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Edexcel Chemistry Unit 5 June 19 2012

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um reallly scared with the synoptic questions...specially regarding Organic synthesis routes.....i seem to forget them always.....any advise what i myt do?????

Reply 81

Chaofan88

quick question guys, [Cr(H2O)6]3+ is purple right? Providing there are only water ligands swimming around.

Reply 82

marcus94

Original post by Abrar_Higuain

um reallly scared with the synoptic questions...specially regarding Organic synthesis routes.....i seem to forget them always.....any advise what i myt do?????

Do a massive flow chart for all the reactions you have learnt over the last two years.

Original post by Chaofan88

quick question guys, [Cr(H2O)6]3+ is purple right? Providing there are only water ligands swimming around.

I've remembered it as green but i remember someone saying they thought it was purple/green colour and some said purple. im guessing they will accept all on a mark scheme though. Best thing to do is go check on a ms somewhere - im sure there has been a question on it previously

Reply 83

arnab

Original post by giraffegiraffe

no our teacher said we just need to know the electrophile is SO3 and the product is benezenesulfonic acid, but we don't need the mechanism :biggrin:

Original post by King_Arthur

i don't think need to but it's not that different from any other E+ substitution
http://www.chemguide.co.uk/mechanisms/elsub/sulphonation.html

Thank you both!

Reply 84

arnab

Guys what do we need to know about application of aromatic compounds?

Reply 85

NutterFrutter

Original post by arnab

Guys what do we need to know about application of aromatic compounds?

Can you expand on this. What do you mean by "application"?

Reply 86

NutterFrutter

Original post by Chaofan88

quick question guys, [Cr(H2O)6]3+ is purple right? Providing there are only water ligands swimming around.

It's actually green. Technically it's blue-violet but because of negative ions in the solution (e.g. Cl-) they can replace one of the water ligands and so it appears green.

You'd never only get water ligands but yes if that was the case then it would be a purple (violet) colour. They'd probably accept green/purple/violet/blue-violet/ruby

Reply 87

Backflip

Original post by arnab

Guys i have a big question > you see complex ions with 4co-ordination number, WHY do they form two isomers (tetrahedral and square planner)?

There are no hard and fast rules for whether it will form a tetrahedral or square planar complex. However, square planar complexes form almost exclusively with metal ions with the d^8 configuration.
For example; Cisplatin Pt(NH3)2(Cl-)2 forms a square planer complex which is one to be aware of. Another example is [Ni(CN-)4]2-.

Reply 88

Backflip

Original post by arnab

Guys what do we need to know about application of aromatic compounds?

Vague... but dyes are a major use. Pharmaceuticals is a general point. Sulphonation of aromatic rings is an important reaction in the manufacture of many detergents/surfactants.

Reply 89

Jukeboxing

Original post by XiaoXiao1

Cheers that's really helpful, only isn't Cr 3+ Green?

Like i said, some may not agree with the colours but my teacher did all the reactions in front of the class, so thats where I got the colours from.

Original post by arnab

are you sure this is right?

For Cr with OH-

Blue-purple solution >>>>>>> Muddy green precipitate

[Cr(H2O)6]3+ + 3NH3 >>>>>>>> [Cr(H2O)3(OH)3] + 3NH4+

I thought the formula for the purple solution was [Cr(Nh3)6]3+? :s-smilie:

It is correct, [Cr(NH3)6]3+ is what you get when dissolve the Cr3+ in excess NH3

Reply 90

username889170

Original post by shahofiran

Also, why is Mn(II) more stable than Mn(III)?

Mn(II) has an extra electron, it is more charged dense, hence more stable

Reply 91

nmudz_009

Original post by marcus94

basically if there is only one type of ligand its going to be tetrahedral and if there are two different types of ligands its going to be square planar. thats how ive learnt it

Isn't (Ni(cl)4) ^2- square planer? :s-smilie:

Reply 92

nmudz_009

Original post by giraffegiraffe

I get confused on this too. Our teacher has told us that if the coordination number is 4, assume its Tetrahedral, unless the compound is Pt(NH3)2Cl2 which is the one we have to know as being square planar (and also (NiCl4)2-)

Hey

Are those two the only square planar molecules we need to know about?

Reply 93

nmudz_009

Original post by Chaofan88

quick question guys, [Cr(H2O)6]3+ is purple right? Providing there are only water ligands swimming around.

erm my teacher actually said green violet, but colours are subjective I guess :s-smilie:

Reply 94

giraffegiraffe

Original post by nmudz_009

Hey

Are those two the only square planar molecules we need to know about?

Yess i think the main one to be aware of is the Pt.... one :smile:

Reply 95

EffKayy

Original post by Jukeboxing

Wanna scriblink in like an hour? :P

Reply 96

bsblitter

Can someone explain to me when we have to use the platinum electrode in the half cells?

thanks

Reply 97

11billi11

Can some one please help on transitional metal colours.. Mn2+ , Ni2+, Cr2+, Co2+.. I am using different books to revise some are really old and have completely confused me as they contain conflicting info regarding colours of these compounds e.g. with excess NH3 :s-smilie:

Reply 98

nmudz_009

Original post by giraffegiraffe

Yess i think the main one to be aware of is the Pt.... one :smile:

Thanks

Reply 99

nmudz_009

Whats the colour of the solution made when hexa aqua chromium(iii) is dissolved in excess ammonia? My book says actually says yellow solution, but in my class notes ive got it written as purple :s-smilie:

can anyone confirm