Chemistry: Post your doubts here!

[Metanoia]

Thanks.
But could you explain me using an ionic equation?
The half ionic equation for the concentrated H2SO4 is

2H2SO4 + 2e ----->( SO4)-2 + 2H2O + SO2

So where do H2O and SO2 go ?

You are using a half equation where the concentrated sulfuric acid acts as an oxidizing agent. That does not happen with chlorides (i.e. LiCl).

 

[Mr.Physics]

Can anyone explain how the answer is C? It's says constant speed so shouldn't kinetic energy be constant as well? View attachment 57605

Gravitational energy changes to kinetic energy i think

 

[kayannush99]

Hi, I have a chemistry exam tomorrow. Could someone please explain the answer to Q5, 6, 9, 10, 31, 34 and 35.

Here's the link:
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s10_qp_12.pdf

 

[Sarosh Jameel]

PLZ help me with this! i am unable to questions of polymerisation this is may june 08 !

 

[sj0007]

Will this be the structure of the product when 2-hydroxypropanoic acid reacts with propanoic acid?

 

[qwertypoiu]

Will this be the structure of the product when 2-hydroxypropanoic acid reacts with propanoic acid?
View attachment 57700

Seems correct to me.

 

[sj0007]

Seems correct to me.

Oh hiiiiiiiii!
Thnx........ U helped me out in my IGCSE too!

 

[A*(a*)]

these are the best past papers I came across during my A levels, I do recommend them to everyone, classified past papers upto 2015 with variants included,
https://payhip.com/b/LUjF

 

[Dark Destination]

So what exactly do we have to study to prepare for Paper 4?
Does it include both AS and A2 concepts, or just A2 ones?

For example, do i need to just study A2 organic chemistry (Benzene etc.) or the entire AS organic chemistry as well?

 

[nehaoscar]

Can anyone explain how the answer is C? It's says constant speed so shouldn't kinetic energy be constant as well? View attachment 57605

The answer is not C, it's B ... check the mark scheme again

 

[nehaoscar]

PLZ help me with this! i am unable to questions of polymerisation this is may june 08 !

1. Break the bonds at the peptide linkage (at O=C---NH)
This will give H2NCH2CH2NH2 and HOOCCOOH. This is condensation since water was initially removed to form the polymer.

2. Break the ester bonds
This will give HOCH2CH(CH2CH3)COOH and HOCH2CH(CH3)COOH. This is condensation.

3. There are 3 different sub-parts so just break the bonds and add a double bond to the carbons that had the bonds
This will give CH2=CH-CH3 and CH2=CH-CONH2 and CH2=CH-C6H5(benzene ring). This is addition

 

[bakhita]

So what exactly do we have to study to prepare for Paper 4?
Does it include both AS and A2 concepts, or just A2 ones?

For example, do i need to just study A2 organic chemistry (Benzene etc.) or the entire AS organic chemistry as well?

For Paper 4, we needa revise the entire syllabus both AS and A2. Refer to page 10 of syllabus which, under Paper 4, states:
"...All questions will be based on the A Level syllabus but may require knowledge of material first encountered in the AS Level Syllabus..."

 

[nehaoscar]

So what exactly do we have to study to prepare for Paper 4?
Does it include both AS and A2 concepts, or just A2 ones?

For example, do i need to just study A2 organic chemistry (Benzene etc.) or the entire AS organic chemistry as well?

AS is required ... mainly the organic parts and also some knowledge from the group 2

 

[Aishayasin]

Can anyone tell me how to solve 9702/01/O/N/07 question 10

 

[Mr.Physics]

Can anyone tell me how to solve 9702/01/O/N/07 question 10

The mass of the object is 0.6 kg and its acceleration of 4 m/s^2. So first use F=ma to calculate the force required to accelerate a 0.60 kg mass to 4 m/s^2.

F=ma
F=0.60 x 4= 2.4N

But the force applied is 12N and the force needed to cause this much acceleration is only 2.4 N.
Therefore, the friction force is 12 - 2.4= 9.6N

The answer is D.

 

[nehaoscar]

How is part (ii) Nucleophilic substitution?
Shouldn't it be electrophilic? please explain...

 

[Mr.Physics]

View attachment 57721
How is part (ii) Nucleophilic substitution?
Shouldn't it be electrophilic? please explain...

It's nucleophilic because nitrogen can have 3 bonds and in NH2 it has 2. So it develops are positive charge. When CH3 attacks on it, it's basically attacking a postively charged species. So it's a nucelophilic substituition.

 

[acecie]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w04_ms_4.pdf

qs:6
pls explain why is it E and not D
also explain (b)

TIA

 

[nehaoscar]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w04_ms_4.pdf

qs:6
pls explain why is it E and not D
also explain (b)

TIA

To react with alkali aqueous iodine, it must have CH3C=O group i.e. it must have a methyl ketone group
Only then will iodoform reaction occur replacing the CH3 with CHI3
D has CH3CH2 attached to it instead of just CH3 so it's wrong

b)
I think it's because D has CH3CH2 attached on both sides so it's symmetrical whereas E is not symmetrical

 

[phanttasy]

Need help on this!