Please help with A level chem question please!

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hanneylooloo
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Two chemical tests are carried out on an aqueous solution of an aromatic organic compound Y.

The results of the tests are shown below.

Test Br2(aq) Na2CO3(aq) Observation decolourised effervescence

What is the minimum number of C atoms in Y?

A 6
B 7
C 8
D 9
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Kian Stevens
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It's B.

An aromatic compound with a carbon count of seven, which satisfies those tests, would have to be one which contains a phenolic group and a -COOH group; the phenolic group can allow the benzene ring to decolourise bromine water, and the -COOH group can effervesce with the carbonate.
(Extra information - this compound is salicylic acid).

It cannot be A. An aromatic compound with a carbon count of six, which can decolourise bromine water, would be phenol; however, phenols don't react with carbonates, so there would be no effervescence. Hence, the -COOH group is necessary for effervescence, and so this will bring the carbon count up to seven.
C and D would simply have excessive carbon atoms.
Last edited by Kian Stevens; 1 year ago
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