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Chemistry: Post your doubts here!

A

A star

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scouserlfc said:
Can anyone solve Q34 of the following paper i dont know why answer is A ???

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_12.pdf
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well for the first
1)H2SO4 is the stronger acid then ethanoic acid hence it will proceed a more rapid reaction having higher temprature
2) acording to balanced equation we need 2 moles of ethanoic acid while one mole of sulphuric acid to produce one mole of hydrogen gas and since equal amount of reactants used it will have higher amount of H2 during and after reaction
 
scouserlfc

scouserlfc

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A star said:
well for the first
1)H2SO4 is the stronger acid then ethanoic acid hence it will proceed a more rapid reaction having higher temprature
2) acording to balanced equation we need 2 moles of ethanoic acid while one mole of sulphuric acid to produce one mole of hydrogen gas and since equal amount of reactants used it will have higher amount of H2 during and after reaction
Click to expand...

OH wow,now Im going to write everything ! Im tired of these stupid errors :p
 
daredevil

daredevil

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Warrior66 said:
Asalam-o-Alaikum!
can anyone please help me with these
questions? http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_11.pdf
Questions: 9, 21, 26 and 28
thanks a lot..!
Click to expand...
26 is C??
look first sibgle out the aldeydes because Tollen's test is positive in aldehydes only NOT in ketones.. :
W => 2 funtional groups ketone and alcohol so not this
X => although X has a ketone group it also has an aldehyde group at the right end so it is good to go
Y=> does not have an aldehyde group
Z => has an aldehyde group at the right end

so we narowed it down to X and Z. Both of these can be oxidised by Maganate ion so they both fit the conditions. hence the answer C.

I hope i'm right :p :cautious:
 
Warrior66

Warrior66

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daredevil said:
26 is C??
look first sibgle out the aldeydes because Tollen's test is positive in aldehydes only NOT in ketones.. :
W => 2 funtional groups ketone and alcohol so not this
X => although X has a ketone group it also has an aldehyde group at the right end so it is good to go
Y=> does not have an aldehyde group
Z => has an aldehyde group at the right end

so we narowed it down to X and Z. Both of these can be oxidised by Maganate ion so they both fit the conditions. hence the answer C.

I hope i'm right :p :cautious:
Click to expand...
ooh yes Alhamdullilah I got it now...yup the answer's "C". (y) thanks a bunch!
daredevil said:
couldn't get the others ..... tag me in the answers wen u get em plz ^_^
best of luck for ur papers :)
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okay no problem, sure will. thanks, you too! :)
 
iKhaled

iKhaled

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ImmadPanhwar said:
sorry :p its may june 2009 22 Q3 D ii
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lets say that at equilibrium CO2 and H2 will both lose "x" amount of moles which means that CO and H2O will gain x amount of moles so kc will be

kc = [H2O][CO]/[CO2][H2] it is given that kc is 1.44 so
1.44 = (0.2+x)(0.2+x)/(0.5-x)(0.5-x)
1.44(0.5-x)^2 = (0.2+x)^2

find x then use it to calculate the amount of moles of co2, co h2 and h20 at equilibrium..got it ?
 
ImmadPanhwar

ImmadPanhwar

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iKhaled said:
lets say that at equilibrium CO2 and H2 will both lose "x" amount of moles which means that CO and H2O will gain x amount of moles so kc will be

kc = [H2O][CO]/[CO2][H2] it is given that kc is 1.44 so
1.44 = (0.2+x)(0.2+x)/(0.5-x)(0.5-x)
1.44(0.5-x)^2 = (0.2+x)^2

find x then use it to calculate the amount of moles of co2, co h2 and h20 at equilibrium..got it ?
Click to expand...
thank you (y)
 
Razo513

Razo513

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daredevil said:
26 is C??
look first sibgle out the aldeydes because Tollen's test is positive in aldehydes only NOT in ketones.. :
W => 2 funtional groups ketone and alcohol so not this
X => although X has a ketone group it also has an aldehyde group at the right end so it is good to go
Y=> does not have an aldehyde group
Z => has an aldehyde group at the right end

so we narowed it down to X and Z. Both of these can be oxidised by Maganate ion so they both fit the conditions. hence the answer C.

I hope i'm right :p :cautious:
Click to expand...
Warrior66 said:
Asalam-o-Alaikum!
can anyone please help me with these
questions? http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_11.pdf
Questions: 9, 21, 26 and 28
thanks a lot..!
Click to expand...

#9) idk :p


#21) organic compounds that react with sodium are either carbonal acids or alcohols ... organic ion with a charge of -3 means that there are 3 charged group or in other words three groups in the compound that could react , j reacts with NaOH to give a compound with charge -1 meaning that 2 of the charged groups will react the other wont .. thus it should have 2 acid groups and 1 alcohol group which wont react with NaOH answer=C


#26) compounds that could be oxidised by acidified dichromate are alcohols,ketones & aldehydes .. but then only aldehydes give a positive result with tollen's so the compounds should contain both alcohol aldehyde .. the only answer which works is C

#28) the graph shows a reaction that is done in 2 steps & is exothermic the only one which fits is B which is SN2 reaction
 
KurayamiKimmi

KurayamiKimmi

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Asalamo Alaikum!:)

I came aross this line in the mark scheme for P5 --
Candidate draws a straight line which passes through (0,0) or would pass through (0,0) if extrapolated
Click to expand...

Could anyone clarify what this means?
 
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