Chemistry: Post your doubts here!

[TANJIAHOU]

oh i thought since concentration of PbCl2 was lesser than 1 moldm-3, the equilibrium will shift to the left, making Ep more negative.

 

[itallion stallion]

oh i thought since concentration of PbCl2 was lesser than 1 moldm-3, the equilibrium will shift to the left, making Ep more negative.

Shifting to left won't make it more positive?
It was Pb+2+2e gives Pb so Pb concentration less will cause the reaction to go In backward direction making Eo positive,that's what i thought.

 

[TANJIAHOU]

Pb2+ + 2e ---> Pb -0.14v
If shift to left, should be less positive?

 

[BeBeskii108]

My lattice energy was positive 2242 something like that ? is my answer wrong ?

 

[TANJIAHOU]

it is always negative... I got -2242KJmol-1

 

[BeBeskii108]

it is always negative... I got -2242KJmol-1

. I got +2242. I hope examiners would give me 2 out 3.

 

[omarjaved619]

I divided my lattice energy by 1000, not noticing its already in kJ

 

[itallion stallion]

Can someone tell is there any ecf mark in the graph of acid and NaOH?

 

[HarisShahzad]

For starters, Lattice Energy can be either positive or negative. Depending on wether youre talking about bond breaking or bond formation. However with reference to how the Born Haber Cycle was formed in that question, Lattice Energy was exothermic.
Secondly, the electrode potential was -0.19V
Reason?
The reduction potential of 1 mol/dm3 was -0.13
Pb2+ + 2e <----> Pb -0.13V
Since the concentration is less than 1 mol/dm3, the equlibrium will shift to the left and think about it this way. It will be even more difficult to reduce so reduction potential will further decrease
Hence 0.19
Now for graph
first of all graph ended at 12.5. Final pH was 12.5
Inital ph was I think, if I remember correctly, 2.8
There would be a very small steep graph initally as the acid was weak
Then a buffer would be formed so slow rise in pH until 10 cm3
Steep vertical portion at 10 cm3
End point above 7
Finally pH would be 12.5
I found Question 1 Part 2 a little difficult
Didnt know what to write
Also the question where he converted -CONH2 to -CH2NH2
I thought about it
Hes reducing
So I just used LiAlH4, not NaBH4, since NaBH4 since it is weak. And I was right.

 

[HarisShahzad]

I had a couple of friends come out of the paper claiming paper was extremely easy and all that
They didnt even know that to prove that Sn and Pb react with oxidising and reducing agents differently, we had to quote Standard Electrode Potentials
They just wrote since the +4 oxides are less stable down group four and stuff
Paper was easy but only for those who knew syllabus inside out.
So dont be scared guys
GT wont be that high
There will be hardly any 'shocking' grades
If you did good
You will get your just reward

 

[unkidd]

my pH was coming as 11. How many marks will I lose. and can Sn and Hcl be used for reduction.

 

[HarisShahzad]

my pH was coming as 11. How many marks will I lose. and can Sn and Hcl be used for reduction.

Honestly, not quite sure
depends on where you made the mistake
ecf might get you marks
as for reducing agent
agreed Sn + HCl is a reducing agent
but im not someone you should be asking
I was as surprised as you are and checked LiAlH4 from the net

 

[itallion stallion]

Honestly, not quite sure
depends on where you made the mistake
ecf might get you marks
as for reducing agent
agreed Sn + HCl is a reducing agent
but im not someone you should be asking
I was as surprised as you are and checked LiAlH4 from the net

Can KI be used as a reducing agent in Sn reaction?

 

[unkidd]

What was the answer of Q3 optical isomers and ketones one.

 

[Rahma Abdelrahman]

Var

iant 41

Are you sure it was V1? Because I am sure that paper was TERRIBLE!

 

[Namehere]

Couldn´t we get a more difficult paper...? Paper 4 variant 1, my goodness... Will lose minimum 10-12 marks.

 

[AbbbbY]

I had a couple of friends come out of the paper claiming paper was extremely easy and all that
They didnt even know that to prove that Sn and Pb react with oxidising and reducing agents differently, we had to quote Standard Electrode Potentials
They just wrote since the +4 oxides are less stable down group four and stuff
Paper was easy but only for those who knew syllabus inside out.
So dont be scared guys
GT wont be that high
There will be hardly any 'shocking' grades
If you did good
You will get your just reward

By shocking, I meant, currently everyone I ask is already placing themselves at A* given the paper.

And yes. This was a common mistake. A lot of people couldn't tackle this question OR the part succeeded it, which asked for oxidation and reduction equations. Q1a was troublesome for a lot of people too, surprisingly. I'm not going to name the questions here for the 24 hour's sake.

Organic conditions messed with a lot of people, as did the last 2 parts of applications. But, all in all, IMO if someone had studied conceptually and not just by the past paper question types, it was a pretty easy paper.

 

[A star]

Can KI be used as a reducing agent in Sn reaction?

i used it too , it can be

 

[A star]

By shocking, I meant, currently everyone I ask is already placing themselves at A* given the paper.

And yes. This was a common mistake. A lot of people couldn't tackle this question OR the part succeeded it, which asked for oxidation and reduction equations. Q1a was troublesome for a lot of people too, surprisingly. I'm not going to name the questions here for the 24 hour's sake.

Organic conditions messed with a lot of people, as did the last 2 parts of applications. But, all in all, IMO if someone had studied conceptually and not just by the past paper question types, it was a pretty easy paper.

lol people had so many silly answers that made me laugh though. but it was atleast not difficult

 

[unkidd]

can someone after 24 hours write all the answers and explain me how we had to do the Ph question after 24 hours