Chemistry: Post your doubts here!

[Holmes]

You just need to understand these:

Pressure is DIRECTLY PROPORTIONAL to Temperature p=nt
Pressure is INDIRECTLY PROPORTIONAL to volume p=n/v where n is a constant

from there you derive the equations 1V1=P2V2, P1/T1 = P2/T2, P1V1/T1 = P2V2/T2

Its pretty simply if you can understand the relationship!!!

hope that helps

thanks

 

[Mstudent]

For ques 16

 

[Holmes]

http://papers.gceguide.com/A Levels/Chemistry (9701)/9701_w16_qp_13.pdf
Please Explain :
Q 3 ,20, 37 and 16

First look at Q 16


Write eq… of decomposition of Mg(NO3)2

2 Mg(NO3)2------------ 2 MgO + 4 NO2 + O2

He wants mass of oxide of Nitrogen ,X

Now find Mr of Mg(NO3)2 i.e = 148.3

Finding moles = 7.4/148.3

= 0.05 moles

Look at the mole ratio of NO2 and Mg(NO3)2 you get

2:4

= 1:2

So moles of NO2 = 0.05*2

= 0.1 moles

To find the mass of NO2 we need MR of NO2 i.e. =46

Finally, Mass = 46*0.1

= 4.6 g

 

[Mstudent]

Someone from here actually told us the trick before

Take the two equations from the data booklet and balance the two equations

 

[Mstudent]

Anyone????

 

[Holmes]

Anyone????

Nitrogen atom has two lone pairs and one single electron in it (N atomic no. 7 )
when CH3NCO is formed then
a double bond is formed between N and C .... here nitrogen's one lone pair is utilized in making bond,
and ONE single electron is used to make a Single bond with CH3 .
Now , N has only one lone pair that is not involved in any bonding.
so the figure is sth like:
bond pairs = 2 Lone pair = 1 we will count a Double bond as a SINGLE bond ( or one bond pair)
so this figure will give us an angle of 119' or 120'
Aswer = C
Hope it make sense!

 

[Mstudent]

Thank you very much!!, I confused it mistakenly with water, I didnt realise water had 2 lone pairs

 

[Mstudent]

ANYONE!!

 

[SohaibButt]

Please anyone?

 

[Mstudent]

Anyone could help me with q.9
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s14_qp_11.pdf

 

[amina1300]

Anyone could help me with q.9
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s14_qp_11.pdf

ONLY THE LAST ONE CANCELS OUT.

 

[Mstudent]

View attachment 62368
ONLY THE LAST ONE CANCELS OUT.

Thank you very much amina1300 .

 

[amina1300]

Please anyone?

Q10 Ans = C
Kc>1 tells you that the equilibrium will lie to the right,
H2(g) + I2(g) <==> 2HI(g) .................. Kc = 60.
2M .......0.3M ............?M

Kc = [HI]² / ([H2] [I2])
60 = x² / 2 / 0.3
x = 6
[HI] = 6M
moles of HI = 6

Q5
Q=VxCxdeltaT
total volume is 25+25 = 50 cm3
= 50 x 4.3 x (2.5)
=525
now we shud find enthalpy change fore one mole
number of moles = vol. x conc.
25/1000 x 0.35 = 8.75x10^-3


525 Joules was for 8.75x10^-3 moles
525 J = 8.75x10^-3 moles
? = 1 mole
525/(8.75x10^-3) = 60000 Joules/mole

TIP: If we need to guess an option without calculation, the heat of neutralization of a strong acid and strong alkali should be in the region of ~58 kJ mol–1.

Last Q :
Kc = x/(7.6x10^-6)^4*x
Kc = 2.997..x10^20 Ans = A

 

[amina1300]

ANYONE!!

View attachment 62361

"N" + ½O2 → NO nitric oxide (gas)
NO + ½O2 →fast→ NO2 nitrogen dioxide
NO is diatomic
And it is polar as it contains electro-negative N

I think A is correct .... ?

 

[Mstudent]

"N" + ½O2 → NO nitric oxide (gas)
NO + ½O2 →fast→ NO2 nitrogen dioxide
NO is diatomic
And it is polar as it contains electro-negative N

I think A is correct .... ?

Yeah you're right, thank you very much!

 

[amina1300]

http://papers.gceguide.com/A Levels/Chemistry (9701)/9701_w16_qp_13.pdf
Q37 and 20 Anyone??

 

[Mstudent]

http://papers.gceguide.com/A Levels/Chemistry (9701)/9701_w16_qp_13.pdf
Q37 and 20 Anyone??

For q. 37

1 will react to form propanone and 2-methyl propanoic acid
2 will also form a Carboxyllic aid and a ketone
3.will also for a carboxyllic acid and a ketone

so I suppose its A?

 

[amina1300]

For q. 37

1 will react to form propanone and 2-methyl propanoic acid
2 will also form a Carboxyllic aid and a ketone
3.will also for a carboxyllic acid and a ketone

so I suppose its A?

How do you know that what will form ..can you explain in detail? :/ I'm really bad at Organic Chemistry.

 

[Mstudent]

How do you know that what will form ..can you explain in detail? :/ I'm really bad at Organic Chemistry.

Oh. OK so here's the rule

IF a C=C is broken by:

1. COLD KMNO4-------> two OH groups will BE ADDED (Electrophillic addition) and form a Diol
2. HOT CONCENTRATED KMNO4---------> 3 Conditions
A. If NO Carbon groups joined to C in C=C------> CO2 and H2O
B. If ONE Carbon group joined to C in C=C ---------> Aldehyde---------> Carboxyllic acid (Write only the Carboxyllic acid in exams)
C. If TWO Carbon groups joined to C in C=C-------------> ketone

Thats it!

hope that helps

 

[amina1300]

Oh. OK so here's the rule

IF a C=C is broken by:

1. COLD KMNO4-------> two OH groups will BE ADDED (Electrophillic addition) and form a Diol
2. HOT CONCENTRATED KMNO4---------> 3 Conditions
A. If NO Carbon groups joined to C in C=C------> CO2 and H2O
B. If ONE Carbon group joined to C in C=C ---------> Aldehyde---------> Carboxyllic acid (Write only the Carboxyllic acid in exams)
C. If TWO Carbon groups joined to C in C=C-------------> ketone

Thats it!

hope that helps

OMg that was extremely helpful I can't thank you enough!
I couldn't comprehend this in question but thanks to you now I just realized that we look at both sides of the C=C