Chemistry: Post your doubts here!

[ZaqZainab]

questions says that there are one mole of water and ethyl ethanoate.
and when Kc has no units or when the volume of concentration cancel out, moles can be used in the equation.
[a]/[c][d] = (n(a)n(b)/V)/(n(c)n(d)/V) volume will cancel out giving number of moles only.

In the question it doesnt say one mole of water

 

[IGCSE13]

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

 

[Suchal Riaz]

 

[princessnoor]

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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.

thanku

 

[_Ahmad]

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)

 

[Suchal Riaz]

i meant moles of ethanol and ethanoic acid

In the question it doesnt say one mole of water

 

[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