The density of an unknown gas is $$$0.656 \mathrm{~g} \mathrm{dm}^{-3}$$$ at $$$20^{\circ} \mathrm{C}$$$ and 101000 Pa . $$$\left[p V=\mathrm{n} R T \quad R=8.31 \mathrm{Jmol}^{-1} \mathrm{~K}^{-1}\right]$$$ (a) Calculate the molar mass of the unknown gas. (5) (b) The unknown gas is a hydrocarbon. Give the name or formula for the unknown gas using your answer to (a). (1) ................................................................................................................................................................................................................................................................................

Chemistry

IGCSE&ALevel

EDEXCEL

Exam No：wch11-01-que-20240111 Year：2024 Question No：IGCSE&ALevelChemistry2024AS0505

Answer:

- conversion of $\mathrm{dm}^{3}$ to $\mathrm{m}^{3}$
- conversion of temperature to K
- rearrangement of ideal gas equation
- evaluation to give number of moles
- calculation of molar mass
Alternative method
- conversion of any volume in $\mathrm{dm}^{3}$ to $\mathrm{m}^{3}$ by dividing by 1000 (e.g. 24 in this case)
- conversion of temperature to K
- rearrangement of ideal gas equation
- evaluation to give number of moles
- calculation of mass in volume chosen in M1 (eg 24 $\mathrm{dm}^{3}$ as shown)
and
calculation of molar mass
An answer that makes reference to the following point:
- methane/CH4

Knowledge points:

1.Formulae, Equations and Amount of Substance

4.Introductory Organic Chemistry and Alkanes

Solution:

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