Alkanes
2 marks · NormalState the general formula of alkanes and explain what this formula represents.
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The general formula of alkanes is CnH2n+2. This means for every n carbon atoms, there are 2n+2 hydrogen atoms in a molecule of an alkane.
Also accept: C_nH_{2n+2}; The formula CₙH₂ₙ₊₂ (for n = number of carbon atoms)
Common mistakes: Writing CnH2n; Confusing alkane and alkene formulae
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Marking points
B1 · 1 mark · States the correct general formula: CnH2n+2 (or equivalent).
B2 · 1 mark · Explains that it gives the number of H atoms as 2n+2 for n C atoms in any alkane.
Worked solution
The general formula for alkanes is CnH2n+2.
This means that for every n carbon atoms, there are (2n + 2) hydrogen atoms in an alkane molecule.