Chemistry: Post your doubts here!

[Metanoia]

Can you please explain further more for the Q27? Can you also please draw (CH3)3CCH2OH? I thought it is a tertiary alcohol? And why is it resistant to dehydration but not the second one? Sorry! But Thank you so so much! Next time I will include answers in it

Hmm...perhaps you try drawing out the 2 alcohols, so I can check how you visualise the structures.

 

[Snowysangel]

Guys i need ur help in this
Q2 and 13 are done

Electronegativity increases down a period and up a group because the effective nuclear charge is the greatest. Sulfuric acid usually acts as an acid but acts as an oxidizing agent when it itself gets reduced into sulfur, sulfurdioxide or hydrogen sulfide. HI and HBr ate strong enough reducing agents to reduce sulfuric acid

 

[_Ahmad]

please help

Q16,24,27,34 of http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_13.pdf

 

[GCE As and a level]

Metanoia , ZaqZainab ,@ EVERY ONE
Plz guys i need help in these
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w05_qp_1.pdf
Q3...Answer B>>>I cant understand the question :s
Q12..Answer D>>>Shouldnt the answer be B ,cuz for Mg--> Mg+0.5 O2=MgO
for Al --> 2Al+1.5 O2=Al2O3
for S --> S+O2 = So2
Q17..Answer B>>>I cant understand a single word
Q18..Answer C
Q20..Answer B>>>Should i include the Structural isomer also ?
Q24..Answer C
Q30..Answer B
Q31..Answer A>>>Wat the exactly want??
Q33..Answer A>>> How could i know that 2 and 3 are also correct
Q34..Answer B

Q_IS there any way that could help me to know if the reaction is Electrophillic or Nucleophillic??
THNX GUYS

 

[Metanoia]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_12.pdf

Can anybody please explain question 11 ans C, 23 ans B, 32 ans D?

s11qp12

short answer, cross the Al3+ and C4- charges, though it might not always work.

Long answer
Understand that whatever moles of C we have at the beginning will eventually be the same number of moles of C in CO2 at the end.

Let x and y be the ratio of Al and C respectively.
AlxCy --->???---> CO2

Working backwards from CO2,
moles of CO2 = 72/24 000 = 0.003 moles = moles of C in AlxCy

Going through the options
A Al 2C3, moles of Al2C3 = 0.144/90 = 0.0016, moles of C = 0.0016 x 3 = 0.0048 (incorrect)
B Al 3C4 , moles of Al3C4 = 0.144/129 = 0.0016, moles of C = 0.0016 x 4 = 0.0045 (incorrect)
C Al 4C3 , moles of Al4C3 = 0.144/144 = 0.001, moles of C = 0.001 x 3 = 0.003 (BINGO!)
D Al 5C3

Q23.

CxHy --> CH4 + 2C2H4 + C3H6
x = 8, H=18

Q32. If gas was ideal, it volume would decrease by 4 times (76 to 19cm^3) when pressure was increased by four times.
However, its volume decreased to 25 cm^3 instead. It just means it does not follow ideal gas law, i.e. not ideal.

 

[GCE As and a level]

Electronegativity increases down a period and up a group because the effective nuclear charge is the greatest. Sulfuric acid usually acts as an acid but acts as an oxidizing agent when it itself gets reduced into sulfur, sulfurdioxide or hydrogen sulfide. HI and HBr ate strong enough reducing agents to reduce sulfuric acid

Thanks

 

[Metanoia]

Guys, please don't keep copying and pasting your questions. Its very hard to keep track.

If there are questions you already understood while waiting, its better to update your original posts.

Be patient.

 

[GCE As and a level]

Guys, please don't keep copying and pasting your questions. Its very hard to keep track.

If there are questions you already understood while waiting, its better to update your original posts.

Be patient.

Guys, please don't keep copying and pasting your questions. Its very hard to keep track.

If there are questions you already understood while waiting, its better to update your original posts.

Be patient.

Is this for me ???!
Ur answering all the doubts except mine ............ As if we are enemies

 

[♣♠ Magnanimous ♣♠]

Is this for me ???!
Ur answering all the doubts except mine ............ As if we are enemies

lol

 

[Metanoia]

Is this for me ???!
Ur answering all the doubts except mine ............ As if we are enemies

This is for everyone who is doing so. I'm sorry that you have the idea that I have not answered any of your doubts.

 

[GCE As and a level]

This is for everyone who is doing so. I'm sorry that you have the idea that I have not answered any of your doubts.

No man
NVM
IK this
I am just joking
DONT take it seriously
.............But i am still waiting my doubts to get solved

 

[Snowysangel]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_13.pdf 12(C)

 

[Snowysangel]

s11qp12

short answer, cross the Al3+ and C4- charges, though it might not always work.

Long answer
Understand that whatever moles of C we have at the beginning will eventually be the same number of moles of C in CO2 at the end.

Let x and y be the ratio of Al and C respectively.
AlxCy --->???---> CO2

Working backwards from CO2,
moles of CO2 = 72/24 000 = 0.003 moles = moles of C in AlxCy

Going through the options
A Al 2C3, moles of Al2C3 = 0.144/90 = 0.0016, moles of C = 0.0016 x 3 = 0.0048 (incorrect)
B Al 3C4 , moles of Al3C4 = 0.144/129 = 0.0016, moles of C = 0.0016 x 4 = 0.0045 (incorrect)
C Al 4C3 , moles of Al4C3 = 0.144/144 = 0.001, moles of C = 0.001 x 3 = 0.003 (BINGO!)
D Al 5C3

Q23.

CxHy --> CH4 + 2C2H4 + C3H6
x = 8, H=18

Q32. If gas was ideal, it volume would decrease by 4 times (76 to 19cm^3) when pressure was increased by four times.
However, its volume decreased to 25 cm^3 instead. It just means it does not follow ideal gas law, i.e. not ideal.

In q32, does the gas partially turn into a liquid too?

 

[Zepudee]

Can someone please look into these difficult questions?

View attachment 45028


View attachment 45029


View attachment 45030

FOR Q11

s11qp12

Q11.
Some students have suggested using Al3+ and "crossing it" with C4- to get Al4C3

The "crossing of charges method" does give us the correct answer in this case, so if all else fails, I guess we can use it. However, lets see if we can make us of the other information given.

Understand that whatever moles of C we have at the beginning will eventually be the same number of moles of C in CO2 at the end.

Let x and y be the ratio of Al and C respectively.
AlxCy --->???---> CO2

Working backwards from CO2,
moles of CO2 = 72/24 000 = 0.003 moles = moles of C in AlxCy

Going through the options
A Al 2C3, moles of Al2C3 = 0.144/90 = 0.0016, moles of C = 0.0016 x 3 = 0.0048 (incorrect)
B Al 3C4 , moles of Al3C4 = 0.144/129 = 0.0016, moles of C = 0.0016 x 4 = 0.0045 (incorrect)
C Al 4C3 , moles of Al4C3 = 0.144/144 = 0.001, moles of C = 0.001 x 3 = 0.003 (BINGO!)
D Al 5C3

Q23.
To be honest, I feel that the wording in this question is a bit imprecise and can be misinterpreted.
Using the most straightforward interpretation:
CH4 : C2H4: C3H6
1: 2 : 1
Adding up the C and H, we have C8H18

from Metanoia

 

[Metanoia]

explain followingView attachment 45018 View attachment 45019

Q14.
Group II nitrates decompose based on the equation below:

2 X(NO3)2 (s) --> 2 XO (s) + 4 NO2 (g) +O2(g)

Mass of XO = 1.47 g
Moles of XO = 1.47/ (Mr of X + 16)

Mass of X(NO3)2 = 3 g
Moles of X(NO3)2 = 3/(Mr of X + 124)

since moles of X(NO3)2 = moles of XO
3/(Mr of X + 124) = 1.47/ (Mr of X + 16)

Solve for Mr of X.

Q10
Heat of neutralization for strong acids and strong alkali is estimated to be -57kJ PER MOLE of H2O formed.

For both experiments. (Involving strong acid and bases) , it reflects twos moles of water formed .

So heat of reaction is -57 x 2 for both equations.

 

[Metanoia]

Question 20 please...

Q2o. IF all carbons are single bonds, CnH2n+2O, C20H42O (20 carbons , 42 hydrogen, 1 oxygen)

Since 1 aldehyde group is present, subtract 2 H, C20H40O (20 carbons , 40 hydrogen, 1 oxygen)

Since it contains a ring, subtract another 2H, C20H38O (20 carbons , 38 hydrogen, 1 oxygen)

Since retinal contains only 28 H, the missing 1o H are due to 5 double bonds.

 

[Metanoia]

Q31 : is it PH3 is trigonal planar ? i though it should be trigonal pyramidal ???

PH3 should be trigonal pyramidal.

 

[ZaqZainab]

yes please!

 

[Metanoia]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s13_qp_11.pdf

Help in q30 please. Cant differentiate between B and D.

Focus on the H atoms across the C=C bonds.
B is trans and D is cis isomer.

 

[Metanoia]

Is carboxylic acid completely soluble in water?

The smaller ones are soluble, but as the alkyl length gets longer (more than 5 C) it gets less soluble.