Chemistry: Post your doubts here!

[_Ahmad]

Thanks a lot for your explanation it really helped.
can you please help me with this question also, I had posted it three times but there is no answer yet
calculate average bond energy of C-C bond in ethane given ΔHf(C2H6) = -85 KJ/mol , ΔHat(H)gas =218 KJ/mol and ΔHat(graphite) = 715 KJ/mol

 

[Thought blocker]

Thanks a lot for your explanation it really helped.

can you please help me with this question also, I had posted it three times but there is no answer yet
calculate average bond energy of C-C bond in ethane given ΔHf(C2H6) = -85 KJ/mol , ΔHat(H)gas =218 KJ/mol and ΔHat(graphite) = 715 KJ/mol

I suck at chemistry, sorry/

 

[Adiizz]

What is meant by heating to a constant mass? This term is often used in Paper 5. The question was that how you would ensure that decomposition is complete and the answer suggested heating to a constant mass. Any idea people? Thank You

It means that you have to continue the process of heating and weighing until the mass remains constant. This is to ensure that the reaction is complete..

 

[Suchal Riaz]

Suchal Riaz
How to balance by oxidation no. ? Any help ?
Eg, View attachment 41408

 

[AbbbbY]

your answer is right , but how did you figure out that one will be double and the other two will be single bond?

Any of them can be double. It's a 3D structure.

You've to understand that NO3- is coming from HNO3. One oxygen has a double bond, one oxygen is datively bonded and one oxygen is normally bonded. This last oxygen is the one which will have the electron shown by a square as it's the one bonded that was bonded to Hydrogen. Makes sense?

 

[AbbbbY]

Thanks a lot for your explanation it really helped.
can you please help me with this question also, I had posted it three times but there is no answer yet
calculate average bond energy of C-C bond in ethane given ΔHf(C2H6) = -85 KJ/mol , ΔHat(H)gas =218 KJ/mol and ΔHat(graphite) = 715 KJ/mol

Could you please link me to the paper, or a screenshot of the exact entire question please.

 

[_Ahmad]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_22.pdf

Can anyone please explain Q1 especially Q1 (c) i).

 

[_Ahmad]

Could you please link me to the paper, or a screenshot of the exact entire question please.

Sorry but there is no such question in the pastpapers and this is the entire question which i have.

 

[kitkat <3 :P]

(b)(ii)
one mol of diesel requires 23 mol of O2. one mol of H2O2 produce 1/2 moles of O2. so it 2*23 = 46 mol of H2O2 will be required
(c)
Mr = (15*12)+32=212
mass = 212 tonnes = 212X10^6 grams
n(diesel)=mass/mr=212X10^6 grams /212=1X10^6 mol
n(H2O2)=(46)*n(diesel)=46* 1X10^6=46X10^6 moles
Mr of H2O2=2+16+16=34
Mass of H2O2 = n(H2O2)*34=46X10^6*32=1564X10^6 grams = 1564 tonnes

Thank u

 

[Haya Ahmed]

what do we call nucleiphiles and electrophiles .. atoms or molecules or compounds or elements or substances

 

[asma tareen]

what do we call nucleiphiles and electrophiles .. atoms or molecules or compounds or elements or substances

i think they can be both ions and atoms as nucleophiles are species that can be anions or any electron defiecient atom
while electrophile can be cation :/

 

[Haya Ahmed]

i think they can be both ions and atoms as nucleophiles are species that can be anions or any electron defiecient atom
while electrophile can be cation :/

In definition what am I supposed to say !

 

[omaaaar]

In definition what am I supposed to say !

The definition given in the book is
An electrophile is an acceptor of a pair of electrons
A nucleophile is a donator of a pair of electrons

 

[AbbbbY]

Sorry but there is no such question in the pastpapers and this is the entire question which i have.

So then where did you get this question. It has insufficient detail. I believe the full question will have something to do with graphite.

 

[AbbbbY]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_22.pdf

Can anyone please explain Q1 especially Q1 (c) i).

Easy question. Been asked here quite a lot recently.

Look, moles of NaOH used = 0.045
Moles of NaOH that react with HCl = 0.005

The remaining NaOH is what reacted with the acid so acid remaining = 0.040

Equilibrium concentrations = 0.04 0.04 0.06 0.06
If you don't get the abridged explanation let me know and I'll go step by step.

BTW, anyone A2 will tell you this is an incorrect question as the NaOH will hydrolyse the ester formed but let's just assume it magically doesn't.

 

[Suchal Riaz]

what do we call nucleiphiles and electrophiles .. atoms or molecules or compounds or elements or substances

Species is the correct word

 

[MYLORD]

Which Exam paper is this ?

How to draw this :
PS : As students take care , this might be the question for you this session !!!
View attachment 41393

 

[Dexterwarrior12]

What about nmr spectroscopy in A2? Like, should I be memorising the Peaks at certain chmical shifts?

 

[Browny]

Can anyone please give me marking scheme explanations for what are electrophiles, nucleophiles and free radicals?

 

[AbbbbY]

How to draw this :
PS : As students take care , this might be the question for you this session !!!
View attachment 41393

I was practicing P4's and I just came across this. Why would it pop up in AS if it's in P4 :/