[L.Shep]

does anyone have a link/online copy of this paper and mark scheme please?

any help would be much appreciated

[clownfish]

(Original post by L.Shep)
does anyone have a link/online copy of this paper and mark scheme please?

any help would be much appreciated

Here you go.

[excell]

(Original post by clownfish)
Here you go.

Just wondering if you have the same for CHEM4?

Thanks.

[clownfish]

(Original post by excell)
Just wondering if you have the same for CHEM4?

Thanks.

Sure

[excell]

Cheers mate!

[xpolly123x]

(Original post by clownfish)
Here you go.

do you have bio unit 5 aqa jan 2012 paper/mark scheme? desp, help please!

[clownfish]

(Original post by xpolly123x)
do you have bio unit 5 aqa jan 2012 paper/mark scheme? desp, help please!

Sorry I don't do biology.

[rainbow1994]

does any one have the physics unit 5 aqa jan 2012 paper?

[Brightbud]

Do you have one for unit 2 chem jan 2012?? thanks

[clownfish]

(Original post by Brightbud)
Do you have one for unit 2 chem jan 2012?? thanks

Here you go.

[Amy-Rose]

(Original post by clownfish)
Here you go.

Going to ask you to complete the set hehe, any chance of unit 1?

[clownfish]

(Original post by Amy-Rose)
Going to ask you to complete the set hehe, any chance of unit 1?

Here you go!

(I'm thinking I should have done Clownfish's super thread of papers )

[Amy-Rose]

(Original post by clownfish)
Here you go!

(I'm thinking I should have done Clownfish's super thread of papers )

You so should, you're a star! Thanks.

[*QueenBeee]

Hey guys! I'm after some chemistry help for my exam and will be so grateful if anyone could offer me a helping hand!!!

A) {Cr(OH)6}"-3 charge"...add hydrogen peroxide (bubbles of gas and heat produced)...................CrO4 "2-"
State & explain the following
Work out the oxidation state Of chromium in each compound.??
What happened to chromium in terms of Redox in this reaction??


B) Identifying organic solids
What would you use the following to identify?
1cm of sulphuric acid
1 cm potassium dichromate solution
*
*
*
C) Identifying organic solids
Acidified potassium dichromate changes from orange to blue green
*The dichromate ions become chromium (III) ions. Is this oxidation or reduction?
*What happens to the organic compounds in this test?
Which organic compounds containing oxygen do not react with acidified potassium dichromate? Why do they not react?
*
*
D) Identifying organic solids
Draw the skeletal formula of three possible isomers of an alcohol containing 6 carbon atoms.
This alcohol cannot be oxidised by acidified potassium dichromate

[clownfish]

(Original post by *QueenBeee)
Hey guys!

A) {Cr(OH)6}"-3 charge"...add hydrogen peroxide (bubbles of gas and heat produced)...................CrO4 "2-"
State & explain the following
Work out the oxidation state Of chromium in each compound.??
What happened to chromium in terms of Redox in this reaction??

When we find the oxidation state of elements in a compound containing oxygen, if it is not a peroxide (nor is bonded to fluorine), we take oxygen to be -2, and hydrogen is +1 (unless hydrogen is bonded to a grp 1, 2 or 3 metal), so:

Cr(OH)₆^3- has 6 oxygens = 6x-2 = -12 and six hydrogens = 6 x +1, so 6OH- = -12+6 = -6
The overall charge is -3, so the chromium charge must be the difference between the -6 charge and the net -3, so -3-6 = +3 so the oxidation number of Chromium is +3.

I'll leave you to try and do the other one.

B) Identifying organic solids
What would you use the following to identify?
1cm of sulphuric acid
1 cm potassium dichromate solution

acidified dichromate is an oxidising agent, so what do you know in organic chemistry that can be oxidised?

C) Identifying organic solids
Acidified potassium dichromate changes from orange to blue green
*The dichromate ions become chromium (III) ions. Is this oxidation or reduction?
*What happens to the organic compounds in this test?
Which organic compounds containing oxygen do not react with acidified potassium dichromate? Why do they not react?

The formula of dichromate is Cr₂O₇^2-, so work out the oxidation number of chromium in this species and then compare it is chromium (III) ions - has chromium been oxidised (become more positive) or reduced (become more negative)?

As per the earlier question, it is an oxidising agent, so the organic compounds will have been oxidised.

You should know of organic groups that cannot be oxidised. I'll give you one - tertiary alcohol, but there are some others too.

D) Identifying organic solids
Draw the skeletal formula of three possible isomers of an alcohol containing 6 carbon atoms.
This alcohol cannot be oxidised by acidified potassium dichromate

So you need to draw as many isomers as you can, perhaps while you'll getting confident with skeletal you might want to do with normal displayed formulae to help you. To give you a clue, you could have hexan-1-ol, hexan-2-ol etc and also you could have methyl groups coming off smaller chains. Do be careful not to draw the same molecule twice eg hexan-5-ol is the same as hexan-2-ol by symmetry.

Tertiary alcohols cannot be oxidised, so find one of your structures which has the carbon with OH on also attached to three other carbons.

[*QueenBeee]

(Original post by clownfish)

A) {Cr(OH)6}"-3 charge"...add hydrogen peroxide (bubbles of gas and heat produced)...................CrO4 "2-"
State & explain the following
Work out the oxidation state Of chromium in each compound.??
What happened to chromium in terms of Redox in this reaction??

When we find the oxidation state of elements in a compound containing oxygen, if it is not a peroxide (nor is bonded to fluorine), we take oxygen to be -2, and hydrogen is +1 (unless hydrogen is bonded to a grp 1, 2 or 3 metal), so:

Cr(OH)₆^3- has 6 oxygens = 6x-2 = -12 and six hydrogens = 6 x +1, so 6OH- = -12+6 = -6
The overall charge is -3, so the chromium charge must be the difference between the -6 charge and the net -3, so -3-6 = +3 so the oxidation number of Chromium is +3.

I'll leave you to try and do the other one.

B) Identifying organic solids
What would you use the following to identify?
1cm of sulphuric acid
1 cm potassium dichromate solution

acidified dichromate is an oxidising agent, so what do you know in organic chemistry that can be oxidised?

C) Identifying organic solids
Acidified potassium dichromate changes from orange to blue green
*The dichromate ions become chromium (III) ions. Is this oxidation or reduction?
*What happens to the organic compounds in this test?
Which organic compounds containing oxygen do not react with acidified potassium dichromate? Why do they not react?

The formula of dichromate is Cr₂O₇^2-, so work out the oxidation number of chromium in this species and then compare it is chromium (III) ions - has chromium been oxidised (become more positive) or reduced (become more negative)?

As per the earlier question, it is an oxidising agent, so the organic compounds will have been oxidised.

You should know of organic groups that cannot be oxidised. I'll give you one - tertiary alcohol, but there are some others too.

D) Identifying organic solids
Draw the skeletal formula of three possible isomers of an alcohol containing 6 carbon atoms.
This alcohol cannot be oxidised by acidified potassium dichromate

So you need to draw as many isomers as you can, perhaps while you'll getting confident with skeletal you might want to do with normal displayed formulae to help you. To give you a clue, you could have hexan-1-ol, hexan-2-ol etc and also you could have methyl groups coming off smaller chains. Do be careful not to draw the same molecule twice eg hexan-5-ol is the same as hexan-2-ol by symmetry.

Tertiary alcohols cannot be oxidised, so find one of your structures which has the carbon with OH on also attached to three other carbons.

Pal u have no idea how thankful I am. This has helped me loads, thanks for taking the time and sharing all the info! xxx

[sandford]

hi guys
just wondering if any of you can explain question 8e(i) on the unit 5 chem jan 2012?
the links have already been posted further up
thanks

[SY102482]

Does anyone know where I can find the Biology unit 4 jan 2012 paper?

[LogicGoat]

(Original post by clownfish)
Here you go.

Hi, sorry to bother you, but would you happen to have the june 2012 paper and mark scheme for CHEM5?