Chemistry: Post your doubts here!

[leosco1995]

20 How many alcohols (including both structural isomers and stereoisomers) can have the molecular
formula C4H10O?
A 3 B 4 C 5 D 6

The answer is apparently C.. but I can only draw 4 (none of them being stereoisomers) and every website I've read so far says there's only 4 isomeric alcohols of C4H10O. What's the last one?

EDIT - I'm stupid, I forgot that one of them was an optical isomer, so there's actually 2 of those.

 

[geek101]

mol of metalic salt n= cv

n= (0.10) . (0.050) = 0.0050
mol of sulphite n =cv

n= (0.10) . (0.025) = 0.0025

it has been given that 0.0050 mol of metal reacts with 0.0025 mol of sulphite mol ratio 2:1 metal/ sulphite

now when two electrons are released frm the sulphite's one mole.

only half of the released wil react with one mole of metal as shown above mol ratio 2:1

it has been given that the original oxidation no. of metal is +3 so when 1 elctron wil be added it wil be +2 !!!!


so it wil be the new oxidation no, i guess so B is to be the ans m i ryte??

you are right, thank you

 

[Hinafatima]

There are two possible isotopes for Cl. But the molecule is Cl2. So, there can be three possible peaks.

1. 2 atoms of 35Cl form a Cl2
2. 2 atoms of 37Cl form a Cl2
3. 1 atom of 35Cl and 1 atom of 37Cl form the Cl2.

I dunno what the (+) charge on the Cl2 is about. But I think it has something to do with the mass of an electron being negligible.

you are absolutely right in answering it and as far as the charge is concerned, when we put some thing in mass spectrometer, a gaseous (always) compound changes into an ion due to the knocking off the electron and this process is called ionisation but don't worry it is in A2 sylaabus

 

[xxfarhaxx]

hlp.. doubt!! Q 39
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_12.pdf
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_ms_12.pdf

hw exctly do u calculate %yiled of sumthn????

 

[Soulgamer]

guys urgent ps... hlppp!!!

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s06_qp_1.pdf
Q- 10, 17, 23, 26,33 ,40
god bless u alll!!!

Q.10 N2O4 <---> 2NO2

Initial 100 0

Dissociated 50 100 (Mole ration is 1:2 hence 50 x 2)

Equilibrium 50/150 100/150 (Multiply both by 1 as total atm pressure is 1, answer is still the same) (*150 is total pressure)

1/3 2/3

Kp: (2/3)^2 / (1/3) = 4/3


Q.17 This question is about halogen displacement. Higher Halogen always displaces the lower one.
So, KI + Cl2 ----> KCl + I2
In KI oxidation number of I is -1 and on the right hand side I2 is 0
hence Iodide ions are oxidized to iodine. (-1 to 0)

Q.23 Simple make the organic product and find the Mr of all of them. An easy way to tackle this mentally is that in:

A= The product will be an alcohol hence Br is removed so Mr will be lower [X]
B= An alkene forms, again Mr is lower as H and Br are removed. [X]
C= Final product of free radical substituion is C2Br6. The Mr of Br is 79.9 so 6 will be much much higher than the others. [✔]
D= OH is removed forming haloalkane. Mr increase but not that much. [X]

Q.26 A=Sodium only reacts with Alcohol and bubbles of Hydrogen are evolved [✔]
B= Bromine reacts with Alkenes. Electrophillic addition. [X]

C= KMnO4 oxidises both alcohol and alkene [X]

D= 2,4- DNPH only reacts with aldehyde and ketone. [X]

Q.33 When ever the talk about spontaneously, it means activation energy is too high hence D. 2 is incorrect as in hydrazine triple bond is not present. 3. Hydrazine being a liquid has no effect on its burning spontaneosly.

Q.40. Lactic acid has optical isomers as chiral center is present. The C on the left of OH is chiral. Hydrogen of OH(alcohol can form hydrogen bonding) and Hydrogen in OH of Carboxylic acid can form hydrogen bonding. A secondary alcohol is present hence it will oxidize to a ketone.


I didn't proof read it so yeah. Hope I helped

 

[leadingguy]

hlp.. doubt!! Q 39
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_12.pdf
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_ms_12.pdf

hw exctly do u calculate %yiled of sumthn????

the 74.00g of butan-2-ol is secondary alcohol so wil be converted into ketone (44.64g of butanone)
with the help of H+/Mno4..

then the second is 1 degree so wil be converted to oxilic acid with H+/Mno4

same is the cas with thrd one as was with the second one!
so all conversion r possible

so al is possible A is correct

 

[xxfarhaxx]

Q.10 N2O4 <---> 2NO2

Initial 100 0

Dissociated 50 100 (Mole ration is 1:2 hence 50 x 2)

Equilibrium 50/150 100/150 (Multiply both by 1 as total atm pressure is 1, answer is still the same) (*150 is total pressure)

1/3 2/3

Kp: (2/3)^2 / (1/3) = 4/3


Q.17 This question is about halogen displacement. Higher Halogen always displaces the lower one.
So, KI + Cl2 ----> KCl + I2
In KI oxidation number of I is -1 and on the right hand side I2 is 0
hence Iodide ions are oxidized to iodine. (-1 to 0)

Q.23 Simple make the organic product and find the Mr of all of them. An easy way to tackle this mentally is that in:

A= The product will be an alcohol hence Br is removed so Mr will be lower [X]
B= An alkene forms, again Mr is lower as H and Br are removed. [X]
C= Final product of free radical substituion is C2Br6. The Mr of Br is 79.9 so 6 will be much much higher than the others. [✔]
D= OH is removed forming haloalkane. Mr increase but not that much. [X]

Q.26 A=Sodium only reacts with Alcohol and bubbles of Hydrogen are evolved [✔]
B= Bromine reacts with Alkenes. Electrophillic addition. [X]

C= KMnO4 oxidises both alcohol and alkene [X]

D= 2,4- DNPH only reacts with aldehyde and ketone. [X]

Q.33 When ever the talk about spontaneously, it means activation energy is too high hence D. 2 is incorrect as in hydrazine triple bond is not present. 3. Hydrazine being a liquid has no effect on its burning spontaneosly.

Q.40. Lactic acid has optical isomers as chiral center is present. The C on the left of OH is chiral. Hydrogen of OH(alcohol can form hydrogen bonding) and Hydrogen in OH of Carboxylic acid can form hydrogen bonding. A secondary alcohol is present hence it will oxidize to a ketone.


I didn't proof read it so yeah. Hope I helped

thnx a million!!!

 

[xxfarhaxx]

the 74.00g of butan-2-ol is secondary alcohol so wil be converted into ketone (44.64g of butanone)
with the help of H+/Mno4..

then the second is 1 degree so wil be converted to oxilic acid with H+/Mno4

same is the cas with thrd one as was with the second one!
so all conversion r possible

so al is possible A is correct[/quote

thnx!!!

 

[leadingguy]

hlp.. doubt!! Q 39
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_12.pdf
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_ms_12.pdf

hw exctly do u calculate %yiled of sumthn????

oh fr calculating percentage yield just take the original ones at frst

i.e
if the mass of butan 2 ol is 74 and when it wil react with ioxidising agent it wil lose 2 hydrogen atoms to become

butanone with mass 74 -2 = 72g

now it means that the mss of butanone produced should be 72g frm 74 g of butan 2 ol
but we are having only 44.64g


now calculate the percentage 44.64/ 72 *100 = 62%

 

[Gémeaux]

May/June 2011 9701/12
Q11) 0.144g of an aluminium compound X reacts with an excess of water, to produce a gas. This gas burns completely in O2 to form H2O and 72cm³ of CO2 only. The volume of CO2 was measured at room temperature and presure.
What could be the formula of X?
[C = 12.0, Al = 27.0; 1 mole of any gas occupies 24dm³ at room temperature and pressure]

A Al2C3
B Al3C4
C Al4C3
D Al5C3

 

[xxfarhaxx]

sum mre doubts!!!
Q- 10, 18, 22
http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w10_qp_12.pdf
http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w10_ms_12.pdf

 

[Hinafatima]

The density of ice is 1.00gcm–3
.
What is the volume of steam produced when 1.00 cm3
of ice is heated to 323 °C (596 K) at a
pressure of one atmosphere (101kPa)?
[1mol of a gas occupies 24.0dm3
at 25°C (298K) and one atmosphere.]
A 0.267dm3
B 1.33dm3
C 2.67dm3
D 48.0dm3
please help me somebodyy.....
i cant get the ans.......

Density = mass/vol so mass = D x Vol which would give the mass of ice as 1g. change this mass into moles ,1/18=0.0555 moles.
1 mole of steam occupies the volume at 298K(25c) =24 dm3
0.555 moles of steam would occupy=24 x 0.0555=1.33 dm3
as there is a temperature rise given in the question to 596 K so...
298 K occupies volume =1.33 dm3
1K would occupy............=1.33/298
596K would occupy.......= 1.33/298 x596= 2.67 dm3
i hope its clear.

 

[hm12]

May/June 2011 9701/12
Q11) 0.144g of an aluminium compound X reacts with an excess of water, to produce a gas. This gas burns completely in O2 to form H2O and 72cm³ of CO2 only. The volume of CO2 was measured at room temperature and presure.
What could be the formula of X?
[C = 12.0, Al = 27.0; 1 mole of any gas occupies 24dm³ at room temperature and pressure]

A Al2C3
B Al3C4
C Al4C3
D Al5C3

Its C aluminium carbide
Al4C3+12H2O------->4AL(OH)3+3CH4

CH4+2O2----->2H2O+CO2

Moles of CO2=72/24000=0.003
moles of Al4C3= 0.003/3=0.001 (as ratio of Al4C3:CH4 is 1:3)
now mass of Al4C3= 0.001 into (27+27+27+27+12+12+12)=0.144g

 

[Student12]

QP http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w06_qp_1.pdf
Q1 , 4, 11, 14 ? Can someone xplain & solve ?

QP http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s08_qp_1.pdf
MS http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s08_ms_1.pdf
Q2, 6, 13, 15

 

[xxfarhaxx]

QP http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w06_qp_1.pdf
Q1 , 4, 11, 14 ? Can someone xplain & solve ?

QP http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s08_qp_1.pdf
MS http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s08_ms_1.pdf
Q2, 6, 13, 15

Q1 ANS A:

50cm^3 of H2O containing CaSO4
fr one Ca+ ----> 2H+ ions are xchanged...

find the mols of KOH needed to neutralise da acid here ( in ths cse it H+ ions)
c=n/ v
= (1.0*10^-2)* (25/1000) = 2.5*10^-4 mols

use da molar ratio to find da mols of Ca+ ions
Ca+: H+
1:2
thrfr mols of Ca+ = (2.5*10^-4)/ 2 = 1.25*10^-4 mols of Ca

so nw find da conc of CaSO4 using c=n/v
=(1.25*10^-4) / (50/1000) = 2.5*10^-3 (ANS : A)

 

[Student12]

Q1 ANS A:

50cm^3 of H2O containing CaSO4
fr one Ca+ ----> 2H+ ions are xchanged...

find the mols of KOH needed to neutralise da acid here ( in ths cse it H+ ions)
c=n/ v
= (1.0*10^-2)* (25/1000) = 2.5*10^-4 mols

use da molar ratio to find da mols of Ca+ ions
Ca+: H+
1:2
thrfr mols of Ca+ = (2.5*10^-4)/ 2 = 1.25*10^-4 mols of Ca

so nw find da conc of CaSO4 using c=n/v
=(1.25*10^-4) / (50/1000) = 2.5*10^-3 (ANS : A)

Thanks.

 

[Scafalon40]

That's the reason...remember never to suspect someone until you have a proof

When you could joke, then I can act smart enough to remove that thread completely

anyway better not go off-topic.

But couldn't you just move that thread to another section?
There are other guys whose posts have been locked.
They even meant it, I was just joking dude.
Which brings me back: can't take a joke dude?

 

[smzimran]

But couldn't you just move that thread to another section?
There are other guys whose posts have been locked.
They even meant it, I was just joking dude.
Which brings me back: can't take a joke dude?

No offense brother but..
I think they did the right thing, its not their responsibility to spend time deciding whether you were serious or joking!
They just have to make sure no body goes against the rule!

 

[geek101]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w06_qp_1.pdf Q4 plzzz!

 

[Hinafatima]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w06_qp_1.pdf Q4 plzzz!

option D
Reason: As every option starts with methane so lets check for it.
CH4 + 2O2 ------2 H2O+ CO2
10cm3 of CH4 and 70 cm3 oxygen (given in the question) .According to the equation 1 mole of CO2 requires 2 moles of oxygen so it means if we have 10 cm3 of methane then 20 cm3 of oxygen would be used. 70 minus 20 would give us 50 cm3 which is the residual gas , moreover, in the products CO2 is formed which is also a gas , and as there is 1:1 ratio between CH4 and CO2 so it mean 10 cm3 of CO2 is also formed. 50 +10 gives 60 cm3 and D option's graph starts with the value 60cm3. i hope it helps