Chemistry: Post your doubts here!

[AbbbbY]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s06_qp_1.pdf
Q2

3 peaks; 35 35, 35 37, 37 37

 

[AbbbbY]

Oh my. Just saw I was wasting time on answered questions. Opened the thread and it took me a few pages back -___-

 

[Fma 07]

hey

Jazaka'Allah Thankyou

 

[daredevil]

An organic compound, X, will react with an excess of calcium metal to produce a salt with the
empirical formula CaC4H6O4.

What could be the identity of X?
1 ethanoic acid
2 butanedioic acid
3 methylpropanedioic acid

ethanoicc acid??

bcz 2 organic molecules will be needed to balance out the 2+ valency of Ca

 

[daredevil]

3 peaks; 35 35, 35 37, 37 37

i dont get this one

 

[Eshika]

ethanoicc acid??

bcz 2 organic molecules will be needed to balance out the 2+ valency of Ca

yes it is ethanoic acid but how do u get the empirical formula that they have given to us ?

 

[Zarif009]

all kinds i think

I appreciate it but thats not the right answer...

some reactions such as enthalpy change from the combustion of glucose can be obtained just by using a calorimeter so Hess's Law is not needed...

 

[daredevil]

yes it is ethanoic acid but how do u get the empirical formula that they have given to us ?

look Ca2+ needs 2(-1) to balance it out ryt??
if we take two of ethanoic acids it gives us C4H6O4
if we take 2 butanedoic acid it gives us something with eight C and with mmethypropanadoic acid is the same case...
only ethanoic acid gives the correct formula. remember to use 2 acids not 1 to balance out the one Ca.

 

[daredevil]

I appreciate it but thats not the right answer...

some reactions such as enthalpy change from the combustion of glucose can be obtained just by using a calorimeter so Hess's Law is not needed...

i didn't say we definitely need Hess for all the enthalpy changes but it is always possible to solve these questions with Hess if nothing else works.
it is just a method. and one that applies to all so that makes it handy if u have a good grip on Hess's law u don't need to work with other methods and formulae and stuff just putt in a Hess's triangle and u got ur thing going. that's wat i am saying

 

[Eshika]

look Ca2+ needs 2(-1) to balance it out ryt??
if we take two of ethanoic acids it gives us C4H6O4
if we take 2 butanedoic acid it gives us something with eight C and with mmethypropanadoic acid is the same case...
only ethanoic acid gives the correct formula. remember to use 2 acids not 1 to balance out the one Ca.

ohh!! ok thnx alot!!!!

 

[1357913579]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w09_qp_1.pdf
number-28
thnks

anyone?

 

[zackle09]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w10_qp_12.pdf

have been doing question 22 for so long..but im not getting 16
can someone plsss do it

 

[syed1995]

anyone?

The product gets oxidized.. both the C=C bonds will be broken... CH2 forms CO2 + H2O .. .. CHR forms aldehyde .. and CRR` forms Ketone..

So final product becomes ..

Answer is 3.

 

[syed1995]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_12.pdf

have been doing question 22 for so long..but im not getting 16
can someone plsss do it

Y = Products formed with reaction with CN + acid .. = CH3+CH(OH)COOH

Z = Product formed after oxidation is = CH3CH2COOH ..

The only difference in both is that Y has one more O then Z. so the difference in mass is 16.

 

[1357913579]

The product gets oxidized.. both the C=C bonds will be broken... CH2 forms CO2 + H2O .. .. CHR forms aldehyde .. and CRR` forms Ketone..

So final product becomes ..

Answer is 3.

thanks for ur try bro but i asked for november 2009 which u can see on my post please help me at that
thanks

 

[zackle09]

Y = Products formed with reaction with CN + acid .. = CH3+CH(OH)COOH

Z = Product formed after oxidation is = CH3CH2COOH ..

The only difference in both is that Y has one more O then Z. so the difference in mass is 16.

oh i get it now.. thanks so much!

 

[1357913579]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s10_qp_11.pdf
number-21 why not 4?
number-27
thanks

 

[AbbbbY]

i dont get this one

Two atoms of Chlorine 35 can bond
One atom of Chlorine 35 and one atom of Chlorine 37 can bond
Two atoms of Chlorine 37 can bond

Thus, giving 3 peaks.

 

[syed1995]

thanks for ur try bro but i asked for november 2009 which u can see on my post please help me at that
thanks

That was the paper which you linked :\

 

[AbbbbY]

Q1's answer is C. from the data u can infer that 50 cm3 of O2 was used to burn 10cm3 of hydrocarbon (CxHy)
make up an equation for the unknown hydrocarbon for ur aid and u'll c that 1 mol of CxHy requires 5 moles of O2 to produce 3 mol of CO2. 6 O go into the CO2 and the remaining 4 (from 5 O2) go to the H2O which means that 4 H2O molecules were formed. so we have 8 H and 3 C thus the ansewr.

Q2's answer is bcz 2 mol of NaN3 make 3 mol of N2 which means 1 mol makes 1.5 mol of N2 directly. then the Na produced also makes N2.
wth 2 mol of NaN3 we get 2 mol of Na so with 1 mol we get 1 mol of Na.
10 mol of Na produce 1 mol of N2 so 1 mol produces 0.1 mol
so total N2 produced is 1.5 + 0.6 = 1.6mol

i don't get q10 so if u get an answer for that tag me ^_^

Q10:

Kp = ((2/3)^2)/(1/3)

= 4/9 / 1/3
= 4/9 * 3/1
= 4/3

Units: atm*atm/atm = atm