Equilibria, Energetics and Elements (F325) - June 2011 Exam.

Woah, just did the Jan 2011 F325 just to see abouts where I am... the paper was a bitch
so much so that 65% was an A, I got 76% I wonder what UMS that would give me,

Reply 62

J DOT A

Guys, can someone tell me what a Buffer is and how you make one with NH3 in one solution, and its conjugate acid in the other.

And what would happen if you added OH- and H+, where would the position of Eqm lie?

Reply 63

Original post by J DOT A

Guys, can someone tell me what a Buffer is and how you make one with NH3 in one solution, and its conjugate acid in the other.

And what would happen if you added OH- and H+, where would the position of Eqm lie?

Hey man,
Okay so remember that NH3(aq) is a weak base... so lets say CH3COOH is our weak acid to make a buffer solution using these two:

CH3COOH <-> CH3COO- (conjugate base) + H^+

CH3COOH + NH3 --> CH3COO- (conjugate base) + NH4^+

The first equation holds the key to the equilibrium:
adding H+ will increase the concentration of the reactants, more H+ will react with the conjugate base to form CH3COOH so equilibrium shifts to the left.

Now adding OH-:
OH- + H+ --> H20

This means the concentration of the reactants (H+) will be reduced causing a shift in the equilibrium to the right.

Hope that made sense!
Haydn

Reply 64

J DOT A

Original post by haydyb123

Hey man,
Okay so remember that NH3(aq) is a weak base... so lets say CH3COOH is our weak acid to make a buffer solution using these two:

CH3COOH <-> CH3COO- (conjugate base) + H^+

CH3COOH + NH3 --> CH3COO- (conjugate base) + NH4^+

The first equation holds the key to the equilibrium:
adding H+ will increase the concentration of the reactants, more H+ will react with the conjugate base to form CH3COOH so equilibrium shifts to the left.

Now adding OH-:
OH- + H+ --> H20

This means the concentration of the reactants (H+) will be reduced causing a shift in the equilibrium to the right.

Hope that made sense!
Haydn

Hmm

I thought that if we had NH3 as our base, the conjugate acid had to be weak and the salt of that acid also.
For example NH3, and Nh4Cl.

And then you add NH3+h20 AND then Nh4cl into h20?

Reply 65

Original post by J DOT A

Hmm

I thought that if we had NH3 as our base, the conjugate acid had to be weak and the salt of that acid also.
For example NH3, and Nh4Cl.

And then you add NH3+h20 AND then Nh4cl into h20?

First point: Your point is valid, but essentially all that happens is that the salt dissolves, which is why you have such a vast amount of conjugate base.

Second point: Technically speaking the salt is CH3COO-NH4+ but because it just dissolves in solution into CH3COO- + NH4+

and your final point:

Those are all possibilities, I thought that it was just if you add any source of H+ and OH- the outcomes are the same.

Reply 66

Original post by INeedToRevise

Isn't that F324?
The organic chem exam?

Yep im re-sitting F324 and AS Chains, F322 i think. Speaking of which, the exam for F322.. in a month!!! This is so depressing lol

Reply 67

Original post by haydyb123

Woah, just did the Jan 2011 F325 just to see abouts where I am... the paper was a bitch
so much so that 65% was an A, I got 76% I wonder what UMS that would give me,

76% sounds good, especially if that paper was bad. Hmmm i see a pattern. Our january F324 paper was bad too and so was F325. Do you think the re-sit paper for F324 and JUNE f325 will be easier?

Reply 68

Original post by Rosi M

76% sounds good, especially if that paper was bad. Hmmm i see a pattern. Our january F324 paper was bad too and so was F325. Do you think the re-sit paper for F324 and JUNE f325 will be easier?

Don't bank on it :wink:

when do they ever make it easy for us?

Reply 69

INeedToRevise

8

Original post by Rosi M

Yep im re-sitting F324 and AS Chains, F322 i think. Speaking of which, the exam for F322.. in a month!!! This is so depressing lol

I did F322 as a re-sit in January. It wasn't too bad tbh. I got an A- made up for my really bad grade in F324 haha. All the same questions keep coming up.

Original post by haydyb123

Don't bank on it :wink:

when do they ever make it easy for us?

So true.

Reply 70

Original post by haydyb123

Don't bank on it :wink:

when do they ever make it easy for us?

Hmmm true true. Sometimes they feel generous. I do the same board for biology too and in my opinion, they were feeling really nice then.

Reply 71

Original post by INeedToRevise

I did F322 as a re-sit in January. It wasn't too bad tbh. I got an A- made up for my really bad grade in F324 haha. All the same questions keep coming up.

So true.

Haha thats good! :smile:

Any tips? Alot of the content overlaps so it feels a 100 times easier now but still.

Reply 72

INeedToRevise

8

Original post by Rosi M

Haha thats good! :smile:

Any tips? Alot of the content overlaps so it feels a 100 times easier now but still.

Yeah. I think doing F324 helped for this. All I did was run through the content pretty quickly. I think I spent the most time on energy/ozone layer rubbish. And then I just did past papers, literally everything from the old spec and all the new spec aswell. And the examination questions in the book.
Some of the questions, I literally just learnt from the markscheme e.g. adsorbtion. Its like 4 marks and its so easy just to learn the answer.
Hope this helps you :smile:

Oh and thanks :smile:

(edited 13 years ago)

Reply 73

786girl

ive finished learning the content and am doing all the old syllabus questions...
dont ask what im doing up at 5 am.. my sleeping pattern is so messed up!

anyways please can someone explain to me in the nicest/simplest way possible.. how do u answer question 6 b) ii) on the JAN 2011 paper?? its a redox equation i dont get ittt helppppp!

Reply 74

786girl

btw what did u all get for ur coursework?i got 32/40 ! im so mad i could have done much better, now i need to make up for those marks in this exam lol

Reply 75

Original post by 786girl

ive finished learning the content and am doing all the old syllabus questions...
dont ask what im doing up at 5 am.. my sleeping pattern is so messed up!

anyways please can someone explain to me in the nicest/simplest way possible.. how do u answer question 6 b) ii) on the JAN 2011 paper?? its a redox equation i dont get ittt helppppp!

Do you mean 7b ii?
And if you did, I didn't get the right answer. You needed to get the previous question right on the colourless gas to have a hope in hell of getting it right!

Reply 76

sportycricketer

What I personally feel is that this module is "slightly easier" in the sense that the content isn't too hard and quite a bit of logical Arithmetic and Maths involved which is always good. The only problem is that the paper itself never tests your knowledge like in Biology, it's basically the application of your knowledge. Say you had to know an equation or a particular way to work out a question.
They then later put that theory into a much greater/difficult situation and test it then and therefore it's quite difficult to revise for it.
Another thing is the unpredictable mark scheme, which has been soo inconsistent over the years that you dont know what to put in your answer. I suppose Past papers is the way forward. Some part of me is ok with it but the application part is still haunting me

I would be happy to help anyone but I need someone, please, to explain me the feasibility of the half cells and equations where if one species can "oxidise" or "reduce" the other

Reply 77

Right Guard 3.D

13

I'm yet to do a past paper, still making brief notes and re-learning some stuff from the specification.

I got 36/40 for my practicals, considering last year I got 27/40 and couldn't improve I couldn't ask for better :smile:

Reply 78

Schoolio93