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Chemistry: Post your doubts here!

roxylara

roxylara

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Guys I need help in the practicals. How much time do I allocate if there's 3 questions. Like complete each experiment in 20 maximum 30 minutes and leave the rest for calculations? I really suck at moles but do the moles in the exam papers are they all really similar or same? I'd appreciate any tips :)
 
AbbbbY

AbbbbY

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NinjaInPyjamas said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_qp_2.pdf

help with 5(b) and (c) iii please?
Click to expand...

Is this crazy co-incidence or what? I was hoping it'd be this question haha.

5b)

C4H8O2.

HCO2CH2CH2CH3
CH3CO2CH2CH3
CH3CH2CO2CH3
HCO2CH(CH3)2

Ofcourse, now any of them can be W X Y and Z.

c(i): Carbonyl group
(ii): Ketone is present
(iii) Reverse solve this question. Look. Since part c(ii) tells us it has a ketone group when oxidised, it has to be a secondary alcohol. See the esters you made. In the ones I made, the 4th one uses a secondary alcohol.

So, HOCH(CH3)2
 
A

Abdel Moniem

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AbbbbY said:
Umm, you do realize you've answered 24 here, right? :p
Thank you for you help :D

quote="Suchal Riaz, post: 745892, member: 15977"]there are two c=c so two moles of Br2 are required to react completely. and (separately) 2 mol of h2 are required.
Click to expand...

A!

This is a pretty simple question which idk why a lot of students have trouble answering.

Tackle it like this.

If the compound was an alkane and had no rings or double bonds, number of H atoms present = 2n+2 = 2(20)+2 = 42

Now, every time there're 2H less, you'll either have a double bond or a ring. The question states that there's one aldehyde (C=O) and 1 ring structure which has 1 C=C so this accounts for 6 missing Hydrogens, thereby leaving you with 8 missing Hydrogens.

8/2 = 4 Hydrogens in the aliphatic side chain.

However, total C=C are 5 because you have to include the C=C from the cyclohexene + cis formation hence A[/quote]
 
A

A star

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roxylara said:
Guys I need help in the practicals. How much time do I allocate if there's 3 questions. Like complete each experiment in 20 maximum 30 minutes and leave the rest for calculations? I really suck at moles but do the moles in the exam papers are they all really similar or same? I'd appreciate any tips :)
Click to expand...
complete dependedt on the paper . My paper required 30 minutes per experiment but in some cases you may need to spend more time in the titration dividing time like 45-20-25 something cause they will give a shorter experiment with a longer one
 
N

NinjaInPyjamas

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AbbbbY said:
Is this crazy co-incidence or what? I was hoping it'd be this question haha.

5b)

C4H8O2.

HCO2CH2CH2CH3
CH3CO2CH2CH3
CH3CH2CO2CH3
HCO2CH(CH3)2

Ofcourse, now any of them can be W X Y and Z.

c(i): Carbonyl group
(ii): Ketone is present
(iii) Reverse solve this question. Look. Since part c(ii) tells us it has a ketone group when oxidised, it has to be a secondary alcohol. See the esters you made. In the ones I made, the 4th one uses a secondary alcohol.

So, HOCH(CH3)2
Click to expand...

perfect coincidence haha. thanks!
 
N

NinjaInPyjamas

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Attal Khan said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w13_qp_11.pdf
question 5
check out the er......the explanation seems wrong to me
Click to expand...
are you confused about the catalyst being produced? in the question, they say that the product catalyses the reaction. so as more product is formed, the reaction is faster. after some time though, reactants would be used up, so then there would be no use for catalyst so rate of reaction decreases.
 
AbbbbY

AbbbbY

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NinjaInPyjamas said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s08_qp_2.pdf

1(b) (d) and 5 (e)
Click to expand...

1b:
If I'm not mistaken,
Ethanal: A
Ethanol: C
Methoxymethane: A
2-methylpropane: B

Not sure though. If I'm wrong, do let me know.

1d:
I'd probably go along the lines of Hydrogen bonding.

I'd write that ethoxyethane cannot form hydrogen bonds with water so two insoluble layers are formed.

That'd get me one mark I think. Not sure what the second mark is for.

5e:
So you basically need a di-ol.

ethanedial is CHOCHO so COHCOH pretty much. The displayed structure would have an alkyne with 2 OH R Groups

OH-C=-C-OH

=- <= triple bond.
 
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