Chemistry: Post your doubts here!

[darknessinme]

View attachment 21147
In this question, I know the answer is D but why is C wrong? It does have a chiral centre as well as a carboxylic acid group, so it's both chiral and acidic...

C is an ester, not a carboxylic acid.

 

[!>@/^~^\@<!]

basically over here, room temperature is taken to be "cold conditions" {cold dilute acidified manganate (VII) solution} and under harsher conditions "Hot conditions" is taken to be higher temperatures {hot, concentrated manganate (VII) solution}.

No i was talking about the addition reaction of alkenes (addition of hydrogen halide) not oxidation reaction of alkene...

 

[aalmuhannadi]

C is an ester, not a carboxylic acid.

How do you figure it's an ester? isn't the middle carbon bonded to the left-hand carbon, which has a double bond with oxygen and -OH?

 

[darknessinme]

How do you figure it's an ester? isn't the middle carbon bonded to the left-hand carbon, which has a double bond with oxygen and -OH?

The middle carbon is bonded to the O of the ester group. The compound is made from formic acid reacting with, 1-bromopropan-2-ol to form the ester. Try draw the displayed formula.

 

[aalmuhannadi]

The middle carbon is bonded to the O of the ester group. The compound is made from formic acid reacting with, 1-bromopropan-2-ol to form the ester. Try draw the displayed formula.

Yeah I figured out how to draw it now but how would you tell from its structural formula that it was an ester though? I'm not aware of how it's formed and I don't think you need to know that from the syllabus...

 

[scouserlfc]

i neeed help ! AS questions..

How many isomers with the formula C5H10 have structures that involves pi bonding?
A 3 B 4 C 5 D6

The ans is D !

Its quite easy use chain isomerism + positional isomerism these are basically forms of structural isomerism !
1. CH3CH2CH2CH=CH2
2.CH3CH2CH=CHCH3 + (this is a cis if u keep H on the same side of double bond but trans when different )
3.CH3CH2C(CH3)=CH2
4.CH3CH=C(CH3)CH3
5.CH3CH(CH3)CH=CH2

so here u go 6 isomers !

 

[scouserlfc]

Yeah I figured out how to draw it now but how would you tell from its structural formula that it was an ester though? I'm not aware of how it's formed and I don't think you need to know that from the syllabus...

Actually u need to know how its formed plus some of its conditions and u can easily identify it if u see this group in structural formula ! -COO- or -CO2-
the - meaning its joined to the chain with mostly alcohol in front and Carboxylics chain at the back !

 

[aloha]

does anyone has this guuide!!!!

 

[Student12]

Its quite easy use chain isomerism + positional isomerism these are basically forms of structural isomerism !
1. CH3CH2CH2CH=CH2
2.CH3CH2CH=CHCH3 + (this is a cis if u keep H on the same side of double bond but trans when different )
3.CH3CH2C(CH3)=CH2
4.CH3CH=C(CH3)CH3
5.CH3CH(CH3)CH=CH2

so here u go 6 isomers !

Thanks.. i didnt take the cis trans into consideration.

 

[sweetiepie]

Tips For 31-40 (Chemistry MCQ's Paper 1)

. If 1st choice is obviously incorrect, the answer is automatically C.
. If 2nd choice is obviously incorrect the answer is automatically D.
. If 3rd choice is incorrect and 2nd choice is correct the answer is B.
. If 1st choice and 3rd choice are right the answer is A.

hope this helps

 

[Dukeofwin]

Tips For 31-40 (Chemistry MCQ's Paper 1)

. If 1st choice is obviously incorrect, the answer is automatically C.
. If 2nd choice is obviously incorrect the answer is automatically D.
. If 3rd choice is incorrect and 2nd choice is correct the answer is B.
. If 1st choice and 3rd choice are right the answer is A.

hope this helps

Given the fact you wrote all that, I'll say a Big Thanks! But thats a bit too obvious isnt it? No Offence but its like saying 'if you think A and C are wrong then your answer will either be B or D'

 

[sweetiepie]

Given the fact you wrote all that, I'll say a Big Thanks! But thats a bit too obvious isnt it? No Offence but its like saying 'if you think A and C are wrong then your answer will either be B or D'

what u mean

 

[Dukeofwin]

what u mean

Nevermind! You were a big help. Thanks :/

 

[sweetiepie]

Nevermind! You were a big help. Thanks :/

Welcome

 

[Silent Hunter]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w09_qp_41.pdf

How to do question 7 (c) (ii) ? JazakAllah

 

[unseen95]

please help me with question number 28 of 9701/01/M/J/04 with reason.

 

[scouserlfc]

please help me with question number 28 of 9701/01/M/J/04 with reason.

First remove the formula of benzene from the molecular formula here it is C6H5 so now u have C4H9O which is an alcohol (this differs from the general alcohol formula because one C is bonded to benzene rather than the H ) Now lets see the next requirement it doesnt have to react with mild [O] so basically its a tertiary alcohol ! SO A and B are wrong as they have no side chain ,Now in C its quite obvious that its not the answer as the double bond forms on carbon no 3 from benzene which is wrong as whenever dehydration occurs the OH is removed plus another H is removed from the carbon next door to the OH bonded Carbon and thats not the case so D is the answer !

 

[youssef 98]

do u hve the chemistry oct/nov 2013 papers?

 

[iKhaled]

do u hve the chemistry oct/nov 2013 papers?

we don't even have may/june 2013 yet...

 

[snowbrood]

step 1 if option a is not correct then either option b c or d is correct else go to step 4
step2 if b is also not correct then either option c or d is correct else go to step 4
step 3 if c is also not then d is correct else go to step 4
step 4 that is correct answer
hope that helps it always works for me from mcq 1 to 40