CATION ANALYSIS

Question 1

How is the original solution prepared and what are the reagents in order used ?

Answer 1

200-300 mg of sample is dissolved in water/hot water/dil.Hcl/conc.HCl/dil.HNO3/conc.HNO3 / Aqua regia.

Question 2

What are the notes with regard to conc. HCl and aqua regia?

Answer 2

1. excess conc. HCl should be evaporated and diluted with water.
2. Aqua regia should be evaporated to dryness and conc. HNO3 should be added and diluted.

Question 3

give the test for group 1 cation .

Answer 3

Dil. HCl is added to the original solution . If ppt is formed then excess HCl is added to complete precipitation . the centrifuge is boiled and washed.
for Pb2+ and Ag+.

Question 4

Give the test for group 2a cation.

Answer 4

To the centrifugate/o.s , dil.HCL is added and 4 drops of 3% H2O2 solution is added and the mixture is heated in a water bath . Through this H2S gas is passed and if ppt forms it is washed with NH4NO3 and centrifuged again . To the residue 2 ml of NAOH and ammonium polysulfide is added.
black : Pb2+/Cu2+ ; yellow: Cd2+

Question 5

Give the test for group 2b cation.

Answer 5

To the centrifugate from group 2a , dil. HCl is added till acidic. brown ppt : Sn2+ .

Question 6

Give the test for group 3a

Answer 6

To the original solution, dil HCl is added and NH4Cl is added(50-100 mg) , It is heated in a water bath , stirred, and NH4OH is added till alkaline. It is boiled and centrifuged.
green: Cr3+ reddish-brown: Fe3+

Question 7

Give the test for Group 3b

Answer 7

To the centrifugate from group 3a, excess NH4OH is added and H2S is passed through the solution.
Black: Ni2+ White:Zn2+ pink:Mn2+

Question 8

Give the test for group 4

Answer 8

To the centrifugate from group 3b , H2S is evaporated and 1 ml of (NH4)2CO3 is added . After that 2 drops of NH4OH is added and warmed gently .
If white precipitate is observed, then Ba2+,Sr2+ and Ca2+ could be present .