AS Chemistry P2 Prep.

[Rashmit Arora]

http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w09_qp_21.pdf

Q.5. b,iii)

What do you get J as? Mark scheme says hydroxyacid. I don't know how. Anyone care to explain? Thanks

 

[mujtabashahnawaz]

yeah but i cant seem to get the answer..could you do the working please?

ok.
take ratio of 50: 300 :200 that will be 1 : 6 : 4,
the equation becomes
CH + 6 O2------> 4 CO2 + H2O
Now balance O2:
CH + 6O2------> 4 CO2 + 4 H2O
Now, calculate no of C and H atoms in products:
C: 4 *1= 4
H: 4*2 = 8
These will be the same in CH, so the formula will be C4H8!

 

[mujtabashahnawaz]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_21.pdf

Q.5. b,iii)

What do you get J as? Mark scheme says hydroxyacid. I don't know how. Anyone care to explain? Thanks

It is hydroxy acid because as it has 3 C, and the emperical formula should be CH2O so the molecular formula is C3H6O3.
It gives effervescence with Na2CO3, it means it should be acid and alcohol , because not one but 3 O are there>... 1 for OH and the other 2 for COOH!

 

[Rashmit Arora]

It is hydroxy acid because as it has 3 C, and the emperical formula should be CH2O so the molecular formula is C3H6O3.
It gives effervescence with Na2CO3, it means it should be acid and alcohol , because not one but 3 O are there>... 1 for OH and the other 2 for COOH!

Thank you! Good explanation, missed out on the empirical bit.

 

[mujtabashahnawaz]

Thank you! Good explanation, missed out on the empirical bit.

 

[USMAN Sheikh]

need help q1 part c ?? is ms wrong ?? pls

 

[USMAN Sheikh]

need help q1 part c ?? is ms wrong ?? pls

Need help i got ans 4/9 is my ans correct ?????

 

[mujtabashahnawaz]

Need help i got ans 4/9 is my ans correct ?????

No you are not correct, the amount of moles of CH3COOH is 0.04 at equilibrium, so the same should be for ROH, while 0.06 moles are for two products each. so kc: (0.06)(0.06)/(0.04)(0.04)
the answer comes 9/4

 

[littlecloud11]

when 50cm^3 of a hydrocarbon Y is burnt it reacts with exactly 300 cm^3 of oxygen to form 200 cm^3 of C02. water is also formed. deduce the equation for this reaction. answer: C4H8 + 6O2 → 4CO2 + 4H2O..please tell the how to work this one out..its frm chemistry coursebook.

no of moles of hydrocarbons that reacted= 50/24000 = 2.1x10^-3 [1 mole of the hydrocarbon occupies 24 dm^3= 24000 cm^3]
no on moles of O2= 300/24000 =.0125
no of moles of CO2= 200/24000 = 8.3x10^-3

now divide the number of moles of CO2 and O2 by the number of moles of the hydrocarbon to find how many of each reacted and was formed from 1 mole of the hydrocarbon.

you get 1 mole of HC reacted with 6 moles of O2 [.0125/ 2.1x10^-3 = 6] and formed 4 moles of CO2 [8.3x10^-3/ 2.1x10^-3 = 4]
now balance the equation to get the number of moles of H2o!

 

[mujtabashahnawaz]

no of moles of hydrocarbons that reacted= 50/24000 = 2.1x10^-3 [1 mole of the hydrocarbon occupies 24 dm^3= 24000 cm^3]
no on moles of O2= 300/24000 =.0125
no of moles of CO2= 200/24000 = 8.3x10^-3

now divide the number of moles of CO2 and O2 by the number of moles of the hydrocarbon to find how many of each reacted and was formed from 1 mole of the hydrocarbon.

you get 1 mole of HC reacted with 6 moles of O2 [.0125/ 2.1x10^-3 = 6] and formed 4 moles of CO2 [8.3x10^-3/ 2.1x10^-3 = 4]
now balance the equation to get the number of moles of H2o!

Yeah, this method is correct too

 

[littlecloud11]

Yeah, this method is correct too

Gee, thanks.

 

[USMAN Sheikh]

No you are not correct, the amount of moles of CH3COOH is 0.04 at equilibrium, so the same should be for ROH, while 0.06 moles are for two products each. so kc: (0.06)(0.06)/(0.04)(0.04)
the answer comes 9/4

but these are the reacted moles right the moles reacted of naoh and acid are 0.04 hence at equilibrium, tey suld be 0.1 - 0.04 =0.06 so why my ans wrong ???? :S :|

 

[littlecloud11]

but these are the reacted moles right the moles reacted of naoh and acid are 0.04 hence at equilibrium, tey suld be 0.1 - 0.04 =0.06 so why my ans wrong ???? :S :|

After the reaction of ethanoic acid with the alcohol were complete the REMAINING moles of acid was titrated with NaOH. Since .04 moles of the acid reacted with NaOH, the amount of moles of acid present after equilibrium must be .04, so .06 had already been used in the reaction with the alcohol.
hence acid=alcohol=.04 AT EQUILIBRIUM
and product moles= .06 at equilibrium

 

[leosco1995]

but these are the reacted moles right the moles reacted of naoh and acid are 0.04 hence at equilibrium, tey suld be 0.1 - 0.04 =0.06 so why my ans wrong ???? :S :|

I think you are assuming ROH is NaOH. It's not, ROH is the alcohol. If 0.04 reacted with NaOH, it means the remaining 0.06 moles reacted with the alcohol.

 

[haider159]

plz help me with "question 5 part (b)" of this paper and plz explain me how u did that. thanx

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w08_qp_2.pdf

 

[oldfashionedgirl]

plz help me with "question 5 part (b)" of this paper and plz explain me how u did that. thanx

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w08_qp_2.pdf

its molecular formula is C4H8O2 right? well u see u've got about 4 carbon atoms so to form the esters,just keep changing the number of carbon atoms of the alcohol or carboxyllic part of the ester.
Let us consider the alcohol part. In the first isomer keep the carbon atoms in alcohol,like, 3 since u've got to leave atleast one carbon atom for the carboxyllic acid as well. Then in the next change it to 2. Then finally to 1,like this:


1) HCOOCH2CH2CH3
2) CH3COOCH2CH3
3) CH3CH2COOCH3

For the fourth isomer, consider the structure of the first isomer i've written and just take the last carbon atom that is, the methyl group and shift it to the second carbon atom from left. That way u'll get,

4) HCOOCH (CH3) CH3

Got it?

 

[mujtabashahnawaz]

plz help me with "question 5 part (b)" of this paper and plz explain me how u did that. thanx

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w08_qp_2.pdf

Just shuffle the atoms but do not disturb part which is ester.

 

[mujtabashahnawaz]

its molecular formula is C4H8O2 right? well u see u've got about 4 carbon atoms so to form the esters,just keep changing the number of carbon atoms of the alcohol or carboxyllic part of the ester.
Let us consider the alcohol part. In the first isomer keep the carbon atoms in alcohol,like, 3 since u've got to leave atleast one carbon atom for the carboxyllic acid as well. Then in the next change it to 2. Then finally to 1,like this:


1) HCOOCH2CH2CH3
2) CH3COOCH2CH3
3) CH3CH2COOCH3

For the fourth isomer, consider the structure of the first isomer i've written and just take the last carbon atom that is, the methyl group and shift it to the second carbon atom from left. That way u'll get,

4) HCOOCH (CH3) CH3

Got it?

good explaination

 

[oldfashionedgirl]

good explaination dude

why does everyone keep calling me 'bro' and 'dude' eventhough my username so clearly states my gender
ur welcome,btw

 

[mujtabashahnawaz]

why does everyone keep calling me 'bro' and 'dude' eventhough my username so clearly states my gender
ur welcome,btw

lolz...after i posted my comment then i saw ur profile pic, and then i realised that u are a girl