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

1. Jan 11 paper was much easier i got 70% in it, shame it was a past paper and doesn't mean anything for me!!!!
2. it said time for paper on the board ...1.30pm-3.45pm
I spend like 2 mins trying to figure out that we had 2.15 hr for the exam..
and then half way through I realised that was for the dyslexics
3. Im guessing i got about 85 raw, maybe minus a lil bit, only got 1 mark of the 9 mark question and screwed up the polymer complex ion.. Other than that i cant say i found any of it very hard... I dont usually give a ****e about rep but it will be interesting to see if i get negged for daring to suggest i liked most of the paper, the magic tang made me laugh xD, i guessed because low pHs cause a sour taste so it is a valid prediction
4. the paper was hard!! Someone please create a facebook page for protest against it
5. (Original post by missred93)
I got 2nd order aswell, because it didnt have a constant half life --the time went from around 190 to 400 which means it hasnt doubled = no constant half life?

I may be wrong though?
Im afraid 190 = 200 (1 significant figure) 400-200 = 200. 600 - 400 = 200.

all is 200 therefore constant half life, therefore order is 1.

half life = time it takes for conc of reactant to reduce by half. (time it takes, therefore the second half life is 400-200 = 200, not just 400) anyway you might get error carried forward mark and working out mark. good luck
6. (Original post by Vidja)
From the textbook:
"A first order reaction can easily be identified from a concentration time graph. a first order reaction has a constant half life"

The half lives were 190 then 210.

Nowhere in the specification does it say "Half life is constant except sometimes when it's almost constant. It's still first order then."

The half life was increasing. If the mark scheme only gives a mark for first order then that is ridiculous.
I measured the half-life a third time and it was 190s again, so I don't think it could have been second order.
If it were second order, the half-life should've doubled I think.
7. I cant even discuss answers with you guys......I couldnt even attempt half of them
8. (Original post by Krgood2309)
it also went back down to 200 after though.

absolutely rancid paper. ocr are pulling them out this year.
well it does not say that if a half life is changing then constant then bla bla bla in the book. Maybe this is another impossible question like the ones weve been seein on the news.

OCR = Oxford + Cambridge. Feel sorry for thier students now. they have no idea of what is going to hit them.
9. OHHHH dear!!! i think i've screwed this up big time.
For the hydration enthaply Mg i got -1613
for Kc I got 101.3 dm3 mol-1
For Br I got first order. Didnt have a clue how to find initial rate of reaction and ended up getting a K value of 1. s-1
I got 2.1 for pH looks like something was right.
-58 for (delta)G
and i got 6.8% purity and realised as i walked out of the exam i forgot to times it by 10 for 250cm3

goodbye university of bristol.... goodbye future..... hello depression, binge eating & obesity
10. (Original post by Jtking3000)
-1921 (you had to double the hydration enthalpy for cl-)
This, though i dont really remember my value for it

Ppl who used lactic acid what was your salt acid ratio?
11. (Original post by missred93)
I got 2nd order aswell, because it didnt have a constant half life --the time went from around 190 to 400 which means it hasnt doubled = no constant half life?

I may be wrong though?
yeh but its almostt doubled...since there was a line of best fit i assumed it would be approximate anyway so i said 1st order...argh this paper was REVOLTING
12. (Original post by Vidja)
From the textbook:
"A first order reaction can easily be identified from a concentration time graph. a first order reaction has a constant half life"

The half lives were 190 then 210.

Nowhere in the specification does it say "Half life is constant except sometimes when it's almost constant. It's still first order then."

The half life was increasing. If the mark scheme only gives a mark for first order then that is ridiculous.
If you worked out more than 2 half lives, then they oscillated around the 200 s value. I got something like 190, 210, when going from the start concentration, halving it, halving again etc. And also checked, 0.004 --> 0.002 --> 0.001 (I think?) and they all came out as around 200. Allowing for experimental inaccuracy, the half life was constant. Also, the shape of the curve was the same as that of an exponential graph, it's slightly less steep than for a second order curve. Pretty sure it was first order.
13. what was the born harbour cycle about again
14. Did anyone get 67.8% for the last one? I'm pretty sure thats right!
15. (Original post by Sereni)
This, though i dont really remember my value for it

Ppl who used lactic acid what was your salt acid ratio?
0.49
16. (Original post by CeliaG593)
OHHHH dear!!! i think i've screwed this up big time.
For the hydration enthaply Mg i got -1613
for Kc I got 101.3 dm3 mol-1
For Br I got first order. Didnt have a clue how to find initial rate of reaction and ended up getting a K value of 1. s-1
I got 2.1 for pH looks like something was right.
-58 for (delta)G
and i got 6.8% purity and realised as i walked out of the exam i forgot to times it by 10 for 250cm3

goodbye university of bristol.... goodbye future..... hello depression, binge eating &amp; obesity
I thought it was horrific
also got 2.1 for pH
and 6.8% for purity as I forgot to x10
overall thought it was a really really hard paper
17. i hope Hogwarts will still take me in
18. half life was constant ..i got 190 first then 200 , then 200 then 200 so I assumed it was 200 (s) and then I got 1st order Br2 and then I just did rate = k[Br2] and subsituted values from the graph to find K... thats wrong isnt it???
19. i swear the OCR guys this year must've been high when they wrote their papers. Hedgehogs and seaweed eating sheep in biology and now we've got willy wonka in chemistry with his magic tangy sweets.
what next eh.
:P
20. Guys lets make the Unofficial Mark Scheme Mk1
Please say if you have things to add, modify, or correct (theres lots!)

?)definition of lattice enthalpy: Energy given out when one mole of an ionic compound is formed from its constituent gaseous ions.[2]
?)Why is hydration enthalpy for Cl- exothermic? Bonds formed with deltaH+ on water molecules, heat given out.
?)Born Haber diagram of Enthalpy of solution, hydration, lattice enthalpy. 4 stages, incomplete answers: Mg2+(g) + 2Cl-(aq), Mg2+(aq) + 2Cl-(aq) [2]
?)Enthalpy of hydration for Mg2+ = summin like -1700ish kJmol-1?
?)[Br] graph question. Marks for calculating 3 half lives, ~200s, stating that constant half life means its 1st order. State that methanoic acid in excess, so [methanoic] is constant and can be disregarded in the rate equation. calculate k by working out the gradient of tangent at t=0, answer and units= ?? s^-1
?)
?)
?)Kc = 45
?)Strength of acids question: Strength is measure of degree of dissociation of acid in aqeous solution. Stronger acid: more dissociation.
?)Magic tang question: use lactic acid because its pKa is close to our desired pH (within one unit), so it buffers better. I used henderson hasselbach equation, pKa = pH + log [A-]/[HA] or you can use the ka expression to work out [A-]/[HA], which (I got) ~0.49
I think it will be tangy because the buffering range (+/- 1 pH unit of pKa) certainly ecompasses the tangy pH of 3.55
?)
?)
?)
?)
?)
?)monomer unit for the complex ion polymer

?)

?)

?)

?)

?)

?) % of Cu in Brass question
Equations with state symbols:
Cu (s) + 4HNO3 (l) --> Cu(NO3)2 (aq) + 2NO3- (aq) + 2NO + 2H2O
Cu2+ + 2I- (aq) --> CuI (s) + 0.5 I2 (aq)
(one more which i can't rememebr)
n(Cu) = 0.5n(I2) = n(S2O3)
titre of 24.98 x 10^-3 cm^3 or summin, 0.1moldm^-3, n (S2O3)=that, so n(Cu) = 24.98 x 10^-3 cm^3
so m(Cu) = nM = 24.98 x 10^-3 * 63.5 = 1.59 g of Cu in 2.8g or summin brass.
% by mass= 67 point something percent, it asked to 1dp.

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