Chemistry: Post your doubts here!

[AbbbbY]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s13_qp_13.pdf
explain Q38 please

D!

When tackling Section B, always look at 2 first. If 2 is wrong, it has to be D.

If it forms Hydrogen Bonds readily, it's soluble. If it's soluble, it makes no sense as to why it's present. So, I'd go with D.

 

[Youssef Tawil]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_11.pdf
Number 40 , answer is D
why is 2nd statement incorrect?

 

[Ahmed Aqdam]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_11.pdf
Number 40 , answer is D
why is 2nd statement incorrect?

Reaction of bromoethane with aqueous ammonia requires heating and does not occur at room temperature.

 

[Browny]

Can somebody please explain the following questions?

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_12.pdf

Question 13 ans C.

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf

Question 14 ans B.

 

[NIM]

1)Mass - 0.216g
no. of moles = 0.216/108 = 2x10^-3
1 mol = 6.03x10^23 atoms
so 2x10^-3 mol = (6.03x10^23) x (2x10^-3) atoms
= 8.0 x 10 ^18

40) the answer is C because the two top and bottom groups are the same so statement 1 is wrong and since statement one is wrong, C has to be right. you can check statements two and three for satisfaction.

thnx
its not 40 its 4
cn u plz help me wid 4, 30, 33

 

[NIM]

Hi there, I tried the questions. I was unable to find a solution to question 30.
otherwise, in question 5, you have to halve both the enthalpy changes given and then add them because by definition enthalpy change of formation is only for one mole of a substance and in order to make I2, the enthalpy change of the second reaction is necessary.


ques 15 - only chlorides give colourless solution with excess dilute ammonia.

ques 24 - the answer is B because during hydrolysis the ester bond is broken and the part that comes from the alcohol becomes the alcohol again (inbox me if you still don't get it).

yeah thnx i got it bt cn u plz xplain 35 and 39 also
thnx a lot

 

[Metanoia]

Can somebody please explain the following questions?

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_12.pdf

Question 13 ans C.

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_12.pdf

Question 14 ans B.

w11qp12

Q13.
C burning in excess O2 forms CO2
S burning in excess O2 forms SO2, some amounts of SO3 might be formed, but would be a minor product compared to SO2.
H burning in excess O2 forms H2O

s12q12

Q14
CaCO3--> CaO + CO2 (Thermal decomposition, takes in energy, endothermic)
CaO + H2O --> Ca(OH)2 (hydration of lime, exothermic)

 

[Zepudee]

Can anyone help me with his?

 

[Zepudee]

And this? Anyone?

 

[Zepudee]

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

Q11,17, and 23!

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s13_qp_12.pdf
Q3 and 40!

 

[Zepudee]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s08_qp_1.pdf

Q6,26 and 27!

 

[Metanoia]

thnx
its not 40 its 4
cn u plz help me wid 4, 30, 33

w07pq1

Q4. There is a significant increased in IE from removing the 2nd to the 3rd electron, means the atom has two outer electrons.

Q30. From CH3CH2CH2CO2CH3, the acid produced upon hydrolysis is CH3CH2CH2COOH .
Chemical formula is C4H8O2, empirical formula (simplest ratio) C2H4O

Q33.
Statement 1: (False) The gas is exerting the same pressure as the atmosphere outside, otherwise the plunger will either move left or right.
Statement 2: (True) When plunger moves inwards, it causes the pressure to increase, the eqm will shift to the left to reduce pressure (produce less moles of gas).
Statement 3: (True) For every one mole of PCl5 dissociated, two moles of gases were formed (1 mol of PCl3 and 1 mol of Cl2). So total volume of gases after dissociation is more than original volume of gas without dissociation.

 

[Metanoia]

yeah thnx i got it bt cn u plz xplain 35 and 39 also
thnx a lot

s10qp12

Q35.
X could be NO or SO2.
NO + 1/2O2 --> NO2
SO2 + 1/2 O2 --> SO2
Based on examiners report, they don't view CO reacting with O2 as natural reaction with atmosphere, instead it requires burning.

Q39. Hmm Q39, it depends if you are able to draw out the structure and use the rules of naming branched alkanes. You can post your structures after drawing for us to check what is the problem...

 

[Metanoia]

Can anyone help me with his?

This looks familar, I believed I might have explained it in one of the videos.

Maybe you could check the year of paper and see if it was indeed one of those I upload.

 

[Metanoia]

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

Q11,17, and 23!

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s13_qp_12.pdf
Q3 and 40!

Please include the answers so its easier to reply with our suggestions.

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

Q17. Conc H2SO4 can donate a proton to CH3CH2OH to form CH3CH2OH2+
Conc H2SO4 can dehydrate ethanol to ethene.

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


June 2013 P12, I covered in the videos, so will avoid typing again...but if the explanations in video don't make sense, feel free to clarify.

 

[Metanoia]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s08_qp_1.pdf

Q6,26 and 27!

s08qp1

Q6.
H2O(s) --> H2O(g)

Moles of H2O = mass of ice/Mr of H2O = 1/18= 0.0556

PV/nT (ideal gas) = PV/nT (H2O)
(1)(24)/(1)(298) = (1)V/(0.0556)(596)

V = 2.67 dm^3

Q26.
Increase in the 2 oxygen means that the 2 OH has been oxidized to 2 COOH groups.
The two OH must be primary alcohols. Since is an unbranched butanol, the OH groups are on carbon 1 and 4.

Q27.
Use the 4 options and trial and error.

Before dehydration, the C=C bonds were actually CH-COH.

Check which of the 4 could possibly give us a tertiary alcohol (resistant to oxidation) before dehydration.
View attachment 44341
In this case, it was D.

 

[kruti]

Hi guys,
Please help out with the following questions:
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w09_qp_12.pdf

Question 12 ans. C
Question 20 ans. A

 

[forever_chocoholic]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_12.pdf
Q: 40

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_12.pdf
Q: 24

can anyone explain these questions pleaseeeee!

 

[Sameer556]

Use of the Data Booklet is relevant to this question.
In the gas phase, aluminium and a transition element require the same amount of energy to form
one mole of an ion with a 2+ charge.
What is the transition element?
A Co
B Cr
C Cu
D Ni

 

[Abdul Basit]

Q6 guys