No topics match this filter.
Practise 26 exam-style questions on Crude oil, hydrocarbons and alkanes for AQA GCSE Chemistry. Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.
Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.
Name the alkanes with these molecular formulae:
C₂H₆
C₄H₁₀
C₂H₆ is ethane.
C₄H₁₀ is butane.
The first four alkanes are methane (1 carbon), ethane (2), propane (3) and butane (4). The '-ane' ending shows an alkane; be careful not to write '-ene', which is the ending for alkenes.
C₂H₆: ethane
do not accept ethene
C₄H₁₀: butane
do not accept butene
Propane has the molecular formula C₃H₈.
State the number of carbon-carbon (C-C) bonds and the number of carbon-hydrogen (C-H) bonds in one molecule of propane.
There are 2 C-C bonds (joining the three carbon atoms in a chain) and 8 C-H bonds (one to each hydrogen atom).
In the displayed formula of propane, the three carbon atoms are joined in a chain by two single bonds, and every hydrogen atom is joined to a carbon atom by one single bond, so there are as many C-H bonds as hydrogen atoms.
2 C-C bonds
8 C-H bonds
The table shows information about the first four alkanes.
Relative atomic masses (Ar): C = 12, H = 1
Determine X, Y and Z.
X: Mr of C₂H₆ = (2 × 12) + (6 × 1) = 30
Y: propane has 3 carbon atoms, so (2 × 3) + 2 = 8 hydrogen atoms: C₃H₈
Z: Mr of C₄H₁₀ = (4 × 12) + (10 × 1) = 58
Use the general formula CₙH₂ₙ₊₂ to find the molecular formula from the number of carbon atoms, and add up the relative atomic masses to find Mr. Each alkane's Mr is 14 more than the one before, which is a useful check.
X = 30
correct answer with no working scores full marks
Y = C₃H₈
allow C3H8
Z = 58
A molecule of an alkane contains a total of 29 atoms.
Relative atomic masses (Ar): C = 12, H = 1
Determine the molecular formula of the alkane and calculate its relative formula mass (Mr).
An alkane CₙH₂ₙ₊₂ contains n carbon atoms and 2n + 2 hydrogen atoms.
total atoms = n + 2n + 2 = 3n + 2 = 29
3n = 27, so n = 9
molecular formula = C₉H₂₀
Mr = (9 × 12) + (20 × 1) = 108 + 20 = 128
Set up an expression for the total number of atoms using the general formula and solve it. Check your answer: 9 + 20 = 29 atoms.
n + (2n + 2) = 29 / 3n + 2 = 29
allow trial and improvement using alkane formulae; correct answer with no working scores full marks
n = 9
C₉H₂₀
allow ecf from an incorrect value of n
Mr = (9 × 12) + (20 × 1) = 128
allow ecf from an incorrect formula
Ready to try the rest? Every answer you write is marked against the mark scheme, so you can see exactly where the marks are.
Hi! Stuck? Ask me for a hint and I’ll help you work it out. Once you’ve checked your answer I can explain exactly where the marks are.
