Chemistry: Post your doubts here!

[kitkat <3 :P]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s04_qp_2.pdf
Q7 n 8 please Suchal Riaz Thought blocker

 

[Suchal Riaz]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s04_qp_2.pdf
Q7 n 8 please Suchal Riaz Thought blocker

which 7 and 8 question? there are only 5 question in that paper dadi

 

[kitkat <3 :P]

Acha :/ ruko I quoted the wrong paper :/ it was 2008 waala sorry

 

[Suchal Riaz]

Acha :/ ruko I quoted the wrong paper :/ it was 2008 waala sorry

again 2008 of summer or winter
parhai ne dimagh kharab kar diya he kya?

 

[_Ahmad]

PLEASE can anyone explain this question!!!!!.
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]

which 7 and 8 question? there are only 5 question in that paper dadi

Yup

 

[sitooon]

What makes you think it'll come?

Guess
I think its tomorrow right? so you will see this question

 

[sitooon]

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

 

[kitkat <3 :P]

Seriously dimaagh khraab hogya hai 7 or 8 page num tha Q5 tha but forget it wo hogya
w08 ka Q1 bii and c part please :/

again 2008 of summer or winter
parhai ne dimagh kharab kar diya he kya?

 

[omaaaar]

I'd go witth something like this

Though, I'm not sure exactly what the full question is. I guess it's asking for NO3- ion

How do you know this might come and if you know anything else pls tell that as well

 

[_Ahmad]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s13_qp_22.pdf

Q5 d i) Can anyone please tell why it is ethanoic acid

 

[Thought blocker]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s13_qp_22.pdf

Q5 d i) Can anyone please tell why it is ethanoic acid

I will follow through the question from beginning to let you know how examiner give you hints.

pattern:
-(information)
the deduction we can make from information

-Q is a sweet smelling liquid.
therefore it is an ester

-Q has Mr of 87.5
mass of C2H4O = 2*12+4+16=44
n=87.5/44~2
so the formula is C4H8O2

now we can see there can be three ester isomers. methyl propanoate, ethyl ethanoate and propyl methanoate. we will see from the following information which isomer it was and then we will go to the original question of finding R.
​

-the solution was hydrolysed. so the carboxyllic acid and alcohol are separated. there can be three kinds of acids and alcohols. methanol, ethanol, propanol, methanoic acid, ethanoic acid and propanoic acid.
- heating with an oxidising agent gives single reagent R
the alcohol will oxidise to produce aldehyde and then will produce carboxyllic acid. as a single compound is formed, both carboxylic acid from ester and oxidised form alcohol are same. the only option we are left with is ethyl ethanoate. which will hydrolyse to ethanol and ethanoic acid. ethanol will then oxidise to ethanal. ethanal will oxidise to ethanoic acid. as the test for C=O and CHO are negative there is no aldehyde. the only thing left is ethanoic acid.

i hope it clears the confusion and helps in reaching conclusions in similar questions.
good luck for the papers ​

 

[Suchal Riaz]

Seriously dimaagh khraab hogya hai 7 or 8 page num tha Q5 tha but forget it wo hogya
w08 ka Q1 bii and c part please :/

(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

 

[Thought blocker]

(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

Ur good in organic, physical or inorganic ?

 

[_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.