AQA CHEM2 ~ May 23rd 2012 ~ AS Chemistry

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Awwwh you guys! :')

People keep saying Unit 2 is difficult. But trust me, you will all be fine, and you will all do great!
It looks like you all hit revision mode a long time ago, so some of you will feel confident, and others maybe not so much, but it isnt too bad!

Make sure your mechanism knowledge is solid proof- max marks there. And those of you considering staying on to year 13, then make mechanisms your best friend! Trust me, unit 4 is ALL organic. Mech after mech! Carbon after carbon! :tongue:

Unit 5 is pure physical chemistry. Good for those of you who are solid at maths.

It will get better over the course!

Good luck to all tomorrow. I was in your position this time last year (in yr 13 now!).

awww... that wo sooo sweet. thankuu.

Reply 1581

MathMad

Original post by hus11128386

wat are alkyl groups??

They're alkanes with a hydrogen removed such as CH3-.
But anyway, it's because the alkyl groups 'feed' electron towards the positve charge of the carbocation.

Q: Why is the carbon-halogen bond in haloalkanes polar?

Reply 1582

Jack_Smith

Original post by hus11128386

wat are alkyl groups??

CH3, C2H5 << are example of alkyl groups =D

Reply 1583

Mike Hunt is nice

Original post by MathMad

*Highest.

And to remove any ions which might interfere with the test.

Q: State Le Chateliers principle.
Q: Explain what is meant by the term dynamic equilibrium.
Q: Explain why catalysts don't affect the position of equilibrium.
(7 marks)

Yeh, dude, can i just ask. Do you have a dictionary definition of Dynamic eq?
the books just ramble..

Reply 1584

shuaib786

Original post by hus11128386

wat are alkyl groups??

ch3/c2h5/c3h8 etc.they are mainly used for chain isomers. For your previous post the mark schemes are every from the old spec to even the one of the A level chem site. Im not sure if purple fumes is right though, because in its standard state you can have a black solid. In the book it just states steamy fumes.

Reply 1585

hus11128386

Original post by MathMad

because they have diff electronegativity values???

Reply 1586

Thasneemy

Original post by hus11128386

awww... that wo sooo sweet. thankuu.

No problem!
If anyone needs any help with any theory, i'll try my best to bring out the dusty unit 2 from my past!

Reply 1587

06bhandal

can any1 help me how to understand how to work out the charges on inoic queations ? like how do u know when its 3+ ..
also, when a question says copper (IV) oxide, what does the IV mean, pleaseee need help!!!!!!!!!!!!!!!!!!!!!!

Reply 1588

CollateralElement

Original post by hus11128386

alkyl groups ???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????

Alkyl groups are the methyl/ethyl groups etc. Methyl = CH₃
Ethyl = CH₃CH₂

Is there something specific that you're freaking out about? :smile:

Reply 1589

nicecookie

Had so many exams lately and I hardly did any revision for chem unit 2 until today :/
Only just finished past papers...
Need to start revising the things...
I'm so screwed...

Feel sorry for those who have two exams tomorrow

Reply 1590

MathMad

Original post by Mike Hunt is nice

Yeh, dude, can i just ask. Do you have a dictionary definition of Dynamic eq?
the books just ramble..

A dynamic equilibirum is when forwards and backwards reactions in a closed system continue but at the same rate, and also the concentraition of products and reactants remain constant :smile:

You need to understand that dynamic equilibirum can only happen in a closed system (one in which no products and reactants can't escape)

Reply 1591

Jack_Smith

why are compromise conditions used?

Reply 1592

Seatbelt

Best of luck to those doing this exam :smile:

Reply 1593

Madara

Original post by MathMad

Q: Explain why Bromine is a better reducing agent than Fluorine :smile:

Reducing agents are oxidised and therefore lose electrons.
Bromine is a better reducing agent because it is a larger atom due to having more main energy levels therefore its outer electrons are further away from the nucleus and feel less of the nuclear charge due to the increased electron shielding. Fluorine is a smaller atom with less sheilding due to less main energy levels. Its electrons are therefore attracted closer to the nucleus and are harder to remove.

Reply 1594

CollateralElement

Original post by Mike Hunt is nice

Yeh, dude, can i just ask. Do you have a dictionary definition of Dynamic eq?
the books just ramble..

Dynamic Equilibrium : The forward rate of reaction is equal to the backward rate of reaction
The concentrations of the reactants and products remain constant

I doubt they'll ask you anything further than that :smile:

Reply 1595

gills10

Original post by MathMad

Q: Why is the carbon-halogen bond in haloalkanes polar?

Because the halogen is more electronegative than the carbon so the electron in the bonds are attracted more to the halogen which are dipole-dipole forces

Reply 1596

shuaib786

Original post by Jack_Smith

why are compromise conditions used?

For a balance between the rate of reaction and yield of product.

Reply 1597

shuaib786

Original post by Thasneemy

No problem!
If anyone needs any help with any theory, i'll try my best to bring out the dusty unit 2 from my past!

If you mind me asking what ums did you get???

Reply 1598

MathMad

Original post by hus11128386

because they have diff electronegativity values???

Yep

Halogens are more electronegative than carbon.

Q: a) Explain what catalyst you would use to react with an alkene to make alcohols.
b) Once the acid is added to the alkene, a reaction takes place. Name this reaction.
c) Explain how you could then make an alcohol from the product which has undergone the reaction with alkene.
d) What is the role of the acid in the whole of this reaction?

That's everything covered on how alkenes can be made into alcohols really, you just need to learn how to draw the mechanism :smile:

Reply 1599

Madara

Original post by Jack_Smith

why are compromise conditions used?

To make it proffitable and also energy efficient. A high temperature increases the rate of reaction but also increases energy costs whereas a low temperature costs less to run but the reaction occurs too slow and isnt economically viable. So compromise conditions are used so the reaction occurs fast enough but doesnt require such high temperature/pressure which would cost a lot of money.