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Chemistry: Post your doubts here!

Metanoia

Metanoia

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Browny said:
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.

:)(y)
Click to expand...

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)
 
Metanoia

Metanoia

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NIM said:
thnx
its not 40 its 4 :p
cn u plz help me wid 4, 30, 33 :D
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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.
 
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Metanoia

Metanoia

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NIM said:
yeah thnx i got it bt cn u plz xplain 35 and 39 also
thnx a lot :p
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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...
 
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Zepudee said:
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!
Click to expand...

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

Q6,26 and 27! :)
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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.
 
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Sameer556

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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
 
A

Ahmed Aqdam

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Metanoia

Metanoia

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

Question 12 ans. C
Question 20 ans. A
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w09qp12

Q12. SiCl4 + 2H2O --> SiO2 + 4HCl (acidic)

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.
 
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Metanoia

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forever_chocoholic said:
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! :(
Click to expand...

w09qp12

Q40. Requires a bit of reasoning, if 1 mole of monomer join together, we will get less than 1 mole of polymer.
If we end up with 1 mole of polymer in the end, it means none of the monomer has joined to any other!

Its like 1000 bricks (monomer) will build one house (polymer) , the number of monomer is expected to be more than polymers.
Hope it makes sense.

Q24. The examiner report is pretty lengthy, you can take a read of it. Another way I visualized it that so long as we get smaller molecules than the original, they are more or less feasible.
 
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kruti

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Metanoia said:
w09qp12

Q12. SiCl4 + 2H2O --> SiO2 + 4HCl (acidic)

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

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

Since retinal contains only 28 H, the missing 12 H are due to 6 double bonds.
Click to expand...
Hi,
I do not understand why there will be 42 hydrogen atoms in the first place. The rest of it makes a lot of sense. Thank you. :)
 
Metanoia

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Sameer556 said:
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
Click to expand...

I don't have the data booklet, but perhaps can try adding up 1st and 2nd IE of Al.
Then see which of the options 1st IE + 2nd IE gives the same value.
 
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