The big giant AQA CHEM5 thread!!! (May/June 2013) Watch

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laurawoods
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Hello there, thanks for all your help! How to revise chemistry? Have u started looking at past papers yet? I had a look in Xtreme papers for old spec questions but the papers for chem5 appear a bit odd (containing too much of chem4 material )? what would you do to revise at this stage ?
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laurawoods
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#102
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Hello in one of the past exam papers (old syllabus) , I saw this question :

Write an equation for this reaction:
CoCl2 and
CuCl2 using concentrated hydrochloric acid.

But I think this question is out of date? because I couldnt find anything like it in the CGP revsion guide?
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laurawoods
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(Original post by SDavis123)
Boom boom boom!! Know all the colours off by heart now


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Hello in one of the past exam papers (old syllabus) , I saw this question :

Write an equation for this reaction:
CoCl2 and
CuCl2 using concentrated hydrochloric acid.

But I think this question is out of date? because I couldnt find anything like it in the CGP revsion guide?
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Beth_L_G
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#104
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#104
(Original post by laurawoods)
Hello there, thanks
Have you started doing the past papers yet. I had a look at Xtreme papers to get hold of the past syllabus questions but the questions in the papers seem a bit odd. How are u revising Chemistry at the moment?
I'm starting past papers from the start of April. I finished my notes in my last chem session so now I'm just reading through them and learning them by heart, by reading them and listening to them through the vids I put on youtube
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laurawoods
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(Original post by Beth_L_G)
I'm starting past papers from the start of April. I finished my notes in my last chem session so now I'm just reading through them and learning them by heart, by reading them and listening to them through the vids I put on youtube
Hello, pls can u send me a link to the videos that you uploaded! thank you, might help me as well.

Also , if u dont mind me asking, what did u get in chem4 exam?

Also, did you come across CoCl2 etc,,, they seem to be in the past papers ((old syllabus)) . I get ocnfused when i come across these in the past papers. thanks!
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Beth_L_G
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(Original post by laurawoods)
Hello, pls can u send me a link to the videos that you uploaded! thank you, might help me as well.

Also , if u dont mind me asking, what did u get in chem4 exam?

Also, did you come across CoCl2 etc,,, they seem to be in the past papers ((old syllabus)) . I get ocnfused when i come across these in the past papers. thanks!
They're all here http://www.youtube.com/feed/UC9F-vfa-lqPgYUzE2mQoAWg/u

Got a b in chem 4.

CoCl2 may come up, it is on the syllabus
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laurawoods
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(Original post by Beth_L_G)
They're all here http://www.youtube.com/feed/UC9F-vfa-lqPgYUzE2mQoAWg/u

Got a b in chem 4.

CoCl2 may come up, it is on the syllabus
It is on the syllabus? I couldn't see any colour changes etc associated with them? Pls could you provide a bit of info on them if you dont mind...what do we need to know about them...in one of the past questions we had to write an equation for reaction of CoCl2 with HCl conc.
what do we write for this?

well done on the B. Nice one! congrats!
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TLi1295
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#108
(Original post by laurawoods)
Hello , I dont really seem to be understanding this concept of Al and Cr being amphoteric? I do know the definiton of what amphoteric is but I dont really know what is happening in terms of the chemistry? help!! How come the Al and Cr can act as both acids and bases? pls can you explain a) a reaction where they are acting as acids and then b) a reaction when they show basic properties ?

pls pls pls
It is the hydroxides of Al and Cr that are amphoteric. So the white precipitate [Al(OH)3(H2O)3] will react with OH- to produce [Al(OH4)(H2O)2], a colourless solution. But it will also react with H+ to go back to the hexaaqua ion [Al(H2O)6]3+ which is also a colourless solution.

The grey-green precipitate [Cr(H2O)3(OH)3] is amphoteric as it reacts with OH- to produce [Cr(OH)6]3- (a dark green solution) and it reacts with H+ to produce [Cr(H2O)6]3+ which should be a ruby-coloured solution.
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erniiee
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(Original post by laurawoods)
I am confused about this concept of ammonia being able to act as a base as well as a ligand.

In the revision guide, there are two different equations, one for the formation of a ppt and one when the NH3 is being used in excess (a ligand substitution reaction is occurring). But i don't really understand which one out of these two is the equation which is appropriate to show ammonia acting as a Lewis base and why?

It is specified, in the CGP guide, that the base is Bronsted Lowry base and that when it is acting as a ligand , it is a lewis base. Aren't there any similarities between these bases because I thought all Lewis bases are Brosted Lowry bases too!
A Lewis base is an electron pair donor. Ammonia donates an pair of electrons to form a coordinate covalent bond to the metal ion when it is in excess (only with Chromium, Copper and Cobalt iirc). Therefore, when ammonia is in excess and undergoes some kind of ligand exchange with water, it is being a Lewis base.

I don't know if all are, but a Bronsted-Lowry base is a proton acceptor; if you can accept protons, you most likely can donate a lone pair to behave as a Lewis base.
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SDavis123
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#110
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(Original post by laurawoods)
Hello in one of the past exam papers (old syllabus) , I saw this question :

Write an equation for this reaction:
CoCl2 and
CuCl2 using concentrated hydrochloric acid.

But I think this question is out of date? because I couldnt find anything like it in the CGP revsion guide?
ermm do you mean CoCl2 and CuCl2 reacting separately with conc HCl?
or combined i.e CoCl2 +CuCl2 + HCl -> .....?

if its combined I have no clue whatsoever

if separately if memory proves right,
CoCl2 + 2HCl -> [CoCl4]2- (blue) + 2H+

CuCl2 + 2HCl -> [CuCl4]2- (yellow) + 2H+

I'm not 100% sure on the equation but I'm pretty certain the complexes (in bold) are correct.
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laurawoods
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(Original post by TLi1295)
It is the hydroxides of Al and Cr that are amphoteric. So the white precipitate [Al(OH)3(H2O)3] will react with OH- to produce [Al(OH4)(H2O)2], a colourless solution. But it will also react with H+ to go back to the hexaaqua ion [Al(H2O)6]3+ which is also a colourless solution.

The grey-green precipitate [Cr(H2O)3(OH)3] is amphoteric as it reacts with OH- to produce [Cr(OH)6]3- (a dark green solution) and it reacts with H+ to produce [Cr(H2O)6]3+ which should be a ruby-coloured solution.
Hello, yes thanks but what are the two quations for showing the amphoteric properties of aluminium hydroxide?
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laurawoods
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#112
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(Original post by erniiee)
A Lewis base is an electron pair donor. Ammonia donates an pair of electrons to form a coordinate covalent bond to the metal ion when it is in excess (only with Chromium, Copper and Cobalt iirc). Therefore, when ammonia is in excess and undergoes some kind of ligand exchange with water, it is being a Lewis base.

I don't know if all are, but a Bronsted-Lowry base is a proton acceptor; if you can accept protons, you most likely can donate a lone pair to behave as a Lewis base.
Hello there! thanks.

Just some more questions I need ur help with. I hope u can help me?

1) What is the equation for the oxidation of Co2+ containing species to a Co3+ containing species and what is the reagent required?
2) What are the two equations we write to show the amphoteric properties of aluminium hydroxide?
3) What is the equation for the reaction of CoCl2 with HCl?
4) What is the test and observations for distinguishing between CrCl3 and FeCl2?

I think that is it for now. thanks! any revision tips for chem5?
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erniiee
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(Original post by laurawoods)
Hello there! thanks.

Just some more questions I need ur help with. I hope u can help me?

1) What is the equation for the oxidation of Co2+ containing species to a Co3+ containing species and what is the reagent required?
2) What are the two equations we write to show the amphoteric properties of aluminium hydroxide?
3) What is the equation for the reaction of CoCl2 with HCl?
4) What is the test and observations for distinguishing between CrCl3 and FeCl2?

I think that is it for now. thanks! any revision tips for chem5?
1) I think that's ammoniacal cobalt(II) being oxidised by air (I'm guessing oxygen within it) to ammoniacal cobalt (III).

2) I don't know these equations off the top of my head sorry - have a look in your textbook maybe? One will be Al(OH)3(H2O)3 reacting with an OH- ion to form an Al(OH)4 containing complex. The other would be reaction with H+ ions/HCl.

3) [Co(H2O)6]2+ + 4Cl- -> [CoCl4]2- + 6H2O

4) No clue - maybe add excess ammonia? Purple solution formed with the CrCl3 (which exists as [Cr(H2O)6]2+), green gelatinous precipitate formed with iron(II) ions?
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Dalts
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(Original post by laurawoods)
Hello there! thanks.

Just some more questions I need ur help with. I hope u can help me?

1) What is the equation for the oxidation of Co2+ containing species to a Co3+ containing species and what is the reagent required?
2) What are the two equations we write to show the amphoteric properties of aluminium hydroxide?
3) What is the equation for the reaction of CoCl2 with HCl?
4) What is the test and observations for distinguishing between CrCl3 and FeCl2?

I think that is it for now. thanks! any revision tips for chem5?
1) you could use oxygen to do this oxidation, however it is very slow and they ask for a reagent, therefore H2O2 (hydrogen peroxide) will do it, make sure you use the half-equations and make it under alkaline conditions.

2) Under alkaline you would produce [Al(OH)4(H2O)2]-1 and acidic you add a strong acid and produce the original [Al(H2O)6]+3 solution which due to the +3 charge on the Al is acidic therefore amphoteric

3) CoCl2 will be equivalent to [Co(H2O)6]+2 and therefore is simply that with 4Cl- producing [Co(Cl4)]-2 and it is blue.

4) We know Cr is more acidic than Fe due to the different charges (+3 and +2 respectively) therefore add CO3 -2 to both and due to Cr+3 being acidic enough it will liberate the CO2 resulting in effervescents, and no change in Fe.
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loknath
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How are people revising for chem this Easter?
Are people revising????
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popnit
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#116
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(Original post by loknath)
How are people revising for chem this Easter?
Are people revising????
These techniques http://www.thestudentroom.co.uk/show....php?t=2185709

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Beth_L_G
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(Original post by loknath)
How are people revising for chem this Easter?
Are people revising????
Notes and past papers during the day

Listening to my notes in the evening when my eyes have gone to sleep http://www.youtube.com/feed/UC9F-vfa-lqPgYUzE2mQoAWg/u
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laurawoods
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(Original post by Beth_L_G)
Notes and past papers during the day

Listening to my notes in the evening when my eyes have gone to sleep http://www.youtube.com/feed/UC9F-vfa-lqPgYUzE2mQoAWg/u
Hello , do u know how many papers there are to do , including all the legacy papers?
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laurawoods
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(Original post by Beth_L_G)
Notes and past papers during the day

Listening to my notes in the evening when my eyes have gone to sleep http://www.youtube.com/feed/UC9F-vfa-lqPgYUzE2mQoAWg/u
Hello, I tried doing some of the legacy past papers ?> have u tried doing them yet?
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laurawoods
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The addition of sodium hydroxide or of sodium carbonate to aqueous chromium(III)
chloride results in the formation of the same green precipitate.
2[Cr(H2O)6]^3+ +3CO32- --> 2[Cr (H2O)3(OH)3 ] +3CO2 +3H2O

State the role shown by sodium carbonate in the formation of this precipitate Cr (H2O)3(OH)3.
And please can someone explain why it is not a ligand?

thanks in advance !
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