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Chemistry: Post your doubts here!

M

Metallic9896

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3 guys from my batch said 2015 Paper 12 is hard and they got 27-28 ish, give it a shot. I'll give it a try too.
 
SohaibButt

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ANYONE?
 

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M

Metallic9896

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SohaibButt said:
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Click to expand...

1. It's B cause when the HBr is eliminated and C=C forms, the second C (the one which had the Br) can either form a C=C with the C to its left (the first C), OR form a C=C with the C to its right (i.e., C=C between 2nd and 3rd C). This is 2 structural isomers. Then for the C=C in the middle formed by the 2nd and 3rd C, there will be cis-trans isomerism. So total, 3 isomers. It's not the case in any other option.
 
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Metallic9896

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SohaibButt said:
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Click to expand...

2. Both exist as solid lattice. You should know that I2 is a solid molecular lattice, google it. But you can also get A by eliminating the other incorrect options. It can't be B cause SiO2 is a giant molecular structure, not simple. It can't be C cause CO2 has double bonds. It can't be D cause SiO2 doesn't sublime at room temp. at all as it has a very high melting point and it'd go liquid before going gas. So only A is left which must be true.
 
D

darks

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Any tips for structural isomers etc?
for cis trans... "2^no of double bonds"
for optical... "2^no of chiral carbons"
for stereoisomers... "2^no of chiral carbons+double bonds"
The double bonds are of of course cis trans C=C only.
 
M

Metallic9896

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darks said:
Any tips for structural isomers etc?
for cis trans... "2^no of double bonds"
for optical... "2^no of chiral carbons"
for stereoisomers... "2^no of chiral carbons+double bonds"
The double bonds are of of course cis trans C=C only.
Click to expand...

Hmm yeah these are good formulae but there are exceptions so I just do the counting on the spot lol and I leave isomers for the end so that's a major tip. Skip isomer questions. Do em at the end. XD
 
M

Metallic9896

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SohaibButt said:
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Click to expand...

3.

R to S is -134
S to R is +134
S to U is +92
U to S is -92
U to T is -75
T to U is +75

Statement 1: U to R = U to S + S to R = -92 + 134 = +44 so it's true
Statement 2: T to S = T to U + U to S = +75 + -92 = exothermic, not endothermic
Statement 3: Knowing that 2 is incorrect and 1 is correct, you can jump for D as the answer cause there is no '1 and 3', but just to prove that 3 is incorrect, R to T = R to S + S to U + U to T = -134 + 92 + 75 = +33, while they say -33, so incorrect.
 
M

Metallic9896

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SohaibButt said:
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4.
A: D without a charge has 1 proton and 1 neutron and 1 electron. D- would have 1 proton 1 neutron 2 electrons, so it has more electrons than protons but not more protons than neutrons.
B: H3O without a charge has 10 protons 10 electrons and 8 neutrons, with + charge it loses 1 electron and has 9 electrons 10 protons 8 neutrons, so it has more protons than neutrons but not more electrons than protons.
C: OD without charge has 9 protons 9 electrons and 9 neutrons, after - charge has 10 electrons 9 protons 9 neutrons, more electrons than protons but not more protons than neutrons.
D: OH without charge has 9 protons 9 electrons and 8 neutrons, after - charge has 10 electrons 9 protons 8 neutrons, which fulfills conditions, making it ther ight answer.
 
Mstudent

Mstudent

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ughkno said:
can one of you help me with this? I can't understand why the answer is B - thanks
Click to expand...
Yo, dilute acid and dilute base (Dil HCL and H2SO4) react with esters to hydrolyse it. Sodium only reacts with Carboxyllic acids and alcohols, but there aren't any!

hope this helps!! :)
 
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