Chemistry Paper 4-theory- doubts =D

[knowitall10]

we've decided that the past paper doubts will be discussed here and the conceptual doubts in chem and phy in xhizors 's thread, i'll tag u there as well

 

[knowitall10]

https://www.xtremepapers.com/commun...epoints-ondemandonly.25941/page-8#post-537135
The link to Brother xhizors 's thread

 

[knowitall10]

Thank you knowitall10

Anyway, I'll repost:
In questions such as these:
"Explain why barium sulphate is less soluble than calcium sulphate"

The ms says:
down the group: the ∆Hsolution becomes more endothermic;
both lattice energy and ∆Hhydration become less (exothermic);
due to ionic radius (of M2+) increasing;
but ∆Hhydration changes more than lattice energy


Can someone please explain this to me?

Sure)
Barium is lower than Calcium in the Periodic table yeah?
and we also know that as you go down the group, ionic raadius increases, see:
Mg2+ > Ca2+ > Sr2+ >Ba2+
Larger ions have lower enthalpy changes of hydration: Ba2+ is larger than Ca2+ Hydration enthalpy decreases down the gp.
Same is the order of Lattic Enthalpy: Lattice energy is lesser if ions are large. therefore, lattice enthalpy decreases down the group.
Now, remember:
- Lattice energy gets less exo down the gp.
- Hydration enthalpy gets less exo down the gp
-so applying Hess's Law: Enthaloy change of solution gets more endo down the gp.
the solubility of gp 2 sulfates decreases down the gp.
Please do let me knw if u dnt get it

 

[knowitall10]

Btw, brother Ashique which book are u using? It explains it pretty well in there... if u don't have it, let me know, i'll upload the photos of those pgs

 

[lavanyamane]

Look, my friend, you can do it either way, when u reverse the signs (which happens when u reverse the equation), you simply add all of them.
Another way is, you don
t reverse the signs and then you use the {E more +ve - E less +ve}... now? do u get it?

Perfect, thank you!

 

[knowitall10]

Perfect, thank you!

No problem

 

[lavanyamane]

Ariel Robert
brother, i'm assuming ur using the same book as mine cz ur in Jeddah, can u please answer qnother question?
Look at page 278 of our txtbk, fig 19.12? Can u please tell me how to figure out the half equation of the half cell on the left hand side?
btw, @everyone who has the same txtbk

Hey there, I use the same book and even though this might have been answered, here it is: the electrode potential is simply the voltmeter reading (+1.52 V) because that of the standard hydrogen half-cell = 0V

 

[knowitall10]

Hey there, I use the same book and even though this might have been answered, here it is: the electrode potential is simply the voltmeter reading (+1.52 V) because that of the standard hydrogen half-cell = 0V

Heyy
Thanks! That was simple!

 

[lionkill3r]

a tip regarding electro chemistry:
The electrode potential value is always same for a reaction ( ina given direction ) no matter how yu balance it !
0.5I2 + e- = I- value is +0.54V
and for I2 + 2e- = 2I- value is still 0.54v !!!

 

[knowitall10]

a tip regarding electro chemistry:
The electrode potential value is always same for a reaction ( ina given direction ) no matter how yu balance it !
0.5I2 + e- = I- value is +0.54V
and for I2 + 2e- = 2I- value is still 0.54v !!!

Cool........................

 

[railey]

Hello people. Salaam alykum,
How did you guys revise for applications, did you read the booklet?
Cause it has soo much information that is unnecessary!

 

[lionkill3r]

Hello people. Salaam alykum,
How did you guys revise for applications, did you read the booklet?
Cause it has soo much information that is unnecessary!

I do biology so electrophoreses, proteins and stuff get covered. In physics NMR principles get covered ( not identification ) but as for rest i read the text book. I do not have any notes on nanotechnology! For Polymers i read the text book.
What you said is tru the application booklet has too much unnecessary information !

 

[railey]

I do biology so electrophoreses, proteins and stuff get covered. In physics NMR principles get covered ( not identification ) but as for rest i read the text book. I do not have any notes on nanotechnology! For Polymers i read the text book.
What you said is tru the application booklet has too much unnecessary information !

I do Biology so the first app topic on DNA and all is fine, same with electrophoresis but the Mass spectra and NMR i need to do. I would suggest using www.chemguide.co.uk/cie.

 

[railey]

S/a once again.
Can anyone please help me with NMR. I don't get the part in the apps booklet when it talks about the difference in the energies and the 'spin +1/2 aligned' and the 'spin-1/2 opposed' and the Planck equation. It makes no sense to me AT ALL!

 

[knowitall10]

S/a once again.
Can anyone please help me with NMR. I don't get the part in the apps booklet when it talks about the difference in the energies and the 'spin +1/2 aligned' and the 'spin-1/2 opposed' and the Planck equation. It makes no sense to me AT ALL!

https://www.xtremepapers.com/commun...-some-keypoints-notepoints-ondemandonly.25941
Look at the first two pages of Xhizors's thread-Chem and phy doubts i think.... he explains it pretty well.

 

[railey]

https://www.xtremepapers.com/commun...-some-keypoints-notepoints-ondemandonly.25941
Look at the first two pages of Xhizors's thread-Chem and phy doubts i think.... he explains it pretty well.

I don't see. They are talking about peaks, i want to know about the other NMR, like the introduction.

 

[lionkill3r]

I don't see. They are talking about peaks, i want to know about the other NMR, like the introduction.

If yu are doing physics the intro will be much easier.
Some nuclei have a property call spin that makes it behave like a tiny magnet. When such nuclei are placed in a large magnetic field, the nuclei precess ( that is line up along magnetic field) in two spin states (parallel and anti parallel). The energy gap between spin states is in radio freuqency range. So when radio frequency pulses (in physics yu need to say at larmor frequency) are emitted to the nuclei , the nuclei in lower energy state absorb energy and spin as the nuclei in higher energy state. The energy needed differs due to chemical environment. Hydrogen is the nuclei that spins or something like that

 

[railey]

If yu are doing physics the intro will be much easier.
Some nuclei have a property call spin that makes it behave like a tiny magnet. When such nuclei are placed in a large magnetic field, the nuclei precess ( that is line up along magnetic field) in two spin states (parallel and anti parallel). The energy gap between spin states is in radio freuqency range. So when radio frequency pulses (in physics yu need to say at larmor frequency) are emitted to the nuclei , the nuclei in lower energy state absorb energy and spin as the nuclei in higher energy state. The energy needed differs due to chemical environment. Hydrogen is the nuclei that spins or something like that

Oh okay.. I it makes sense a little. And i thank God i don't do physics. Btw have you seen any questions on this topic.. Like not to identify the compound present, but like on this introduction part?

 

[lionkill3r]

Yes
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w07_qp_4.pdf

Question number 9 (a)

 

[railey]

Yes
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w07_qp_4.pdf

Question number 9 (a)

Cool thanks.
Shukran