Chemistry: Post your doubts here!

[hmlahori]

http://www.xtremepapers.com/CIE/International A And AS Level/9701 - Chemistry/9701_s07_qp_1.pdf

Q18.

The gas released is ammonia gas(an alkaline gas so pH paper turns blue). So the fertilizer must contain the ammonium ion, means it is ammonium nitrate,(NH4NO3). Rearranging this we get N2H4O3. So the answer is D.

 

[hmlahori]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_12.pdf
Q4

So the balanced equation for the reaction is N2 + 3H2 ==} 2NH3
If 96 kg of H2 was left at equilibrium that means (120-96= 24 kg) 24 kg of H2 reacted.

So according to equation 3 mol of H2 : 2 mol of NH3
6 g : 34 g
0.006 kg : 0.034 kg
24 kg : (24 multiplied by 0.034/0.006)
= 136 kg. answer is C.

 

[Nikesh]

View attachment 7881
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i have a problem in these type of questions where the examiner asks about the possible products of oxidation or reduction.
Please help

the answer is B because its 2nd degree alcohol which gives ketone when oxidised by potassium dichromate

 

[hmlahori]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w03_qp_1.pdf
http://www.xtremepapers.com/papers/...and AS Level/Chemistry (9701)/9701_w03_er.pdf
Q 28?

 

[Mubasher96]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w03_qp_1.pdf
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w03_er.pdf
Q 28?

i didn't get the question myself, but this might help u.
http://www.thestudentroom.co.uk/showthread.php?t=1468494
http://www.xtremepapers.com/community/threads/chem-mcq-help.7935/ post# 5, i.e

"the answer for 28 is B because the compound has three -OH groups so the hydrogens can be easily dispalaced due to the high electronegativity of oxygen."

 

[Soulgamer]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w03_qp_1.pdf
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w03_er.pdf
Q 28?

Take the reaction as:

R(alkyl chain)-O-H +D2O----> R-O-D +HDO.
Its a simple question about substitution.

 

[JD REBORN]

thn

So the balanced equation for the reaction is N2 + 3H2 ==} 2NH3
If 96 kg of H2 was left at equilibrium that means (120-96= 24 kg) 24 kg of H2 reacted.

So according to equation 3 mol of H2 : 2 mol of NH3
6 g : 34 g
0.006 kg : 0.034 kg
24 kg : (24 multiplied by 0.034/0.006)
= 136 kg. answer is C.

thnx very much

 

[DPratik]

october november 2011 paper 12 question 26
help plsssssssssssssssssss

the answer can be found by different ways,there is even a formula to solve this,but I prefer it solving by my calculating...
no of moles of ethanol=2.3/46
=0.05 moles of ethanol
now as the question has stated that the yield of the product was 70% which means 70% of the moles of ethanol was converted into product
i.e...no moles of product form = 70% of 0.05
=0.035 moles of product was formed
The question has mentioned gentle heating which means it is obvious that the product form is ethanal...

Mr 0f ethanal=44
so amount of product form = 44 * 0.035 !!

 

[leosco1995]

Thanks for the explanation guys. If you don't mind, could you explain the following MCQs in this paper: http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w07_qp_1.pdf

Q37: Why isn't 3 right? NDH3Cl should be the same as NH4Cl and to my knowledge, that should liberate NH3. And how is 2 right?
Q30: I'm not getting any of the options here..
Q9 and Q5 as well.

Thanks in advance.

 

[gary221]

Thanks for the explanation guys. If you don't mind, could you explain the following MCQs in this paper: http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w07_qp_1.pdf

Q37: Why isn't 3 right? NDH3Cl should be the same as NH4Cl and to my knowledge, that should liberate NH3. And how is 2 right?
Q30: I'm not getting any of the options here..
Q9 and Q5 as well.

Thanks in advance.

For 5, the ans is A...
Bcoz hydrogen bonding takes place btw polar molecules, n of the 4, methanol ie an alcohol is the most polar...
thus hydrogen bonding will take place wth it

Polarity Ranking of the Functional Groups:
(most polar first)

Amide > Acid > Alcohol > Ketone ~ Aldehyde > Amine > Ester > Ether > Alkane

Hope i helped!

 

[leosco1995]

For 5, the ans is A...
Bcoz hydrogen bonding takes place btw polar molecules, n of the 4, methanol ie an alcohol is the most polar...
thus hydrogen bonding will take place wth it


Hope i helped!

Oh, okay. So if there was no alcohol in one of the options, then the hydrogen bonding with the ketone (option C) because that would be the most polar instead?

 

[gary221]

Oh, okay. So if there was no alcohol in one of the options, then the hydrogen bonding with the ketone (option C) because that would be the most polar instead?

yes

 

[étudiante]

yes

Ketones have hydrogen bonding? i thought dey dont cuz O is not attatched to an electronegative element... can u pls clear my confusion?
thanks in advance

 

[gary221]

Ketones have hydrogen bonding? i thought dey dont cuz O is not attatched to an electronegative element... can u pls clear my confusion?
thanks in advance

well, they r polar, right?? check this out..

The carbonyl group is polar as a consequence of the fact that the electronegativity of the oxygen center is greater than that for carbonyl carbon. Thus, ketones are nucleophilic at oxygen andelectrophilic at carbon. Because the carbonyl group interacts with water by hydrogen bonding, ketones are typically more soluble in water than the related methylene compounds

 

[étudiante]

well, they r polar, right?? check this out..

well... dey are POLAR dat doesn't mean dey have hydrogen bonding.... as far as i understand, hydrogen bonding occurs only in substances where O is attatched to an electonegative element lyk Oxygen...

 

[gary221]

well... dey are POLAR dat doesn't mean dey have hydrogen bonding.... as far as i understand, hydrogen bonding occurs only in substances where O is attatched to an electonegative element lyk Oxygen...

sorry..whr O is attached to oxygen??

 

[étudiante]

sorry..whr O is attached to oxygen??

sorry.... ma bad! i meant H attatched to an electronegative elemnt like O
really sorry!

 

[gary221]

sorry.... ma bad! i meant H attatched to an electronegative elemnt like O
really sorry!

oh...yeah i know tht..but rd this..
The carbonyl group is polar as a consequence of the fact that the electronegativity of the oxygen center is greater than that for carbonyl carbon. Thus, ketones are nucleophilic at oxygen andelectrophilic at carbon. Because the carbonyl group interacts with water by hydrogen bonding, ketones are typically more soluble in water than the related methylene compounds. Ketones are hydrogen-bond acceptors. Ketones are not usually hydrogen-bond donors and cannot hydrogen-bond to itself

 

[gary221]

oh...yeah i know tht..but rd this..
The carbonyl group is polar as a consequence of the fact that the electronegativity of the oxygen center is greater than that for carbonyl carbon. Thus, ketones are nucleophilic at oxygen andelectrophilic at carbon. Because the carbonyl group interacts with water by hydrogen bonding, ketones are typically more soluble in water than the related methylene compounds. Ketones are hydrogen-bond acceptors. Ketones are not usually hydrogen-bond donors and cannot hydrogen-bond to itself

So doesnt ths mean tht although a ketone cnt hydrogen bond wth itself, it can wth othrs??

 

[étudiante]

oh...yeah i know tht..but rd this..
The carbonyl group is polar as a consequence of the fact that the electronegativity of the oxygen center is greater than that for carbonyl carbon. Thus, ketones are nucleophilic at oxygen andelectrophilic at carbon. Because the carbonyl group interacts with water by hydrogen bonding, ketones are typically more soluble in water than the related methylene compounds. Ketones are hydrogen-bond acceptors. Ketones are not usually hydrogen-bond donors and cannot hydrogen-bond to itself

ohkay.... so it can hydrogen bond wid water but not wid itself? is dat ryt?
THANX A LOT! :,)