Edexcel - Chemistry Unit 2 - 4 June 2013

OP

Original post by Gnome :)

Ah no

What do you need to get? I'm hoping I'll get it, but the evil AQA examiners decided to make U5 biology esssay based, and I cannot do timed essays AT ALL.

I need 124 UMS total for 2 and 5 for a B, or 184 for an A. Don't think I'll get the A though :/

Ah yh, I dropped biology the first month of AS! God knows how much worse my case would have been had I not :frown:

I need about the same :smile:

if not more... because I've assumed I'll get 80/120 UMS for my practical assessments!

Which unit do you feel overlaps the most with unit 5 ?

Reply 42

Gnome :)

Original post by posthumus

Ah yh, I dropped biology the first month of AS! God knows how much worse my case would have been had I not :frown:

I need about the same :smile:

if not more... because I've assumed I'll get 80/120 UMS for my practical assessments!

Which unit do you feel overlaps the most with unit 5 ?

Have to say that I really enjoy bio, and find it relatively easy in terms of content... It's just the essay!

Guess we just have to push through it and get on with revising then :smile:

I think units 2 and 5 fit together quite nicely with the organics and all that jazz, but everything's meging into one now :tongue:

Reply 43

OP

Original post by Gnome :)

Have to say that I really enjoy bio, and find it relatively easy in terms of content... It's just the essay!

Guess we just have to push through it and get on with revising then :smile:

I think units 2 and 5 fit together quite nicely with the organics and all that jazz, but everything's meging into one now :tongue:

I guess bio was just never for me :biggrin:

I find some aspects interesting but thought there was too much content :frown:

And I really hate questions where you have to write more than 2 lines!

Ah yh, I am finding it so much more difficult and tedious this time round to study! I keep thinking I will forget all this anyway, so what is the point :frown:

I have to say these forums are really really useful! :redface:

I'm going to get some sleep now, so speak to ya soon ! :smile:

Reply 44

OP

Original post by geor

Could someone take me through the steps of purifying a halogenoalkane after the intial distillation?
Always get a bit confused!

What I don't get is why the grade boundaries are higher for this exam than unit 1, when unit 2 is so much harder? :confused:

Okay so you firstly add the halogenoalkane into a separating funnel with water.... you will get 2 layer - the aqueous layer on top of the halogenoalkane would have most of the impurities - so get rid of that layer :smile:

There may still be some acid impurities in the solution so we add a very strong base - sodium carbonate (Na2CO3) or sodium hydrogen carbonate (NaHCO3), here's the formula if your interested :smile:

:

Na2CO3 + 2H+ ------> Na+ + H2O + CO2
or
NaHCO3 + H+ -------> Na+ + H2O + CO2

Transfer the halogenoalkane again into a seperating funnel with water and remove the top layer again.... your halogenoalkane should be even more pure now ! :smile:

Now in dry test tube add a drying agent (such as anhydrous calcium chloride) this will remove any water... once complete you should have some very dry halogenoalkane....

.... transfer this into a fractional distillation apparatus and distill :smile:

I'd take a guess and say that there are more entries for unit 1 & that quite a few people may drop the subject after that, but who knows :tongue:

Also because it's January there are many A2 students who sit the exams (like myself :colondollar:

).

Reply 45

phaseshift

12

Original post by geor

Could someone take me through the steps of purifying a halogenoalkane after the intial distillation?
Always get a bit confused!

What I don't get is why the grade boundaries are higher for this exam than unit 1, when unit 2 is so much harder? :confused:

The AS Unit 2 isn't that bad, but there is a lot to remember. Although it would be nice if the grade boundaries were a little nicer.

Reply 46

Does anyone have an easy way of remembering which functional groups get absorbed at a specific wavelength in a IR spectrum? :frown:

Reply 47

OP

Original post by MSamuel

Does anyone have an easy way of remembering which functional groups get absorbed at a specific wavelength in a IR spectrum? :frown:

You don't need to remember that do you ?

All that information is in the data booklet provided :smile:

Reply 48

Original post by posthumus

You don't need to remember that do you ?

All that information is in the data booklet provided :smile:

Oh good, I got worried there. Thank you!
Any idea of what I can expect in the unit 2 exam?

Reply 49

And also does can anyone explain SN1 and SN2 mechanisms to me.. CGP doesn't even mention it and im totally lost.

Reply 50

phaseshift

12

Original post by MSamuel

And also does can anyone explain SN1 and SN2 mechanisms to me.. CGP doesn't even mention it and im totally lost.

The S_n1 mechanism will give rise to a carbocation; there is effectively two/three steps:

1.

The original substrate, splits into the carbocation and the leaving group.

2.

The carbocation is then attacked by an arriving ground (nucleophile) which results in a new substrate.

Whereas the S_n2 mechanism is effectively a one-step mechanism with a transition state (both leaving and arriving groups are 'attached'at once - http://upload.wikimedia.org/wikipedia/commons/f/f9/BromoethaneSN2reaction-small.png

Reply 51

Original post by HarryMWilliams

The S_n1 mechanism will give rise to a carbocation; there is effectively two/three steps:

1.

The original substrate, splits into the carbocation and the leaving group.

2.

The carbocation is then attacked by an arriving ground (nucleophile) which results in a new substrate.

Whereas the S_n2 mechanism is effectively a one-step mechanism with a transition state (both leaving and arriving groups are 'attached'at once - http://upload.wikimedia.org/wikipedia/commons/f/f9/BromoethaneSN2reaction-small.png

In the exam, is it likely that we'll get a question asking us to draw one of the 2 mechanisms do you think?

Reply 52

phaseshift

12

Original post by MSamuel

In the exam, is it likely that we'll get a question asking us to draw one of the 2 mechanisms do you think?

If I remember correctly, some questions will ask you to compare the two separate mechanisms or identify the key features of each mechanism.

Reply 53

OP