Chemistry: Post your doubts here!

[VelaneDeBeaute]

i cant do most of the questions on aldehydes,ketones,carboxylic acids, alcohols and esters on P1 and P2. My problem is that they ask for substances i've never seen. plz tell me an easy way of solving questions like these.

Hey, don't freak out on seeing alien compounds. That will a part of the exam most of the times. You just need a knowledge of the functional groups. Forget whatever the R chains must be, just focus on how the functional groups are interacting.

 

[A*(a*)]

View attachment 23074
Can you answer this also please? Its from the same year and variant is 13.

Hey, don't freak out on seeing alien compounds. That will a part of the exam most of the times. You just need a knowledge of the functional groups. Forget whatever the R chains must be, just focus on how the functional groups are interacting.

Can you help me doing this question?

 

[VelaneDeBeaute]

Can you help me doing this question?

Knowing that I solved the same question last year, it yet proved a challenge for me.
Anyway, Let's look at the options.
(A) Correct; First Equation worked backwards shows that it accepts the H+ (is a base) and forms H2SO3 which further decomposes to H2O and SO2.
(B) Wrong; SO2 acts as reducing agent, proven by the fact that it accepts the H+. (1st Equation)
(C) Wrong: It accepts a proton (2nd Equation backwards) which is a characteristic of bases.
(D) Wrong; It acts as an oxidizing agent and is itself reduced.

If my answer is wrong, do let me know so I can check my thinking again!

 

[A*(a*)]

your answer is correct. May God bless you, thankyou soo much - I never knew H2SO3 can decompose like this! According to examiner how am I supposed to know this? Which topic is it related to? :/

 

[A*(a*)]

And can anyone on Earth tell me what am I missing in this question?
The refrence is 9701/12/M/J/11 [ U can check the markscheme, the answer is A. How is 1 correct ?!!!

 

[Muhammad Bin Anis]

And can anyone on Earth tell me what am I missing in this question?
The refrence is 9701/12/M/J/11 [ U can check the markscheme, the answer is A. How is 1 correct ?!!!
View attachment 23077

In NCl3, the oxidation state of nitrogen is +3 (x + 3(-1) = 0)
and in N2 its 0.
Nitrogen is reduced so it ought to be redox reaction.

 

[snowbrood]

In NCl3, the oxidation state of nitrogen is +3 (x + 3(-1) = 0)
and in N2 its 0.
Nitrogen is reduced so it ought to be redox reaction.

why is COSe more polar than COS molecule

 

[Muhammad Bin Anis]

why is COSe more polar than COS molecule

probably because of the greater electronegativity difference.

In either of the cases C and O bond is present.
what differs is the other part .

Se is further down the group and does not attracts the bonding pair of electrons as much as the oxygen.
even Sulphur is also not as electronegative as the Oxygen but the electronegativity gap is reduced.
Hence COSe is more polar

 

[Muhammad Bin Anis]

snowbrood i dont think your question was related to the redox ques previously asked... still you qouteed that answer

 

[aseelz]

Salaam w Allikum people
can someone pleeeeeeease tell me how to solve Q10 in nov'12 paper 1???

Q: a student calculated the standard enthalpy change of formation of ethane using a method based on standtard enthalphy change of combustion. he used correct values for standard enthalpy change of combustion of ethane(-1560) and hydrogen(-286) but he used incorrect value for standard enthalpy change of formation of carbon. he then performed his calculation correctly. his final answer was -158KJ/mol

what did he use for standard enthaly change of combustion of carbon?
A)-1432
B)-860
C)-430
D)-272
???????
if he used a wrong value then it can be anyone of the four choices?? anyone?? please help i cant understand this...thank uuuuuuuuuuu in advance

 

[A*(a*)]

In NCl3, the oxidation state of nitrogen is +3 (x + 3(-1) = 0)
and in N2 its 0.
Nitrogen is reduced so it ought to be redox reaction.

Thanks for your help but according to your answer doesn't N undergoes 'reduction'? Isn't there any difference in reduction and redox? I guess the question is about disproportionation?

 

[Muhammad Bin Anis]

Thanks for your help but according to your answer doesn't N undergoes 'reduction'? Isn't there any difference in reduction and redox? I guess the question is about disproportionation?

the word redox has its roots from the two words REDuction and OXidation.
In a redox reaction, one specie oxidises while the other reduces.

How come you squeeze disproportionation here? The question doesnt give a clue about it...

 

[ZainH]

the word redox has its roots from the two words REDuction and OXidation.
In a redox reaction, one specie oxidises while the other reduces.

How come you squeeze disproportionation here? The question doesnt give a clue about it...

Hm, option one states that "NITROGEN, undergoes a redox reaction"

Isn't nitrogen only reduced? Redox means both oxidation and reduction right?

 

[VelaneDeBeaute]

Hm, option one states that "NITROGEN, undergoes a redox reaction"

Isn't nitrogen only reduced? Redox means both oxidation and reduction right?

Well, Nitrogen can undergo a Redox reaction even if it is only being reduced.
This is because a Redox reaction is one where *one species* is oxidised and the *other* is reduced. It doesn't have to be the *same species*.

 

[unseen95]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_41.pdf question number 3(e) with explanation

 

[A*(a*)]

the word redox has its roots from the two words REDuction and OXidation.
In a redox reaction, one specie oxidises while the other reduces.

How come you squeeze disproportionation here? The question doesnt give a clue about it...

Well, Nitrogen can undergo a Redox reaction even if it is only being reduced.
This is because a Redox reaction is one where *one species* is oxidised and the *other* is reduced. It doesn't have to be the *same species*.

Its okay guys
I thought that with the word redox, we were supposed to see that whether nitrogen undergoes reduction and oxidation both... which is the case in disproportionation

 

[snowbrood]

probably because of the greater electronegativity difference.

In either of the cases C and O bond is present.
what differs is the other part .

Se is further down the group and does not attracts the bonding pair of electrons as much as the oxygen.
even Sulphur is also not as electronegative as the Oxygen but the electronegativity gap is reduced.
Hence COSe is more polar

i still dont get it

 

[Muhammad Bin Anis]

i still dont get it

Can you repeat the question in a bit more explained way?
Ill try to explain

 

[snowbrood]

Can you repeat the question in a bit more explained way?
Ill try to explain

what is electronegativity gap

 

[Muhammad Bin Anis]

what is electronegativity gap

I meant the difference in the electronegativities of the two elements