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

1. (Original post by hey-hey-hey)
Ahh thats good too,
ahh im jealous i wish i could play that instrument, Ukalali? something aha i cant spell :/
im gonna buy one so i cann learn all summer sooo happy http://www.youtube.com/watch?v=ZCcVg3b4ZRk
2. (Original post by goldlock)
I reckon a question'll come up that asks for the pH of a buffer, the main thing to bear in mind being that the concentration of the base doesn't equal the conc. of H+, the carbonic acid hydrogencarbonate stuff too, that'll probably show.
Why cant the conc of the the base be equal to the H+, because it would not produce enough A- ions? So does the base have to be higher/lower:/
3. (Original post by bambinooo)
im gonna buy one so i cann learn all summer sooo happy http://www.youtube.com/watch?v=ZCcVg3b4ZRk
Me too!! ahaa it'll be a nice achievement
4. (Original post by hey-hey-hey)
Why cant the conc of the the base be equal to the H+, because it would not produce enough A- ions? So does the base have to be higher/lower:/
That's why we need a buffer solution instead of just a plain old weak acid, yeah, the acid barely dissociates so the concs. of H+ and A- would be very low (and equal) - using a salt of the weak acid means that in solution, it dissociates completely, releasing lots of A- so overall the buffer has lots of HA, a little H+ and a lot of A-, and we need a lot of A- for the buffer to function (page 150 of the textbook has a really handy diagram which'll clarify it!)
5. (Original post by bambinooo)
yes please ....
First of all, you work out what you can - so looking at the mess we've been given, you can see that we have masses of CO2 and H20, so we can work out their moles. also, they say that we burn the eugenol in oxygen so we can make an equation: Weugenol + XO2 goes to YCO2 + ZH20. Now after you work out the moles of water and co2, you can also get the moles of eugenol since you have its mass and it's m/z value - when you have all of these molar quantities, you can fill them in the equation - see where we go from there
6. (Original post by bambinooo)
im gonna buy one so i cann learn all summer sooo happy http://www.youtube.com/watch?v=ZCcVg3b4ZRk
thanks 4 + rep, just gave u one..
7. Explain why the first electron affinity for oxygen is exothermic.?! 1 mark

MS is quite rubbish! just says experiencing attraction from nucleus
I thought its because of bonds being made between outer e and nucleus !!
Someone help me out on this +rep

"GOLDlock" Accidentally +rep u for the 2nd time
8. (Original post by goldlock)
That's why we need a buffer solution instead of just a plain old weak acid, yeah, the acid barely dissociates so the concs. of H+ and A- would be very low (and equal) - using a salt of the weak acid means that in solution, it dissociates completely, releasing lots of A- so overall the buffer has lots of HA, a little H+ and a lot of A-, and we need a lot of A- for the buffer to function (page 150 of the textbook has a really handy diagram which'll clarify it!)
Ahhh right..thanks
Bet ur gana get A*
I'm off, im so tired! literally falling asleep on my desk aha
Good luck!
9. Gooood luuuuuuuuuckkkkkkkkkkkk guuuuuuuuyssssss :d
10. (Original post by arvin_infinity)
Explain why the first electron affinity for oxygen is exothermic.?! 1 mark

MS is quite rubbish! just says experiencing attraction from nucleus
I thought its because of bonds being made between outer e and nucleus !!
Someone help me out on this +rep
I think it's a bit of a murky one since I'm not sure if there's an actual "bond" - I'd say it's exothermic because the electron you're adding is being attracted in by the nucleus, I suppose for one mark that's all you'd need but I agree with your reason
11. (Original post by goldlock)
First of all, you work out what you can - so looking at the mess we've been given, you can see that we have masses of CO2 and H20, so we can work out their moles. also, they say that we burn the eugenol in oxygen so we can make an equation: Weugenol + XO2 goes to YCO2 + ZH20. Now after you work out the moles of water and co2, you can also get the moles of eugenol since you have its mass and it's m/z value - when you have all of these molar quantities, you can fill them in the equation - see where we go from there
but didnt they want us to give molecular formula?? can we do that from knowing w?
also why do we add to make a buffer we add excess acid? (to both an alkali or conjuate base)...but why? is it because the acid only partially dissociates and you want to obtain a large resivoir of weak acid? thanks
12. (Original post by hey-hey-hey)
Ahhh right..thanks
Bet ur gana get A*
I'm off, im so tired! literally falling asleep on my desk aha
Good luck!
Lol I wish, haven't even managed over 90 in a single chem. exam so far :/ still going for it though! Good luck to you too
13. (Original post by arvin_infinity)
Explain why the first electron affinity for oxygen is exothermic.?! 1 mark

MS is quite rubbish! just says experiencing attraction from nucleus
I thought its because of bonds being made between outer e and nucleus !!
Someone help me out on this +rep

"GOLDlock" Accidentally +rep u for the 2nd time
1st EA is exothermic because the electron is attracted to the outer shell of the atom by the nucleus showing an exothermic process.
14. whats the difference between standard enthalpy change of solution and standard enthalpy change of hydration?
15. (Original post by susan23)
1st EA is exothermic because the electron is attracted to the outer shell of the atom by the nucleus showing an exothermic process.
Well ..its best to just remember it but its not really convincing to say attraction releases energy !
16. (Original post by susan23)
whats the difference between standard enthalpy change of solution and standard enthalpy change of hydration?
enthalphy change of hydration is one of the two components that, when you add together, give enthalphy of solution - the solution enthalphy is the enthalphy change for the whole process of dissolving of a compound, the hydration enthalphy is the enthalpy change that happens when 1 mole of isolated gaseous ions dissolves to form 1 mole of aqueous ions
17. (Original post by susan23)
whats the difference between standard enthalpy change of solution and standard enthalpy change of hydration?
standard enthalpy change of sol is the enthalpy change that takes place when i mol of an compound (i.e. ionic solid) is completely dissolved in water wheras the enthalpy change of hyd refers to the enthalpy change that takes place when one mole of isolated gaseous ions dissolves in water forming one mole of aqueous ions under standard conditions :

Hsol = Hhyd-Hle

H= DELTA H

think of it as a triangle so from solid to gas to aqueous ----and sold to aqueous is the Hsol!
18. I think it's only us 4 who are awake loooool
19. (Original post by susan23)
I think it's only us 4 who are awake loooool
Heh - I'm glad the exam's in the afternoon, I'm not a morning person!
20. (Original post by goldlock)
Heh - I'm glad the exam's in the afternoon, I'm not a morning person!
same! I suffer from memory loss and insomnia so night time revision is great lol

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