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

Has the mark scheme for the jan 2011 paper been posted by any chance? :P

The rate equation gives you the reactants and the molar quantities (look at the power of each reactant concentrations) involved in one step (the rate - determining step) of the reaction. I don't think there's any specific rule that it has to be the first step but I think it's decent practice to put it down as the first.

[[Fe(H20)6]2+] over [Fe2+]

sorry, I don't know why I included H20 the first time. sorry for any confusion caused.

just did the 2011 jan paper and got 78 but the only reason i am happy is BECAUSE I FINALLY KNOW HOW TO DO REDOX EQUATIONS
HIP HIP HURAY!!!!

i am however gonna "ignore" any questions on enthalpy of solution/hydration .... dont get it!

good luck everyone!!
lool imagine if we get another hair perm style question. haha fingers crossed its a lovely paper!!!!!

Okay. But is it like the product/s of the 1st step are the reactants in the second step which react to form the overall product of the reaction? I'm confused

I'd begin by writing down all of the reactants/products that you're given in the question, aside from any hydroxide ions, protons or H20 that you may well need to even things up - so, begin with saying that N02 + I- goes to I2 + NO
Then, you need to work out which of these atoms change oxidation number, and balance those atmos that do (so, I goes from -1 to 0 so balance the number of iodines). That should set you on your way

so would the answer be ...:

H20 +I2 + NO2 - -----> NO + 2I- + 2OH-

any main things to keep in mind on buffer questions?

exo is making bonds -Ve
endo is breaking bonds +Ve

ex-girlfriend makes bitches negative
enormous butt is breaking positive

LOL thats soooo crap....ahhahahahahaah
so sorry about that they dont even make sense

any main things to keep in mind on buffer questions?

afraid not the atoms balance but the charges don't - look more closely at how n changes its oxidation number

does n go from 3+ to 2+??

- made from weak acid and salt of a weak acid.

- uses equilibrium (ha ---> h^+ + a^-) to minimise ph changes

- when h^+ is added to the buffer solution it reacts with the conjugate base a^- and the position of equilibrium shifts to the left removing the added h^+ ions.

- when oh^- is added to the buffer solution it reacts with a small concentration of h^+ ions (h^+ + oh^- ---> h2o). Ha (weak acid) dissociates and the equilibrium shifts to the right restoring the h^+ ions that reacted.

^ that's the most important stuff.