Chemistry: Post your doubts here!

[saudha]

That's a very good one. Thank you very much.
Do you know some other sites like this where i can obtain more examples and explanations? Thanks again.

let me see if i find one ill post it.......

 

[panda222]

I..want..the..marking..scheme..for..year..2002

Are you talking about Winter 2002 or summer 2002. If winter, then I second this (Only for Paper 1 tho, the rest of them are up there)

Are you by any chance having trouble with the Winter MCQ for 2002? Cuz i am.

 

[smartangel]

this question is from the AS and A level chemistry coursebook..could someone explain why is the answer B?

Which one of the following reactions is accompanied by the largest percentage increase in volume? ​

A 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) ​

B 2NH3(g) → N2(g) + 3H2(g) ​

C CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) ​

D S(s) + O2(g) → SO2(g)

 

[smzimran]

this question is from the AS and A level chemistry coursebook..could someone explain why is the answer B?

Which one of the following reactions is accompanied by the largest percentage increase in volume? ​

A 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) ​

B 2NH3(g) → N2(g) + 3H2(g) ​

C CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) ​

D S(s) + O2(g) → SO2(g)

AoA,
A:
9 moles of gas produce 10 moles of gas, so % increase is:
= (10 - 9 / 9) * 100% = 11.1%

B:
2 moles produce 4 moles, so % increase is:
= (4 - 2 / 2) * 100% = 100%

C:
3 produce 3, so % increase is:
= (3-3 / 3) * 100 = 0%

D:
1 moles of gas produce 1 mole, so % increase is:
= (1 - 1 / 1) * 100 = 0%

Thats why the answer is B

 

[CaptainDanger]

9701_s09_qp_1.pdf
9701_s09_ms_1.pdf

MCQ 28, 29 & 30?

 

[Rabib_69]

Can anyone help me with M/J 11 52, the first question? Just sort of briefly describe the procedure to me?

 

[MEGUSTA_xD]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w08_qp_1.pdf Q29

 

[smartangel]

okay i really need help with these questions.. 1,4,8,15,16,25,26,29,36.. in some of them i do have an explanation for my answer but apparently they:re wrong so if someone could please correct me!
in 16 isnt the major product of the electrolysis of brine, NaOH?
1n 25 (2.76 - 2.07)/2.76 x 100 gives us 75%. so why isnt B the answer?
in 29..why cant C be the right answer? im getting 3 Ch3 and 3 Ch2..
in 36..if we consider S then it doesnt form a basic hydride?

i know these are quite a lot of questions but please do help me out! thanks!

 

[USMAN Sheikh]

Help needed as soon as possible plsssssss be quick in correcty reply !!! Do explain me the following questions pls 11 16 22 23 40 pls uickly JAZAKALLAH !!

 

[rockerzregmi]

Application help .. revision plz urgent

 

[USMAN Sheikh]

THIS ONE TOO PLSSSS ques no 2 and 5 only plsssssss be quick (((

 

[Amy Bloom]

let me see if i find one ill post it.......

Thanks ^^

 

[HM.RABBI]

Help me with this man

http://www.xtremepapers.com/community/threads/chemistry-a-lvl-moles-problem.13529/

 

[Amaryllis]

hi everyone

i have some questions that are confusing me
Q21-q10- in http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s06_qp_1.pdf
and also Q29 why its B
i think that both aldehydes and ketones can be reduced by NABH4 ...aldehydes into primary alcohols and ketones into secondary?

can anybody help me in identifying the chiral centers too..im getting confused from these ..if somebody have some notes for them or somthing
i will really appreciate that

 

[hm12]

yes both aldehyde and ketones can be reduced by NABH4 but the questions says which of them reacts with both NABH4 and tollens reagent so only aldehydes react with both of them ketones dont react with tollens reagent so the answer is B

 

[amatyasrizan]

How to approach this question?Detailed method please..

 

[hassam]

what type of bond is formed b/w the drug and dna

 

[HM.RABBI]

what type of bond is formed b/w the drug and dna

Firstly it forms covalent bond ......The Cl attracted to the hydrogen and so a covalent bond is formed with HCl as byproduct

 

[HM.RABBI]

I have a problem with 9701/43/o/n/10 q no . 5

Why in (b -i ) the 1.23 is positive ???? I should be -ve shouldn't it be E= -1.23-(-.83)

Why in (b -i ) the 1.23 is positive ???? I should be -ve shouldn't it be E= -1.23-(-.83)

Then in (c-i) why less positive and how it affect the (C- ii)

 

[HM.RABBI]

Can anyone give me the list of the bond angles in our syllabus ????????