Through repetition.

There's no good mnemonics for the complex ions because there are just too many to remember - everybody has their own little methods. You are better off remembering which ions are 2+ (Cu, Co, Fe) and which ones are 3+ (Al, Cr, Fe) then remembering which ones have special reactions with NH3 (Cu, Cr, Co) and the ones that have special reactions with OH- etc.

Reply 1865

TheTeresaLover

Yes I agree with you. I was so confident about nailing CHEM4 but when I gave the paper I felt like killing myself! Let's hope tomorrow is not too hard! And yeah, BIOL5 better be good this time too! Lol!

Reply 1866

shamk123

i come to this page after finishing my maths c3, which was stupid hard compared to 2015 backwards, knowing ive done no revision for this in the past 7 weeks due to being rimmed by as resits.i HOPE i can can remember all this in one day.

if the papers as hard as chem4 ill eat my paper in the exam

Reply 1867

minjinoor

Original post by shamk123

lool this is literally me
i need 100 in this paper or i've got no chance of a decent A after chem 4

Reply 1868

thenextchemist

What exactly do we have to know about metal extraction for this unit because I kinda forgot my AS stuff?

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Reply 1869

anonymous-97

hi guys does anyone know how to get round thermodynamics im really struggling with it especially with the rearranging the born haber cycle ?

thanks in advance

Reply 1870

26december

Original post by The Informant

How has everyone learned the colours and equations?

The only way you really can learn is through repetition - it gets very boring but on some past papers there have been like 12 marks for this section which can easily boost a grade!

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Reply 1871

26december

Original post by anonymous-97

hi guys does anyone know how to get round thermodynamics im really struggling with it especially with the rearranging the born haber cycle ?

thanks in advance

Try to remember that enthalpy of formation equals the rest of the cycle and then can work out the values and work out the differences

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Reply 1872

nutcase13

Original post by 26december

Try to remember that enthalpy of formation equals the rest of the cycle and then can work out the values and work out the differences

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when talking about [Al(oh)]4-, do you write it as that or as [Al(OH)4(H20)2]4- ?

Reply 1873

26december

Original post by nutcase13

when talking about [Al(oh)]4-, do you write it as that or as [Al(OH)4(H20)2]4- ?

It's not 4- it only has 1 minus
[Al(H2O)2(OH)4]- with XS OH-

For others though I always put 2+, 2-, 3+ etc. outside the bracket

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Reply 1874

chzm

Original post by rolla01

[Cr(OH)6]^3– --> CrO4^2- + 2H2O + 2H+ + 3e- x2
H2O2 + 2e- --> 2OH- x3

these are the two half equations

3H2O2 + 2[Cr(OH)6]^3– --> 6OH- + 2CrO4^2- + 4H2O + 4H+

The OH- and H+ cancel out to make H2O, so 4H+ + 4OH- --> 4H2O
3H2O2 + 2[Cr(OH)6]^3– --> 2OH- + 2CrO4^2- + 8H2O

Hopefully this helped, if you still don't understand here is a useful link: http://www.chemguide.co.uk/inorganic/redox/equations2.html

brilliant thank you! i forgot that you can form water with the H+ and OH-

Reply 1875

Crankyla

I think it is supposed to be [Al(OH)4(H2O)2]-. At least, that's how I've always written it.

Also, I'm unclear on the 'why' of substitution reactions. For example, [Cu(H2O)6]2+ reacts with an excess of ammonia, it forms [Cu(H2O)2(NH3)4]2+. When my class asked our Chemistry teacher why that happens and why aren't all the H2O ligands replaced, all she said was "It just does". Can someone explain it, please??

Reply 1876

nutcase13

Original post by 26december

It's not 4- it only has 1 minus
[Al(H2O)2(OH)4]- with XS OH-

For others though I always put 2+, 2-, 3+ etc. outside the bracket

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ah thanks

Reply 1877

thehollowcrown

Does aluminium oxide or silicion dioxide have the higher melting point?

Reply 1878

nutcase13

Original post by thehollowcrown

Does aluminium oxide or silicion dioxide have the higher melting point?

aluminium oxide

Reply 1879

shiney101

When they ask why a coloured ion is formed do you say the d-electrons absorb visible light or white light? I've always said it's visible light but then in one of the 2010 papers it said white light so now i'm not sure.