Edexcel Chemistry unit 4 discussion- 26/01/11

I take it I'm not the only one looking forward to getting this exam out of the way then? :redface:

Reply 44

emilylikeeee

Original post by Artie

Someone should sue that man!!

"Oh, Im sorry guys, thats my fault. I didnt realise that Id only skimmed that part!"

"That part" being the whole friggin' course!

Reply 45

emilylikeeee

Original post by Kidms001

I take it I'm not the only one looking forward to getting this exam out of the way then? :redface:

Oh no you are not...
Last year with two modules to learn in June I struggled...
But the thought of only having the one to do this summer, its blissful :smile:

Reply 46

tehsponge

Original post by emilylikeeee

Bloody hell, been trying to learn it, its a bitch!
5 proper confusing steps!
How could he just miss it out? Its huge!!??!?!!

Taken directly from the spec:
I can apply a knowledge of the rate equations for the hydrolysis of halogenoalkanes to deduce the mechanisms for primary and tertiary halogenoalkane hydrolysis and to deduce the mechanism for the reaction between propanone and iodine.

I think maybe it will give us two mechanisms and ask us which one is most likely, based on the rate equations stuff. I'm gonna look at past papers later to find a question on it.

Reply 47

emilylikeeee

Original post by tehsponge

Taken directly from the spec:
I can apply a knowledge of the rate equations for the hydrolysis of halogenoalkanes to deduce the mechanisms for primary and tertiary halogenoalkane hydrolysis and to deduce the mechanism for the reaction between propanone and iodine.

I think maybe it will give us two mechanisms and ask us which one is most likely, based on the rate equations stuff. I'm gonna look at past papers later to find a question on it.

Ooo thank you :smile:

That takes the pressure off, as it means we don't have to fully memorise it!

Reply 48

To keep ourselves entertained, how about we move onto the addition of hydrogen cyanide? :tongue:

Then the hydrolysis of nitriles with different acids? :colone:

Reply 49

tehsponge

Original post by Kidms001

To keep ourselves entertained, how about we move onto the addition of hydrogen cyanide? :tongue:

Then the hydrolysis of nitriles with different acids? :colone:

Mechanism is easy enough. What's the reason you use KCN alongside with HCN?

Reply 50

Original post by tehsponge

Mechanism is easy enough. What's the reason you use KCN alongside with HCN?

How about a competition for the best Microsoft Paint mechanism then?

Also, I think the KCN provides the CN

.^-

nucleophiles to initiate the reaction and keep them in supply. My teacher said something about it not being as dangerous as HCN as well :tongue:

Reply 51

mitch.goez

grrr im duin this paper too :frown:

does anyone know where to get the short notes cos ive got 387 pages of detailed notes n its just killin me to keep reading through :frown:

Reply 52

chemdweeb1234

Original post by Kidms001

How about a competition for the best Microsoft Paint mechanism then?

Also, I think the KCN provides the CN

.^-

nucleophiles to initiate the reaction and keep them in supply. My teacher said something about it not being as dangerous as HCN as well :tongue:

Yeah

you are right

the important thing is that HCN is a weak acid...so it is only partially dissociated into ions and thus the concentration of CN- is low and thus the rate of reaction would be slow... the KCN is dissolved with the CN- to increase the [CN-] and this increases the rate of reaction

The mixture is also buffered between a pH of 4 - 5 (need to check on values) and thus is to provide the H+ ions needed for the final step as well :P

Reply 53

Original post by chemdweeb1234

Yeah

you are right

the important thing is that HCN is a weak acid...so it is only partially dissociated into ions and thus the concentration of CN- is low and thus the rate of reaction would be slow... the KCN is dissolved with the CN- to increase the [CN-] and this increases the rate of reaction

The mixture is also buffered between a pH of 4 - 5 (need to check on values) and thus is to provide the H+ ions needed for the final step as well :P

Plus rep for teaching me something that I totally missed in lessons and revision :tongue:

Spoiler

Reply 54

chemdweeb1234

Next topic then...

Esters....How Science Works :P
Where do transfats usually arise from in hydrogenation and why are they bad and how can we overcome them?

Reply 55

RD93

5

Original post by chemdweeb1234

Next topic then...

Esters....How Science Works :P
Where do transfats usually arise from in hydrogenation and why are they bad and how can we overcome them?

Iirc the hydrogenation mechanism has the potential to open up double bonds and convert cis-isomers to trans-isomers, by alternating which sides the hydrogen atoms are bonded to. I don't think you need to know in depth about how they pose health risks, just know that they do. You overcome it by trans-esterification to swap any kinked fatty acid side chains with straighter ones.

Ester + Alcohol switches the alcohol part of the ester with the alcohol you are reacting it with. Someone clarify that for me?

Reply 56

Mally-xo

OP