In the previous blgopost we have discussed on 3 MCQ questions on Organic Chemistry that came out in 2008 GCE O Levels Chemistry Exams. Let’s continue with the rest of the MCQ questions that are related to Organic Chemistry.
Question 1: under sub-topic “Carboxylic Acids”
The reaction between a carboxylic acid, CxHyCO2H, and an alcohol, CnH2n+1OH, produces an ester.
How many hydrogen atoms does one molecule of the ester contain?
A.? y + 2n
B.? y + 2n + 1
C.? y + 2n + 2
D.? y + 2n + 3PS: Tricky question that ALL Pure Chemistry students must know how to answer
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Question 2: under sub-topic “Carboxylic Acids”
The diagram below shows the structure of ethanoic acid, a carboxylic acid.
CH3COOH
How many moles of ethanoic acid react with one mole of magnesium?
A.? 1
B.? 2
C.? 3
D.? 4
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Question 3: under sub-topic “Alkenes”
The molecular structure of three hydrocarbons are shown below.
Which statement about these hydrocarbons is correct?
A.? All three hydrocarbons are isomers of propene
B.? R is a branched alkene
C.? S is but-1-ene
D.? T is an isomer of butene
PS: Do attempt the questions and leave your answers & suggested reasoning in the ?Leave A Reply? section below
PPS: If you would like more Tips, Notes and Questions on Organic Chemistry, please check out the archives (older blogposts) by CLICKING HERE
for the 3rd question, the answer should be D.
A and B have been eliminated for the reasons already stated by others earlier.
As for C,
S should be but-2-ene if i’m not wrong.
I’m not very sure so if anyone knows please please correct me! (:
I think it’s b, b, c? Not too sure about the last though..
i agree with TKS that the answers are
1)B
2)B
3)D
for 2) when balanced the equation of reaction between ethanoic acid and magnesium so we will see that 2 moles of ethanoic acid is reacting with magnesium.
for 3)D IS THE CORRECT ANS BECAUSE ISOMERS ARE DRAWN BY CHANGING THE POSITION.
pl z tell if i m wrong or the explanation i have given is wrong.
i think the answer is
Q1 : B
Q2 : B
Q3 : D
i try to explain how i get my answer, but if i am wrong please quickly tell me, cuz i am no good at this chapter
Q1 : B is y + 2n + 1
at first i thought it is y + 2n + 3, but then i forgot that when ester are formed, the hydrogen are taken out from both the carboxylic acid and alcohol, so left with only y + 2n + 1
Q2 : i think this is just a simple mole calculation question.
the equation goes like this
2CH3COOH + Mg ——> (CH3COO)2MG + H2
therefore, ratio of Mg is to CH3COOH is 1 is to 2,
and thus the no. of mol of CH3COOH needed to react with one mole of Mg is 2 x 1 = 2mol
Q3 :
i do not really know how to do this question, i just guess by eliminating, for option A, it is definitely wrong because that the hydrocarbons has 4 carbon, which is butene.
option B, R and T are not branched, so option B is out
Option C, i do not really know wat is means by but-1-ene, but it seems like butene is the only way of saying S. so i decided to choose option D
also, despite the way my teacher taught me, i still managed to vaguely recognise how isomers look like.. so i think Option D is correct.
once again, pls tell me if i am wrong in anything thing i tried explaining.
Cheers
KS
ans is A??
answers pliz