Chemistry: Post your doubts here!

[savera]

Right thankyou
btw can u tell me the difference in the reaction of benzene and methyl benzene with br2

The reaction with bromine

The reaction between benzene and bromine takes place with the help of a catalyst such as AlBr3 (if you are reacting with Cl2 then the catalyst will be AlCl3)

Methyl groups are 2,4-directing, which means that incoming groups will tend to go into the 2 or 4 positions on the ring.

OH and CH3 are electron releasing (electron withdrawing) groups, this means that they are 2 ,4 directing group. As in the above diagram the Br2 is in excess so it will take all 3 positions : 2,4,6. If in limited quantity then it will occupy only 2 position.

See the Untitled.png which i have attached. Once you have gone through it you wont have any problem regarding positioning of atoms/molecules e.g Br2 etc

Hope this helps.

 

[danial 234]

why is electron affinity of Chlorine less than that for Fluorine

radius of chlorine is greater than that of flourine. so the force exerted by chlorine nucleus on the electron is less than that exerted by a flourine nucleus

 

[Mahnoorfatima]

Qp 13 ON 12, question number 10 anyone?

 

[Mahnoorfatima]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_12.pdf question 22??

 

[Dark Destination]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_12.pdf question 22??

You just have to look at the values of bond energies from the data booklet and see which one is the lowest..

 

[princess Anu]

please explain...

 

[Mahnoorfatima]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s13_qp_11.pdf q34.?

 

[Mahnoorfatima]

You just have to look at the values of bond energies from the data booklet and see which one is the lowest..

But we don't have the bond energy of C-F? :/

 

[muhammadsaad]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s13_qp_11.pdf q34.?

As we move across the period the ionization energy increses
So the top most peak is of group 8
And the lowest is of group 1 ( shown in the picture)

1 is correct b, j and r are group 8 as highest peak highest ionization across the period

2 is correct as d and l come after lowest peak (group 1) so they are in group 2

3 is correct as g and o are in group 5 and group 5 element have np3 configuration
Take eg of Nitrogen 1s2 2s2 3p3

Phosphorus. 1s2 2s2 2p6 3s2 3p3

P3 means half filled or unpaired electrons

Hope this helps

 

[Dark Destination]

But we don't have the bond energy of C-F? :/

Well, i guess you are supposed to know that C-F will have a comparatively higher bond energy as compared to C-Cl so you don't need to know it's bond energy.
Florine is more electronegative as compared to Chlorine and thus C-F bond is stronger as compared to C-Cl, thus requires more energy to break.

 

[DeadlYxDemon]

Assalamu 3laikum! Firstly I'm really terrible at chemistry, so I've decided to take the exam in the O/N session.
Iz my decision ryt? I mean many of my school teachers say that the checking is strict in O/N session.

 

[princess Anu]

Can somebody highlight those Carbon's

 

[Hinafatima]

I have tried this questions so many times but i am not getting a correct answer. please help.
may june 2014, component 12 Q # 9

 

[Dark Destination]

I have tried this questions so many times but i am not getting a correct answer. please help.
may june 2014, component 12 Q # 9

Link?

 

[Syed Fakhar Hussain]

plz can anyone post good notes of physical chemistry especially bond angles, sp3 hybridization etc??

 

[Mahnoorfatima]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w10_qp_12.pdf q8 ? And what's the general way of solving these kind of question where we have intermediates ?

 

[Hinafatima]

Can somebody help me to explain the way of quoting the link please?

 

[My Name]

plz can anyone post good notes of physical chemistry especially bond angles, sp3 hybridization etc??

Have you tried any youtube videos?
I think they'll help.

 

[Dark Destination]

Can somebody help me to explain the way of quoting the link please?

You have to open the past paper in a new tab, and click on the address bar, and copy the link from there. Then you paste it here.

 

[Fate0]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_12.pdf q8 ? And what's the general way of solving these kind of question where we have intermediates ?

The enthalphy change of formation hydrated calcium ions is this.
Ca(s) + aq – 2e– → Ca2+(aq)

So we need to go Ca2+ in the end.
We take Ca(s) and convert them to Ca(g) . Delta H = 177

Now comes the Data Booklet part.
We need to ionise this Ca(g).
First ionisation energy = 590
Second ionisation energy= 1150

Till now we have Ca 2+ (g)

We take that and convert to Ca2+ (aq) for which the energy is -1565.

Add all the energies. 177+590+1150-1565 = +352 which is (D)

In these questions just try to make connection and follow a route. Think about initial states and the final states and then solve it.