Chemistry hydrogenation question
The question is here: https://ibb.co/iDvS6T
I am unsure how to work out the correct answer which the mark scheme says is C (Oleic acid).
I understand that moles of H2 = 10.8/24 = 0.45 mol but I don't get how to relate that to the fatty acid. I understand that one molecule of H2 will add across 1 double bond.
We are not given the structures of these molecules either. Please only leave an answer if you have viewed the question on the url!!
I am unsure how to work out the correct answer which the mark scheme says is C (Oleic acid).
I understand that moles of H2 = 10.8/24 = 0.45 mol but I don't get how to relate that to the fatty acid. I understand that one molecule of H2 will add across 1 double bond.
We are not given the structures of these molecules either. Please only leave an answer if you have viewed the question on the url!!
Original post by splitter2017
The question is here: https://ibb.co/iDvS6T
I am unsure how to work out the correct answer which the mark scheme says is C (Oleic acid).
I understand that moles of H2 = 10.8/24 = 0.45 mol but I don't get how to relate that to the fatty acid. I understand that one molecule of H2 will add across 1 double bond.
We are not given the structures of these molecules either. Please only leave an answer if you have viewed the question on the url!!
I am unsure how to work out the correct answer which the mark scheme says is C (Oleic acid).
I understand that moles of H2 = 10.8/24 = 0.45 mol but I don't get how to relate that to the fatty acid. I understand that one molecule of H2 will add across 1 double bond.
We are not given the structures of these molecules either. Please only leave an answer if you have viewed the question on the url!!
You worked out 0.45 mol of hydrogen. 1 mol of hydrogen saturates 1 mol of pi bonds, so the number of pi bonds saturated is 3 (0.45 / 0.15).
An alkene's general formula is CnH2n, so the only fatty acid which satisfies this equation is C (oleic acid). Oleic acid has a single pi bond because of this. Since it's a triester of oleic acid, there will be a total of 3 pi bonds, hence why 0.45 mol of hydrogen was needed to completely hydrogenate 0.15 mol of triester.
Additional information: A and D are alkanes, as they satisfy the alkane formula, CnH2n+2. B is a diene, since 2 hydrogen atoms are lost with each added pi bond - if B was an alkane it would have 36 hydrogen atoms altogether, however it only has 32, so the difference of 4 hydrogen atoms means it's a diene and so twice the amount of hydrogen would be needed to completely hydrogenate it.
(edited 5 years ago)
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