[Bi0logical]

When converting from Ka to pKa
do you just -log the Ka?
so e.g Ka= 5.0 x10^-3
pKa = -log 5.0 x10^-3 = 2.30

and would going from pKa to Ka just be shift-log ? (inverse log or whatever)

[Cleoleo]

(Original post by Toshiya)
Anyone think we'll get asked how gas-liquid chromatography works? I haven't seen a question on explaining how it works in any of the new spec papers. I kinda hope it doesn't, I have no idea how to explain it!

I would hacve thought you just need to mention stationary phase which is the high boiling liquid on a finely divided solid support, mobile phase which is the inert N2 gas and how it moves through and if the gas has a high affinity for the stationary phase, retention time is longer and if it is attracted more to the inert gas, then retention time will be less. The retention time is the time it takes for it to move through the oven and be detected. Then look up the retention time to identify the compound ?

[Bi0logical]

(Original post by Cleoleo)
S02 ... 2 bonds and 1 lone pair... what shape is this? Bond angle would be 120 right?

Does SO2 have 2 double bonds? or one?
O=S=O or O=S-O


Edit; either way there are three areas of electron density (the bonding pairs and the lone pair on the top of S) so = 120?

[bertiejess]

(Original post by Bi0logical)
When converting from Ka to pKa
do you just -log the Ka?
so e.g Ka= 5.0 x10^-3
pKa = -log 5.0 x10^-3 = 2.30

and would going from pKa to Ka just be shift-log ? (inverse log or whatever)

I think so

[cli121]

(Original post by Toshiya)
Anyone think we'll get asked how gas-liquid chromatography works? I haven't seen a question on explaining how it works in any of the new spec papers. I kinda hope it doesn't, I have no idea how to explain it!

mobile phase = unreactive carrier gas
stationary phase = viscous liquid (coats inside of tube)
the sample to be analysed is injected into the stream of carrier gas,ich carries it through the tube and over the stationary phase
compone of mixture constantly dissolve in the stationary phase, evapourates into mobile phase and then redissolves as they travel through
solubility of each component determines how long it spends dissolved in stationary phase.
high solubility = longer to travel

[Cleoleo]

(Original post by SimpleGirl)
Erm, methanol?

- C - O - H

The hydrogen on the end is attached to an oxygen. So, as splitting represents hydrogens on the adjacent carbon and this hydrogen isn't directly attached to a carbon atom, there is no splitting.

okk but would there be 2 peaks still though one at C-OH and the other at C-H3 ? and both won't split because the adjacent thing connected to C is 0 and to H is oxygen, not carbon ?

[Toshiya]

(Original post by master_blaster66)
how does the markscheme explain it?

The revision guide gives the points as;

-Sample injected (1)
-Into inert carrier gas stream (1)
-column/stationary phase consists of high boiling liquid on porous support (1)
-detection of emerging compounds (1)
-compounds distinguished by retention times (1)

with a QWC mark for either stationary, porous or retention spelt correctly.

As I said it's never been in one of the new spec papers so no idea what the mark scheme would say!

[Waki]

Jan 2012 paper, question 1 c iv
What on earth are you ment to right?
I dont get why the mark scheme shows a drawing when itsn ot mentioned anything about drawing in the question?

[mimsicle]

(Original post by navarre)
Addition of acid adds H+ ions, so H+ conc. increases. To counteract this, the equilibrium moves to the left as the yield of HA increases to counteract the increased H+ conc. As the H+ conc. increases, more H+ combines with A- to form HA.

(Original post by cli121)
you have to think of the acid as the H+ ions. Therefore, if more are added position of equilibrium will move to the left to counteract the change.

(Original post by bertiejess)
The H+ in the acid reacts with the A-, forming HA and shifting the pos of equilibrium to the left

Okay I see, have to think of it in terms of H+ ions. Thanks for clearing up the confusion guys

[sydney07]

Hey, I'm getting confused with:

1) functional groups that modify the chromophore
2) functional groups that affect the solubility of the dye
3) functional groups that allow the dye to bond to fibres

I can only think of one for both 1 and 2, but none for 3 :/

[Princess Kawaii]

(Original post by Waki)
Jan 2012 paper, question 1 c iv
What on earth are you ment to right?
I dont get why the mark scheme shows a drawing when itsn ot mentioned anything about drawing in the question?

It does say "Include a full structural formula in your answer" = drawing

You basically have to spot that you need two of those molecules to occupy 32dm3 volume. Sooo
you draw two of them joined via hydrogen bonding

[Bi0logical]

In order for something to be soluble is it basically always this rule;
intermolecular bonds formed are stronger than / similar to those that are borken

[bertiejess]

Also does CO2 have pd-pd bonds or id-id as one mark scheme said pd-pd and the other id-id?

[Bi0logical]

(Original post by sydney07)
Hey, I'm getting confused with:

1) functional groups that modify the chromophore
2) functional groups that affect the solubility of the dye
3) functional groups that allow the dye to bond to fibres

I can only think of one for both 1 and 2, but none for 3 :/

SO3-Na+
This improves the solubility of the dye in water, also due to the ionic group it can form ionic bonds with a protein fibre (e.g. wool)

[Iepnauy]

Can someone explain the assumptions made when a buffer solution?

And assumptions when calculating with weak acids?

[Bi0logical]

(Original post by bertiejess)
Also does CO2 have pd-pd bonds or id-id as one mark scheme said pd-pd and the other id-id?

I think id-id because it's a symmetrical molecule and the charges would balance out so there cant be a pd-pd?

[Hazel247]

(Original post by Cleoleo)
Are Friedel crafts reactions basically any reaction involving the AlCl3 catalyst?
Anyone able to define it please?

Friedel Crafts reactions are an acylation or aklyation of a benzene ring. So basically the adding of an akly group (e.g. CH3) or an acyl group (e.g. RC=O).


The reagent of an aklyation reaction would be CH3Cl, and the AlCl3 is required to create an electrophile out of this compound. It does this by forming an intermediate: AlCl4-, leaving CH3+. This electrophile seeks areas of electron density, for example the benzene ring. It attacks the benzene ring, leaving the overall charge of the compound as positive. A hydrogen on the ring then donates its electron, and forms H+. This H+ then acts as an electrophile by attacking the extra Cl- on the AlCl4-, forming HCl. The AlCl3 is unchanged (which is essential as its a catalyst) and the products are HCl and methylbenzene.

This principle is the same for an acylation reaction, except that RCOCl is used, instead of CH3Cl.

[Princess Kawaii]

(Original post by Iepnauy)
Can someone explain the assumptions made when a buffer solution?

And assumptions when calculating with weak acids?

Are there assumptions for buffer solutions anyway?

Weak Acids:
1. [H+]=[A-] all the [H] come from the acid

2. Initial [HA]= eqiliubrium[HA] weak acids dissociate very little so we can assume the conc of HA is the same at equilibrium as if the acid hadn't dissciated at all.

[Bi0logical]

(Original post by Iepnauy)
Can someone explain the assumptions made when a buffer solution?

And assumptions when calculating with weak acids?

firstly in acids we can assume that the concentration of acid at equilibrium is equal to the concentration of acid initially.
Another assumption is that for every mole of H+ , there is of A-

in buffers:
- all the A- have come from the salt (contribution from the acid is negligible)
- the concentration of the acid in HA is the same as the amount of acid put into the solution.

[sydney07]

(Original post by Bi0logical)
SO3-Na+
This improves the solubility of the dye in water, also due to the ionic group it can form ionic bonds with a protein fibre (e.g. wool)

Thank youuuu!

Anyone know about which functional groups change the chromophore??