Chemistry: Post your doubts here!

[princess Anu]

Why is it A? :S ethane nitrile hydrolysis will make propanoic acid not ethanoic :s

 

[The Sarcastic Retard]

Omg, wth is this? -_-

Correct answer is D.

Use trial and error method.
Take any random Hydrocarbon, let say C2H6 for instance (Try yourself with any hydrocarbon you want to).
A) C2H6 + 5O2 ---> 2CO2 + 3H2O (Not balanced).
B) C2H6 + 7/2O2 ---> 2CO2 + 6H2O (Not balanced).
C) C2H6 + 7/2O2 ---> 2CO2 + 3/2H2O (Not balanced).
D) C2H6 + 7/2O2 ---> 2CO2 + 3H2O (balanced).

 

[The Sarcastic Retard]

oxidant is the one that gets reduced itself right?

Yes.

 

[princess Anu]

28: why A is wrong? if I flip one of the cyclohexenes I think we can get both A nd B :?
29: can somebody make me the isomers.? ans is D :s

 

[The Sarcastic Retard]

Why is it A? :S ethane nitrile hydrolysis will make propanoic acid not ethanoic :s

Ethanenitrile and hydrochloric acid you would get ethanoic acid and ammonium chloride.
CH3CN + 2H2O + HCl ---> CH3COOH + NH4Cl
Ref:
Acidic hydrolysis of nitriles
http://www.chemguide.co.uk/organicprops/nitriles/hydrolysis.html

 

[princess Anu]

http://maxpapers.com/wp-content/uploads/2012/11/9701_w14_qp_13.pdf
Q25
Ans is C but I got only 6 isomers. Can somebody tell me which ones am I missing?

 

[The Sarcastic Retard]

28: why A is wrong? if I flip one of the cyclohexenes I think we can get both A nd B :?
29: can somebody make me the isomers.? ans is D :s

Here :

 

[qwertypoiu]

http://maxpapers.com/wp-content/uploads/2012/11/9701_w14_qp_13.pdf
Q25
Ans is C but I got only 6 isomers. Can somebody tell me which ones am I missing?

There are three double bonds. Each can have Cis or trans. Here are the possibilities:
C...C...C...
C...C...T...
C...T...C...
C...T...T...
T...C...C...
T...C...T...
T...T...C...
T...T...T...

Where T represents a trans and C a cis bond arrangement.

In general, if there are x number of double bonds capable of making cis -trans isomerism (each), there will be a total of 2^x geometrical isomers of that compound.

 

[nehaoscar]

Why is it A?

 

[nehaoscar]

I'm getting B ... NaClO will be formed right?
But then how is it A?

 

[nehaoscar]

Why can it not be C?
Alcohols don't react with Na metal either right?

 

[Mathemagical]

View attachment 54214

I'm getting B ... NaClO will be formed right?
But then how is it A?

6NaOH + 3Cl2 --> 5NaCl + NaClO3+3H2O

The mole ratio of Cl2:NaClO3 is 3:1, so 0.6/3=0.2 mol of NaClO3 will be formed.
Mr of NaClO3 = 106.5
Mass = 0.2*106.5 = 21.3g

Remember, NaClO is only formed with cold sodium hydroxide solution

 

[Mathemagical]

View attachment 54215
Why can it not be C?
Alcohols don't react with Na metal either right?

Alcohols react with sodium metal to form a salt and hydrogen.
For more information visit: http://tinyurl.com/bawcd94

 

[Mathemagical]

View attachment 54212

Why is it A?

This is a tricky one, but it can be done by elimination. B, C and D suggest that the compound may be MgCl2, PCl5 or NaCl.
However, the reactions of the above with water are as such:

MgCl2 + 6H2O --> 2Cl- + [Mg(H2O)6]2+ ; pH 6.7
PCl5 + 4H2o -->H3PO4 + 5HCl ; pH 2
NaCl + H2O --> Na+ + Cl- +H2O ; pH 7

As we can see, none of these fit the information which states that the pH in solution is 12, so Option A is correct.

 

[Abdul Hanan]

27 and 22 are C
29 is D
Thanks for explaining
27 VVVV

 

[Mathemagical]

View attachment 54220 View attachment 54221
27 and 22 are C
29 is D
Thanks for explaining

Question 22:

After polymerising the alkenes they become saturated and so they will not undergo reactions such as hydration and oxidation. Therefore, the answer is C.

Question 27:

Options A and B are incorrect because they do not have CH2CO2CH3 parts in their compounds.
Option D is also incorrect because the left side of the compound shows a carbon atom combined to two other carbon atoms, thus unable to form a double bond with O and a single bond with H which represents an aldehyde group.

 

[Mathemagical]

Question 29:

With the addition of cold dilute KMnO4, two alcohol groups will be added to the carbon-carbon double bond which will in turn form a single bond, hence creating 2 new chiral carbons.

The addition of hot concentrated KMnO4 will oxidise the secondary alcohol group on the left to a ketone, which causes that carbon atom to no longer be chiral.

 

[Abdul Hanan]

Question 22:

After polymerising the alkenes they become saturated and so they will not undergo reactions such as hydration and oxidation. Therefore, the answer is C.

Question 27:

Options A and B are incorrect because they do not have CH2CO2CH3 parts in their compounds.
Option D is also incorrect because the left side of the compound shows a carbon atom combined to two other carbon atoms, thus unable to form a double bond with O and a single bond with H which represents an aldehyde group.

Question 29:

With the addition of cold dilute KMnO4, two alcohol groups will be added to the carbon-carbon double bond which will in turn form a single bond, hence creating 2 new chiral carbons.

The addition of hot concentrated KMnO4 will oxidise the secondary alcohol group on the left to a ketone, which causes that carbon atom to no longer be chiral.

Thanks i do understand 27 and 29 now but can you please explain 22 a bit more? thanks again

 

[princess Anu]

http://maxpapers.com/wp-content/uploads/2012/11/9701_w14_qp_13.pdf

Q29 ( ans is B)
30 (C) nd 20 (C) pleasee

 

[nehaoscar]

Thanks i do understand 27 and 29 now but can you please explain 22 a bit more? thanks again

A - polymerizing will form an alkane. Hydrolyzing alkanes will give CO2 and H2O. so A is wrong

B - polymerizing will form an alkane. KMnO4 reacts with alkenes not alkanes to form alcohols. so B is wrong.

D - same as B; KMnO4 reacts with alkenes not alkanes to form alcohols. so D is wrong

C - polymerizing will form a chloro-alkane (there will be Cl in place of the OH groups)
Hydrolysis will replace the Cl with OH as HCl will be formed.