AQA CHEM4 - 13th June 2012

do we have to know the indicators and colour changes or will they be given/??/

Think I will go through all of the Jan'10 - Jan'12 papers tomorrow, just to make sure I am updated with the key MS words.

What's everyone's plan for tomorrow?

conditions & definitions

There aren't that many definitions? Most are just common stuff I guess - only a few that you have to really go out of your way and learn lol

Conditions are a bit annoying, thank god there are not too many of them! Need to go through my structure determination chart tomorrow its got arrows and everything

jealous.

yea, the mathy stuff is pretty straight forward, particularly after having phys4 today so its just the knowledge kind of marks i need to make sure i get.

im pretty sure i know all the mechanisms, but ill go over them too.

Does anyone have a list of mechanisms when reflux is required? I know that it is for primary alcohol $\rightarrow$ carboxylic acid, but what are the others that we need to know?

Does anyone have a list of mechanisms when reflux is required? I know that it is for primary alcohol $\rightarrow$ carboxylic acid, but what are the others that we need to know?

reflux...only the aldehyde to carboxylic comes to mind really :s

haloalkane to alkene is naoh/ ethanol with reflux

Thanks. I've searched all of the mark schemes since 2002 and the only other time when reflux was needed in an answer was esterification, where either "heat" or "reflux" was accepted.

I've looked at my AS textbook for haloalkane reactions and reflux wasn't mentioned. Is it needed for both nucleophilic substitution and elimination with NaOH, or just elimination?

Does anyone have a list of mechanisms when reflux is required? I know that it is for primary alcohol $\rightarrow$ carboxylic acid, but what are the others that we need to know?

I dont understand qu 2di and ii on the jan 2011 pper cn sum1 help?

In those questions you have the value for ka and in di. you can work out the moles of HY by doing mole=conc.xvol/1000. You also have the value fore the number of moles of the salt added because it tells you in the question that they are adding 0.0236 moles of the NaY. This means you have the ka, the HY conc and the Y- conc so you rearrange to get the h+ conc and work out the ph.

In the second part you add 0.0005 moles of NaOH. This NaOH will use up some of the acid you originally had so you subtract 0.0005 from the number of moles of acid in the previous question. You are also forming 0.0005 moles more of the salt by adding this NaOH so you add 0.0005 to the 0.0236 moles of Y- that you had before. Once again you have the ka, the conc of HY and the conc of y-, so you just rearrange to get h+ again.

Hope this helps.