The test for unsaturated compounds
2 marks · EasyA student tests an unknown hydrocarbon with bromine water. The liquid does not decolourise bromine water. Explain what this result tells you about the type of hydrocarbon and give a reason.
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The hydrocarbon is an alkane; alkanes do not decolourise bromine water because they are saturated and do not have a carbon–carbon double bond.
Also accept: It is saturated; There is no C=C double bond; It is not an alkene
Common mistakes: It is an alkene; It is unsaturated
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Marking points
B1 · 1 mark · Correctly identifies the hydrocarbon as an alkane/saturated/does not contain C=C double bond.
B1 · 1 mark · Reason given: alkanes do not react with bromine water because they contain only single bonds/are saturated.
Worked solution
If the hydrocarbon does not decolourise bromine water, it is an alkane (or a saturated compound). This is because alkanes do not react with bromine water, as they do not have a carbon–carbon double bond.