Chemistry: Post your doubts here!

[Lujain M.]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s13_qp_13.pdf please help in q 8

 

[Rockstar RK]

i meant moles of ethanol and ethanoic acid

Q26) When an isomer Y of molecular formula C4H9Br undergoes hydrolysis in aqueous alkali to form
an alcohol C4H9OH, the rate of reaction is found to be unaffected by changes in the concentration
of OH– ions present.
Which is the most likely molecular structure of Y?
A CH3CH2CH2CH2Br
B CH3CH2CHBrCH3
C (CH3)2CHCH2Br
D (CH3)3CBr
Pls solve dis

 

[Suchal Riaz]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s13_qp_11.pdf Q11 ansB Q20 ansB Q30 ansB

Sn is oxidised from2+ to 4+ so change in oxidation number=+2
Mn changes from +6 to +2 so change in oxidation number = -4
so there must be two moles of Sn for each mole of MnO4 to balance change in oxidation state.

 

[♣♠ Magnanimous ♣♠]

i meant moles of ethanol and ethanoic acid

but i was talking about the water and ethyl ethanoate... it means when there is no units we can take 1?

 

[ZaqZainab]

i meant moles of ethanol and ethanoic acid

yup so why did you take 1 mole of H20?

 

[Suchal Riaz]

Q26) When an isomer Y of molecular formula C4H9Br undergoes hydrolysis in aqueous alkali to form
an alcohol C4H9OH, the rate of reaction is found to be unaffected by changes in the concentration
of OH– ions present.
Which is the most likely molecular structure of Y?
A CH3CH2CH2CH2Br
B CH3CH2CHBrCH3
C (CH3)2CHCH2Br
D (CH3)3CBr
Pls solve dis

if rate in unaffected by concentration of OH it means that the slow step doesn't involve OH. it means it is Sn1 reaction. so the bromine is on a teriary carbon.so D is the answer.

 

[Suchal Riaz]

but i was talking about the water and ethyl ethanoate... it means when there is no units we can take 1?

the moles of water are not = 1
the moles of water and ethylethanoate = x
the moles of ethanol and ethanoic acid were 1 initially
so the moles of them must be 1-x because x moles were used up to make water and ethylethanoate. read the diagram again. expecially the table.

 

[ZaqZainab]

but i was talking about the water and ethyl ethanoate... it means when there is no units we can take 1?

here i did a little editing i hope suchal doesn't mind

 

[Suchal Riaz]

View attachment 45161
here i did a little editing i hope suchal doesn't mind

OH F**K i wrote 1 instead of x sorry.

 

[♣♠ Magnanimous ♣♠]

thanks ZaqZainab and Suchal Riaz

 

[Suchal Riaz]

i solved it on the paper and then copied on the mspaint but i made a typo. sorry

 

[Metanoia]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_11.pdf

Q4(C),17(C),20(C),27(D),35(B),36(A)

w11qp11

Q4. There is 1 lone pair on the N atom. So we have 2 bond pairs and 1 lone pair, which is sightly below 120 degrees.

Q17. Volatility has to do with intermolecular attraction. As electrons/protons increases, the instantaneous dipole- induced dipole gets stronger.

Q20. Cold dilute Mno4 adds 2 OH across the double bond. Hot MnO4 cleaves the double bond, and there are 2 6-member rings left.

Q27. CH3CH2CH2CH3
Replacing any the 6 red H gives us 1-chloropropane
Replacing any of the 4 white H gives us 2-chloropropane.
So by probability, we have 6:4 which is 3:2

Q35:
Cl- --> HCl (no redox)
Br- --> HBr --> Br2 (oxidised)
I- --> HI --> I2 (oxidised)

Q36.
X is N2 (alkaline hydride is NH3)
Y is NO (diatomic)
Z is NO2 (polar)

 

[♣♠ Magnanimous ♣♠]

i solved it on the paper and then copied on the mspaint but i made a typo. sorry

telling to whom bro?

 

[princessnoor]

In statement 1, 2 moles of ethanoic acid will react with 1 mole of calcium ion as charge on calcium is +2. So compound will be Ca(CH3CO2)2 which has empirical formula CaC4H6O4.
In 2 and 3, both H from CO2H will be removed so empirical formula will be CaC4H4O4 and not CaC4H6O4.

Also i dont get Qs 11 and 23 in this ppr http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_13.pdf

 

[Ahmed Aqdam]

The answer would be C we can have CH3●
we can have CH3CH2●
or just CH●

How CH●? If you remove from the methyl groups they will be same but not CH.

 

[princessnoor]

In statement 1, 2 moles of ethanoic acid will react with 1 mole of calcium ion as charge on calcium is +2. So compound will be Ca(CH3CO2)2 which has empirical formula CaC4H6O4.
In 2 and 3, both H from CO2H will be removed so empirical formula will be CaC4H4O4 and not CaC4H6O4.

hey for how long u will b available today cuz i might hve some more questions nd u know tomorow is ppr

 

[ZaqZainab]

How CH●? If you remove from the methyl groups they will be same but not CH.

C● ehhh sorry

 

[Metanoia]

Also i dont get Qs 11 and 23 in this ppr http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_13.pdf

Hi, please include answers to the questions so its easier to reply.

s12qp13

Q11. Unless you can do them mentally, it might be advisable to adopt a trial and error approach to this question.
Go from options A to D and see which one gives you the correct total moles of gases in the end

I will use B as example as its the answer.



Q23. Draw all possible structural isomers of C4H8O2 that has ester bonds.

E.g CH3CH2COOCH3, CH3COOCH2CH2CH3, etc...

 

[umair1161]

1 mole=24 dm^-1
x moles= 0.3 dm^-1 (volume of O2)

This way we will get the moles of oxygen: 0.0125 mol

Then using the mass of each element we find the moles of that particular element using the formula moles=mass÷molecular mass. Then we form equations of the reaction of each element with oxygen:

Ca + 0.5 O2 -> CaO
Mg +0.5 O2 -> MgO
2K + 0.5 O2 -> K2O
2Na + 0.5 O2 -> Na2O

Since we already have the moles of each element, we can now find the moles of oxygen each element requires and that should be equal to 0.0125.

In this case 0.05 moles of sodium gives us 0.0125 moles of O2. Hence the answer D.

Ahh! I get it now! Thanks alot!

 

[Ahmed Aqdam]

Also i dont get Qs 11 and 23 in this ppr http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_13.pdf

11: A: x mol of R, 2 mol of Q so total 3x of products. P is initially x so as 1 mole of P it will be 2-x. Total are 2+2x
B: x mol of R, 2 mol of Q so 2x. P is 2-2x as 2 moles of P. Total are 2+x
C: x mol of both R and Q and P is again 2-2x so total 2 moles.
D: x mol of R, 0.5 mol of Q, P is 2-x as x will be halved here as R is 2 moles. Total 2+0.5x

23: Two with acid Methanoic, one with ethanoic, one with propanoic.
Two with methanoic acid as one straight chain and the other with methyl group.