Physical properties

2 marks · Easy

An alkene molecule contains 10 carbon atoms. Calculate the number of hydrogen atoms it contains. Show your working.

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20 (±0)

Must show: working shown

Also accept: C10H20

Common mistakes: 24 (using alkane formula); 18

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Marking points

M1 · 1 mark · Writes or uses general formula CnH2n; substitutes n = 10

A1 · 1 mark · Correctly calculates 10 × 2 = 20 hydrogen atoms

Worked solution

General formula for alkenes: CnH2n

Substitute n = 10: C10H(2×10)

So number of hydrogen atoms = 2 × 10 = 20