Ed excel Chemistry A2 12th June, Wednesday

Who's using the George Facer book to prepare for this unit ?

In January I memorized and learnt every bit of information in that book... now I'm starting to think I had wasted my time

Should I just go through a revision guide or start past papers right away

umm with me I like reading some more than just what the spec needs so I always thought using george facer was the best way to prepare for exam.
Umm go through the spec and if u are not sure then go through text book first coz revision guides have very condensed information unlike the book which actually helps u to understand the topic

Thanks The issue with me is, I'm too obsessed with reading the George Facer book over and over again, like 100 times

I think I'll make doing past papers a much larger priority this time !

Hopefully this thread will get a lot more busy as well over the next few days, maybe if we get a Mod to add "Unit 4" into the thread title... more people will join

How's revision going for you anyway ?

- Are there any special conditions for the iodoform reaction? Like heating/refluxing?
- For making a carboxylic acids from the iodoform reaction, do we have to heat the mixture after adding excess strong acid (H+)
or will the carboxylic acid form straight away?

- Gentle warming

- No I think you would have to add excess dilute strong acid afterwards, such as HCl... that's if you'd like to have the carboxylic acid and not the salt

[June 2010]
Q14) Which of the following solutions, when mixed, would make a buffer with pH
more than 7?
A Methanoic acid and sodium methanoate.
B Sodium hydroxide and sodium chloride.
C Ammonia and ammonium chloride.
D Ammonium chloride and ammonium ethanoate.

Could someone explain this please? I still don't get the theory behind it.

- [June 2010]
Q5) Which of the following reacts with hydrogen cyanide, HCN, to make a racemic mixture?
A Methanal, HCHO
B Ethanal, CH3CHO
C Propanone, CH3COCH3
D Pentan-3-one, C2H5COC2H5

The answer is B, but how are A and C wrong? Both are planar right? So CN- can attack from top or bottom..

- To distinguish propanone from propan-1-ol, would warming each compound with Fehling’s or Benedict’s solution work ?

- How does adding water, drop by drop to each, distinguish ethanoyl chloride from ethanol?

Thanks

Is it C? I think ammonia is the strongest base and ammonium chloride is pretty weak




Propanone + HCN is a standard reaction which you should know for this paper. The CN can attack from either top or bottom to form a racemic solution as there is a chiral center. A does not have a chiral center.. the end result will have a carbon with 1 CN group, 1 OH group & 2 Hydrogens ! For it to be a chiral center, all four attached groups must be different. Same goes for C... the end result will have a carbon center which has 1 CN group, 1 OH group but 2 CH3 groups.

-No Tollen's reagent also reduces Fehling's and Benedict's solutions.

- Possibly yes, I need to get cracking with this unit lol forgotten so much But ethanoyl is extremely reactive with water, so I guess you could just distinguish it from that

Unit 4, my old friend.

How is everyone coping?

I find chemistry hard and have to take an exam on c1,2,3 a module test with three chapters. What would u suggest would be the main points to revise? Help please


Posted from TSR Mobile

x

Hey guys would anyone know the answer to this: is confusing me so much. Please help.

Question: A mother was overheard talking to a child" you were made in heaven using stardust" give 2 scientific evidence to back up this claim.


Posted from TSR Mobile

guys there's a thread just for unit 4 : http://www.thestudentroom.co.uk/showthread.php?t=2372695