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

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Reply 1960

RodrigoB

WHAT WAS THE ACID those bastards chemists used to produce the candy stuff ?

Reply 1961

charlene_lamm

Original post by Lissa-154

Anyone thinking of complaining to OCR again? :')

gotta revise for tmr's Maths C3.. and m already fed up with OCR..

Reply 1962

786girl

Original post by Sceaga

did everyone else get -108 for the gibbs question?

yeh so did that mean it was NOT spontaneous???? arghh how did u have 2 do it?
i worked out delta S from the given data
then used it to find gibbs
was that the right method?? omg i lost about 30 marks just like that
i faileddddddddddd

Reply 1963

hiyarearl

Original post by Jtking3000

Anyone else get around 5x10^-3 s^-1 for the rate?

No I got 3x10^-3 s^-1 but I messed up the order because I was panicking due to how hard the rest of the paper was. :mad:

I need an A overall in chemistry and I've hit high A's for every paper so far but I thought that was SOOO bad it was stupid. I just found the paper demoralising and confusing. I need a D grade absolute minimum to get an A grade, if I have not got that it will be a bloody joke.

I can't even tell how I've done. On one hand I could have done well if the grade boundaries are low but if they are medium-high I will have failed epicly. Did the Jan 2011 paper this morning and got an easy A grade on it and found it pretty straight forward but found this 100 times harder. Feel robbed, that was so unfair.

Reply 1964

student777

Original post by Student21

I put enthalpy positive cos its endothermic and entropy negative as solid to liquid is more disordered. Am i right?

You're right, but entropy should be positive as it is becoming more disordered.

Reply 1965

SaturnineDragonfly

Original post by jontylol

Was there an actual method to working out which acid to use for the 'magic tang'? Because i said that all the acids would work so i just picked lactic acid and went with it :/ And i got a 1:2 ratio of salt:acid

It was quite strange, usually there's some obvious thread to pick up to deduce they tell you to, but I also found that in that question there seemed to be no evident reason to choose any of the acids. I chose lactic acid as well, since the sweet has to be edible at least, so it seemed to me that the only two possibilities were lactic and ethanoic, as I doubt it's healthy to eat the acid with benzene in it (can't remember it's actual name) and pyruvic. And out of lactic acid and ethanoic acid, lactic had the lower pKa value, so was a stronger acid (and the pH had to be low, 3.55). That's the only line of reasoning I could think of. Any one else have any other reasoning or figure it out differently for some subtle reason? :confused:

Although, thinking about it, pyruvic is possibly edible? I really don't know.

(edited 12 years ago)

Reply 1966

Vidja

Original post by susan23

i put enthalp was negative because temperature was 0 making S xT = 0 so the only way G could be less than 1 for feasability was if delta-H was negative?!??!

OMG nooooo thats probably the only thing i thought I got right!?!!?!?

Temperature was 0 celcius I'm afraid. You use kelvin, so it's 273

Reply 1967

J DOT A

The rate was like 0.00006 something wasnt it? I honestly can't remeber.

Reply 1968

Vidja

Original post by 786girl

If Delta G is less than zero the reaction is spontaneous
108<0 so it WAS spontaneus.

Reply 1969

Jambo_100

Original post by RodrigoB

SAME situation mate

I WAS supposed to be doing great on this chem papers
but so far I am flopping like ****

FUTURE CHEMICAL ENGINEER DEGREE = FAIL

Same here! :-(

Reply 1970

BackDoorEntry

Original post by Jtking3000

Anyone else get around 5x10^-3 s^-1 for the rate?

i got 4x10^-3 s^-1 using a tangent at t=0

That paper absolutely killed me! Miles harder than both past papers combined, squared, and cubed.

The last question i got 3.4%, i think i left out a 0 somewhere. This is horrible!

Reply 1971

Killmepls

Am I the only one who thinks this was much harder than Jan and June last year? 65% for an A it was in January I'm hoping for about 60% this time...

Reply 1972

susan23

Email: [email protected]
Tel: 01223 553998
Fax: 01223 552627

Reply 1973

Lissa-154

Original post by SaturnineDragonfly

It was quite strange, usually there's some obvious thread to pick up to deduce they tell you to, but I also found that in that question there seemed to be no evident reason to choose any of the acids. I chose lactic acid as well, since the sweet has to be edible at least, so it seemed to me that the only two possibilities were lactic and ethanoic, as I doubt it's healthy to eat the acid with benzene in it (can't remember it's actual name) and pyruvic. And out of lactic acid and ethanoic acid, lactic had the lower pKa value, so was a stronger acid. That's the only line of reasoning I could think of. Any one else have any other reasoning or figure it out differently for some subtle reason? :confused:

I chose lactic acid too because the pH value was similar to the pKa value, meaning that it would be a weak acid and since lactic acid is used in milk it might be a component of a sweet. :s idk, i had to rush this question at the very end because i had no idea at all D:

Reply 1974

786girl

why is ocr making our lives so hard this year !! Grrrrrrr

Reply 1975

GiraffePoacher

Original post by RodrigoB

WHAT WAS THE ACID those bastards chemists used to produce the candy stuff ?

I actually thought you could have picked any of them? Because I think the pH of the buffer depends more on the acid : salt proportions rather than the pH of the acid alone.

So for the sake of ease, I picked acetic (ethanoic) acid.

But I could be wrong.