O Levels Chemistry 2008 Exam Question: Organic Chemistry in Paper 1 (MCQs)-Cont’d

14 Jul

Posted by: sean in: Chemistry Notes & Tips

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 + 3

PS: Tricky question that ALL Pure Chemistry students must know how to answer

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

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

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5 Responses

paul
02|Aug|2009 1

answers pliz

Reply
A0
07|Aug|2009 2

ans is A??

Reply
TKS
24|Aug|2009 3

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

Reply
daphney
06|Oct|2009 4

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.

Reply
M
08|Oct|2009 5

I think it’s b, b, c? Not too sure about the last though..

Reply