Chemistry: Post your doubts here!

[Hadi Murtaza]

Please anyone Q5
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_12.pdf
The ans is C

Enthalpy change = Σ(ΔH Products) - Σ(ΔH Reactants)
Enthalpy change = [ (90.3 × 4) + (- 241.8 × 6) ] - [ - 461.4 × 4 ]
Enthalpy change = [ 361.2 - 1450.8 ] + 184.4
Enthalpy change = - 905.2 kJ/mol

 

[ZaqZainab]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w04_qp_1.pdf
Q4
Q19
Q21 i have difficulty on finding a ciral carbon from rings any tips?
Q33 what about 3? more the concentration lower the activation energy?
Q35 waht about2 won't CO2 and O2 be made with it?
Q39 how do we make out that it reacts with sodium
Help please

 

[pikachu]

Does anybody have explanations for chemistry mcqs?

 

[DeViL gURl B)]

Guys need a piece of advice.. I sorta messed up in my paper 2 .. Like sorta .. So insha Allah I'll get an A ..
But it is still possible to get an A ... It is right?
Btw I just did some silly mistakes in that paper..

 

[Metanoia]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w04_qp_1.pdf
Q4
Q19
Q21 i have difficulty on finding a ciral carbon from rings any tips?
Q33 what about 3? more the concentration lower the activation energy?
Q35 waht about2 won't CO2 and O2 be made with it?
Q39 how do we make out that it reacts with sodium
Help please

Q4. The top number is mass number (proton + neutron), to find the protons, you need to refer to Periodic Table

A. Bi : 83 protons, 126 neutrons
B. Pb : 82 protons, 126 neutrons
C. Po : 84 protons, 126 neutrons
D. Tl : 81 protons, 127 neutrons
So Tl is "unstable" as it does not contain 126 neutrons.

Q19. Form the equation based on the information given.

(NH4)2SO4 + 4O2 --> H2SO4 + 2HNO3 + 2H2O

Q21. The carbons on the "ring" are benzene carbons, they do not have 4 bonds to bond to 4 different groups, so we need not
check them for "chirality".

Q35. CaCo3 --> CaO + CO2

Q39. The hydroxyl (OH) group reacts with sodium to from hydrogen gas.

 

[Metanoia]

Does anybody have explanations for chemistry mcqs?

Could I confirm the date of the chemistry paper?

 

[ashcull14]

JUNE 2004 MCQ 28 PLX HELP URGENT

 

[ashcull14]

Could I confirm the date of the chemistry paper?

10 june

 

[Metanoia]

JUNE 2004 MCQ 28 PLX HELP URGENT

s04qp1

Use the 4 options and trial and error.

Before dehydration, the C=C bonds were actually CH-COH.

Check which of the 4 could possibly give us a tertiary alcohol (resistant to oxidation) before dehydration.

In this case, it was D.

 

[Gehad Mohamed]

Hi can someone please tell me why the product is a carboxylic acid not aldehyde while they mentioned distillation takes place !
Q 25 http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_13.pdf

 

[Hassan Ali Abid]

Hi can someone please tell me why the product is a carboxylic acid not aldehyde while they mentioned distillation takes place !
Q 25 http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_13.pdf

Its clearly written that ' The reaction mixture was then boiled under reflux for one hour' so this means that carboxylic acid is formed not the aldehyde.

 

[Gehad Mohamed]

Its clearly written that ' The reaction mixture was then boiled under reflux for one hour' so this means that carboxylic acid is formed not the aldehyde.

But they also said distillation ! So plz tell me under which condition will an aldehyde form?

 

[Hassan Ali Abid]

But they also said distillation ! So plz tell me under which condition will an aldehyde form?

aldehyde is formed under the condition of * distill over * not under heat under reflux. Just read the question carefully ...they have said that the acid formed is separated by distillation.
Did you get it or not ???

 

[Metanoia]

But they also said distillation ! So plz tell me under which condition will an aldehyde form?

Honestly, I do see some flaws in the question set.

I believe they intend for students to interpret in this manner.
1st part of experiment: Reflux to oxidize alcohol to acid.

2nd part of experiment: Distillation to separate mixture of alcohol and acid.

 

[Metanoia]

aldehyde is formed under the condition of * distill over * not under heat under reflux. Just read the question carefully ...they have said that the acid formed is separated by distillation.
Did you get it or not ???

For discussion's sake, when the question says the product is collected by distillation. What do you think the distillate is?

 

[Hassan Ali Abid]

For discussion's sake, when the question says the product is collected by distillation. What do you think the distillate is?

The distillate will be an acid bcz they have said that the product formed is collected by distillation.

 

[Metanoia]

The distillate will be an acid bcz they have said that the product formed is collected by distillation.

Which is my point of concern. Cause the acid should the higher point compared to alcohol.
The only sense i can make it it is they collect the alcohol distillate first, then collect the acid.

 

[Hassan Ali Abid]

Which is my point of concern. Cause the acid should the higher point compared to alcohol.
The only sense i can make it it is they collect the alcohol distillate first, then collect the acid.

Exactly thats what i was thinking but did u notice the wording of question??? -_-

2.76 g of ethanol were mixed with an excess of aqueous acidified potassium dichromate(VI). The
reaction mixture was then boiled under reflux for one hour. The organic product was then
collected by distillation.
The yield of product was 75.0%.
What mass of product was collected?

There you see we have to consider the Acid formed not the Alcohol and who cares if we get acid or an Alcohol as a distillate.

 

[Metanoia]

Exactly thats what i was thinking but did u notice the wording of question??? -_-

2.76 g of ethanol were mixed with an excess of aqueous acidified potassium dichromate(VI). The
reaction mixture was then boiled under reflux for one hour. The organic product was then
collected by distillation.
The yield of product was 75.0%.
What mass of product was collected?

There you see we have to consider the Acid formed not the Alcohol and who cares if we get acid or an Alcohol as a distillate.

Well, for MCQ, it doesn't really matter. Like i said, its just for discussion purpose, maybe will make a difference if its a theory paper where we need to design experiment procedure.

 

[Gehad Mohamed]

Exactly thats what i was thinking but did u notice the wording of question??? -_-

2.76 g of ethanol were mixed with an excess of aqueous acidified potassium dichromate(VI). The
reaction mixture was then boiled under reflux for one hour. The organic product was then
collected by distillation.
The yield of product was 75.0%.
What mass of product was collected?

There you see we have to consider the Acid formed not the Alcohol and who cares if we get acid or an Alcohol as a distillate.

Mass differs because if aldehyde u get ans A if carboxylic acid ans is c