Physical properties
2 marks · HardState the general formula for alkenes. Explain, using your formula, how you can determine the number of hydrogen atoms in an alkene containing 9 carbon atoms.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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Also accept: The general formula is CnH2n; to find the number of hydrogens, double the number of carbons: for n = 9, it is H18.
Common mistakes: Giving alkane formula instead of alkene; Using n+2 hydrogens
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Marking points
B1 · 1 mark · States the general formula for alkenes as CnH2n or equivalent.
B2 · 1 mark · Explains that the number of hydrogen atoms is twice the number of carbon atoms, or substitutes n = 9 in CnH2n and gets 18 hydrogens.
Worked solution
The general formula for alkenes is CnH2n.
To find the number of hydrogen atoms for an alkene with 9 carbon atoms, substitute n = 9 into the formula:
So, an alkene with 9 carbon atoms has 18 hydrogen atoms.