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

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Reply 1620

Flint_09

Original post by SteveScott

Does pKa = pH?

nooooooooooooooo

pka= -logka

ka= 10^-pka

Reply 1621

ViralRiver

Original post by ViralRiver

Do we need to remember colours and oxidation states? What about redox equilibria such as MnO4 and Fe etc?

Reply 1622

gkaur123

Original post by SteveScott

Does pKa = pH?

pKa is basically just -log(Ka), its not pH.
the actual Ka calculation can be used to work out the pH if you work out the concentration of H+

Reply 1623

asem93

Original post by Flint_09

nooooooooooooooo

pka= -logka

ka= 10^-pka

hmmmmmm.....Are you sure?

Jokes :tongue:

Reply 1624

SteveScott

Original post by asem93

NO! NO! NO! :eek:

Haha

I know pKa = -logKa , so 10^-pKa = Ka

Ka = [H+][A-]/[HA]

but i thought i saw something about pka being equal to pH for weak acids.....I dunno.

Reply 1625

asem93

Original post by ViralRiver

Colours of common compounds

Reply 1626

FBPS

Good Luck Everyone!!

Lets just hope its an easy paper

Reply 1627

Perky perks

what are the cycles called that involve lattice enthalpy and enthalpy change of solution and do we have to know them??

Reply 1628

InsaneFandom

Do we need to know tetrahedral complex metal ions??

Reply 1629

SteveScott

Original post by Perky perks

what are the cycles called that involve lattice enthalpy and enthalpy change of solution and do we have to know them??

Yes

Born Haber cycles

It all depends on the reaction. If it gives a table, look at the enthalpy change values.

Reply 1630

asem93

Original post by Perky perks

what are the cycles called that involve lattice enthalpy and enthalpy change of solution and do we have to know them??

They are a form of Born Haber cycle, you can also argue a bit like Hess' Law

Reply 1631

susan23

Original post by 123trident

actually, I'm a bit confused on free enrgy feasiblity. Can someone go throug all the options explaining them, please?

a reaction is feasiable only if the free gibs energy G is less than zero (so negative value).
This can only happen if the enthalpy H is negative and the entropy S is positive
or when enthalpy is positive and entropy positive (reaction will take place at low temperatuures only) or when enthalpy is negative and entropy is also negative.

these combinations all should lead to G being less than zero and hence reactions are feasiable

LOL was that confusing? sorry

they all follow equation G=H - ST

Reply 1632

Flux_Pav

does the ionic radius decrease as you move from left to right of periodic table?

Reply 1633

hiyarearl

Just done Jan 2011, got 72/100 which was a comfortable A it seems.

Does anyone know what the raw mark was for 100% UMS for Jan 2011, out of interest? :smile:

Reply 1634

asem93

Original post by susan23

When delta G is less than 0 !!

Reply 1635

SteveScott

Original post by InsaneFandom

Do we need to know tetrahedral complex metal ions??

You need to know at least one of octohedral, tetrahedral and the flat one with four ligands, and at least one optical and stereoisomer, but I'd have thought two would be preferable.

Reply 1636

gkaur123

Original post by Perky perks

what are the cycles called that involve lattice enthalpy and enthalpy change of solution and do we have to know them??

they are another type of born-haber cycle, and yep i think we do need to know them.

Reply 1637

vrm

GOOD LUCK PEOPLE.... hopefully we get a good paper....

Reply 1638

SteveScott

Original post by hiyarearl

Just done Jan 2011, got 72/100 which was a comfortable A it seems.

Does anyone know what the raw mark was for 100% UMS for Jan 2011, out of interest? :smile:

Is that on the internet?

Reply 1639

asem93

Original post by hiyarearl

Just done Jan 2011, got 72/100 which was a comfortable A it seems.

Does anyone know what the raw mark was for 100% UMS for Jan 2011, out of interest? :smile:

80

And believe it or not I got 72 as well!