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Chemistry: Post your doubts here!

B

Browny

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Metanoia

Metanoia

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GCE As and a level said:
Hey guys
could u plz help me with this :s
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_11.pdf

DOUBTS:

Q2 ----> ANSWER D

Q3 ----> ANSWER D

Q9 ----> ANSWER B

Metanoia
Click to expand...

s12qp11

Q2. Removing products shift the equilibrium to the right, but does not increase the forward rate of reaction. Please see post #9494 for a sketch explanation.

Q3. Equation can represent both
Heat of formation of water : H2 (g) + 1/2 O2 (g) --> H2O (l) , exothermic
or heat of combustion of H2

Q9. Please check post 9224 on pg 462

FInally, perhaps a simple request to students posting questions here, besides including the answers, it would be more productive to also write down which part of the questions or which of the suggested options you don't understand or agree with. Then it allows those who intend to help to check your understanding.

Something like what browny did here. :)
Browny said:
...

The problems are as follows:

In 5 why can't A be correct as it is symmetrical.
In 13 why can't A(Mg) be the answer as when it dissolves the pH is around 6.5 which suggests hydrolysis.
In 23 why can't D(180) be the answer as the chain is like -C-C-C-C-C- which shows the C-C-C bond to be 180.
In 36 why is 2(NH3 behaves as a base) is correct.
In 39, actually I don't get a single point!

Thanks in advance and please try these questions out if possible as they are confusing and they might even help you out!
Click to expand...
 
GCE As and a level

GCE As and a level

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Metanoia said:
s12qp11

Q2. Removing products shift the equilibrium to the right, but does not increase the forward rate of reaction. Please see post #9494 for a sketch explanation.

Q3. Equation can represent both
Heat of formation of water : H2 (g) + 1/2 O2 (g) --> H2O (l) , exothermic
or heat of combustion of H2

Q9. Please check post 9224 on pg 462

FInally, perhaps a simple request to students posting questions here, besides including the answers, it would be more productive to also write down which part of the questions or which of the suggested options you don't understand or agree with. Then it allows those who intend to help to check your understanding.

Something like what browny did here. :)
Click to expand...
Thnx
but in my doubts i didnt understand a single word of question :p
and i cant chech the 477 pages to search for my doubt :p
THANK YOU!!!!
 
Metanoia

Metanoia

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Browny said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w04_qp_1.pdf

Can anybody please explain question 5 ans B, 9 ans B, 12 ans B, 18 ans C, 20 ans A, 38 ans A, please?

Some other problems are in question 11 why can't B be correct, 30 how to draw A and in 31 if a reaction is like from A to B and the energy change is +20 then if the reaction is from B to A is the change -20?:)
Click to expand...


W04qp1

Q5. You have to imagine yourself filling up the boxes with 8 electrons. If you follow the rules, you will end up with a final configuration that has the lowest energy level.

Q9. The short answer is, compared other organic compounds with the same number of carbons, burning a hydrocarbon usually gives use the most energy.
The C-O bonds for the rest require a bit more energy to break, compared to one that has only C-H single bonds.

Q11. No change in oxidation states for any atom, cant be redox reaction.

Q12. A boltzman distribution curve for a higher temperature with have its peak shifted to the right, and in a lower height.

Q18. For all the other options, there are dative bonds formed from nitrogen's lone pair.
A. N: -->C
B. N: -->H+
D. N: --> Ag+

Q38.

Y reflects the idea that ppt is formed faster than CH3CH2Cl which gives off 1 Cl- to precipitate with Ag+
1. Formed faster as it gives of 2 Cl-
2. Formed faster as C-Br bond is weaker, so Br- is released faster
3. Formed faster as C-I bond is weaker, so I- is released faster
 
B

Browny

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Metanoia said:
W04qp1

Q5. You have to imagine yourself filling up the boxes with 8 electrons. If you follow the rules, you will end up with a final configuration that has the lowest energy level.

Q9. The short answer is, compared other organic compounds with the same number of carbons, burning a hydrocarbon usually gives use the most energy.
The C-O bonds for the rest require a bit more energy to break, compared to one that has only C-H single bonds.

Q11. No change in oxidation states for any atom, cant be redox reaction.

Q12. A boltzman distribution curve for a higher temperature with have its peak shifted to the right, and in a lower height.

Q18. For all the other options, there are dative bonds formed from nitrogen's lone pair.
A. N: -->C
B. N: -->H+
D. N: --> Ag+

Q38.

Y reflects the idea that ppt is formed faster than CH3CH2Cl which gives off 1 Cl- to precipitate with Ag+
1. Formed faster as it gives of 2 Cl-
2. Formed faster as C-Br bond is weaker, so Br- is released faster
3. Formed faster as C-I bond is weaker, so I- is released faster
Click to expand...

Thanks so much for the help, I just coudn't figure out thee questions !!!(y)(y)(y)

But in 11 isn't the Cr oxidation number changed.
And in 12 there are others with the curve shifted and with a lower maximum like D for example.
And in 18 how can we know the structure of the compunds such as in D, beacause I think structure of that is not in our syllabus.
 
Metanoia

Metanoia

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_Ahmad said:
Can anyone PLEASE explain these question!



Q5,7,17,18,24,25,30,33,34 from
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w05_qp_1.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w05_ms_1.pdf
Click to expand...

Princess Raven said:
I could answer 5,6,25,30,33 if u figure out the rest plz tell me how to solve them as well!
Click to expand...

W05qp1

Q17. This question comes from the chapter of transition metals, I'm not sure its relevant to your syllabus now.

Q18. ammonium salt + base --> salt + water + NH3
ammonium sulfate + calcium hydroxide --> calcium sulfate + H2O + NH3
Nutrient of nitrogen in the fertilzer is lost as NH3 gas.

Q24. Three possible alkenes
cis -but-2-ene, trans-but-2-ene and but-1-ene
 
Metanoia

Metanoia

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Browny said:
Thanks so much for the help, I just coudn't figure out thee questions !!!(y)(y)(y)

But in 11 isn't the Cr oxidation number changed.
And in 12 there are others with the curve shifted and with a lower maximum like D for example.
And in 18 how can we know the structure of the compunds such as in D, beacause I think structure of that is not in our syllabus.
Click to expand...

Q11. The Cr is +6 before and after reaction.

Q12. Quite true, its was puzzling to me, the peak if shifted so far right would be really really low. So I prefer the other option. Its debatable.

Q18. That option is under transition metals, I believe is not required in your syllabus.
 
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