Chemistry: Post your doubts here!

[kingo44]

C H-c=0-O-ch2ch2CH3

 

[kingo44]

D H3C-CH-c=o-0H
CH3

 

[kingo44]

Q29

 

[Zepudee]

donno wht mistake am i committing
View attachment 45079

is it C? 940+2(-110)= +720

 

[Hinafatima]

please,may i get helped in q# 35 for may june 2013 variant 13 , answer is C ?thanks

 

[Browny]

Please help as I don't understand how to get the reaction 2 answer.

 

[kingo44]

ok guyz please naoh reatcs with carboxylic acids but not alcohol right ok naoh reats with carboxylic acid then how many moles of na will be formed in carbxylate ion

 

[Hinafatima]

View attachment 45081

Please help as I don't understand how to get the reaction 2 answer.

is the answer B? if so then it means reaction 1 is endo as it requires heat to decompose calcium carbonate, and reaction 2 is exo in nature as hydration is always exo

 

[Browny]

is the answer B? if so then it means reaction 1 is endo as it requires heat to decompose calcium carbonate, and reaction 2 is exo in nature as hydration is always exo

Yes it is B, but isn't reaction 2 a reaction enthalpy of a solution and can you please give me the definition of enthalpy of hydration.

The enthalpy change of solution is the enthalpy change when 1 mole of an ionic substance dissolves in water to give a solution of infinite dilution.

 

[loveyuan]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s08_qp_1.pdf

No 39 it is statement 2 is correct ? i though only ONE chiral center formed? since another C from the alkene is already chiral

 

[kingo44]

21 An organic compound J reacts with sodium to produce an organic ion with a charge of –3.
J reacts with NaOH(aq) to produce an organic ion with a charge of –1.

What could be the structural formula of J?
A HO2CCH(OH)CH2CO2H
B HO2CCH(OH)CH2CHO
C HOCH2CH(OH)CH2CO2H
D HOCH2COCH2CHO

 

[Browny]

is the answer B? if so then it means reaction 1 is endo as it requires heat to decompose calcium carbonate, and reaction 2 is exo in nature as hydration is always exo

The enthalpy change of solution is the enthalpy change when 1 mole of an ionic substance dissolves in water to give a solution of infinite dilution.

 

[loveyuan]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s08_qp_1.pdf

question 2 and 6 please help T_T

 

[Hinafatima]

Yes it is B, but isn't reaction 2 a reaction enthalpy of a solution and can you please give me the definition of enthalpy of hydration.

The enthalpy change of solution is the enthalpy change when 1 mole of an ionic substance dissolves in water to give a solution of infinite dilution.

The heat energy released when new bonds are made between the ions and water molecules is known as the hydration enthalpy of the ion.

The hydration enthalpy is the enthalpy change when 1 mole of gaseous ions dissolve in sufficient water to give an infinitely dilute solution. Hydration enthalpies are always negative.

 

[Hinafatima]

The heat energy released when new bonds are made between the ions and water molecules is known as the hydration enthalpy of the ion.

The hydration enthalpy is the enthalpy change when 1 mole of gaseous ions dissolve in sufficient water to give an infinitely dilute solution. Hydration enthalpies are always negative.

and secondly in my opinion , heat of solution is the difference between lattice dissociation enthalpy and hydration enthalpy

 

[loveyuan]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s08_qp_1.pdf

question 2 and 6 please help T_T

 

[Browny]

and secondly in my opinion , heat of solution is the difference between lattice dissociation enthalpy and hydration enthalpy

The enthalpy change of solution is the enthalpy change when 1 mole of an ionic substance dissolves in water to give a solution of infinite dilution.

This is the definition and in the above case CaO is the ionic substance dissolved in water. Isn't that so?

 

[Zepudee]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w08_qp_1.pdf
Hello!! Q11 (A) , Q30 (C) [ why i keep getting A ] and Q39 (B) [ what is thissss!! ]

 

[Zepudee]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s08_qp_1.pdf

question 2 and 6 please help T_T

for Q2
15/100 x 14 =2.1g of N
basically it is the mole : the 15/100
So, 0.15 mole
And 0.15/5 = 0.03 dm3

 

[kingo44]

q 39
74.00g of butan-2-ol → 44.64 g of butanone

Moles of butan -2 -ol =1
moles of butanone= Mass/mr
=44.64/72= 0.62

now in theory 1 mole of butan 2 ol produces 1 mole of butanone.
but we got 0.62 moles of butanone
hence 62 percent yield

Use the same method for the rest of the reactions and you will gt 62 percent yield for all of them.

q 40
(CH3)3CBr + NaOH → (CH3)3COH + NaBr

(CH3)3CBr is a tertiary haloalkane .
It has three R groups attached to the Carbon bonded to the halogen
Only Tertiary haloalkanes undergo SN1 mechanism for nucleophillic substituition.
This is because tertiary haloalkanes have electron donationg methyl groups attached they can form an intermediate and stable carbocation.
The graph has two humps so this means that an intermediate is formed before the reaction proceeds.
2 and 3 are not tertiary haloalkanes so an intermediate is not formed

sometimes two humps also represent sn2 wat to do