Question

design a seperation scheme for group of cations Al3+,Ba2+,Cu2+,Ni2+

Answer 1

First, catalogue the metals:

Al3+ = Group III cations

Ba2+ = Group IV cation

Cu2+ = Group II cations

Ni2+ = Group III cation

Then...

Easiest to separate: Cu2+

Will precipitate as CuS(s) when:

H2S(aq) is added in ACIDIC solution/media

so

Cu2+(aq) + S-2(aq) = CuS(s)

For Nickel:

Add NaOH at 4M, in addition with H2O2; this iwll only precipitate Ni(OH)2(s) and let Al(OH)4- complex of Aluminium

Filtrate solid which is Nickel, then the auqeous solution contains only Al(OH)4- ions,

For Nickel precipitate, add dimethylglyoxime (DMG) in basic media:

Ni(NO3)2 + 2 HDMG = Ni(DMG)2 + 2 HNO3

this should turn RED-Strawberry colored... this will now be

For Al3+:

Add concentrated acetic acid, which is a weak acid, but will set pH in a buffer media

this will make Al(OH)4- complex to preciptiate with the Red dye (aluminon)

The process:

red dye aluminon (aurin tricarboxylic acid) by aluminum hydroxide as the Al(OH)3 precipitates.

Finally, Ba2+

Add CO3- ions

Ba2+ + CO3- = BaCO3(s)

this is a solid precipitate, filter and you are good to go