8.31\times423}=0.080992\;/\;0.08099\;/\;0.0810\;/\;0.081\;(\mathrm{mol})$

Correct answer with no working scores 1

Allow TE from M2 to M3

Ignore SF except 1SF

Penalise use of 1 SF once only in (c)(i) and (c)(ii)

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Edexcel A-Level Chemistry AS 1.8 Chemical Equations to Calculate Volumes of Gases and Vice Versa Questions question 1