|Possible precipitates are: Al(OH)3, Cr(OH)3,
FeS, Fe2S3, MnS, ZnS, NiS and CoS. Add 1 mL
of Na2SO4 and 1 mL of NaHSO4 to act as
a buffer (reaction #17)
|Precipitate:Possibly ZnS, CoS or NiS Add dilute HCl,
stir and filter if necessary. (reaction
|Precipitate: NiS or CoS. Add HCl and NaOCl and
boil. Let cool and divide into 2 parts. (reaction
Add NH4OH until basic to litmmus and add 2 mL of dimethylgloxime
A red precipitate confirms the presence of Ni2+.
Add HCl until acidic to litmus. Add 2 mL of alpha
A red precipitate confirms Co2+.
|Filtrate: Add NaOH until basic to litmus. Add H2S
A white or grey precipitate confirms the presence of Zn2+.
|Filtrate: Possibly Al3+, Cr3+,
Fe2+, Fe3+, Mn2+.
Boil to remove the H2S. Add 5-8 drops of 30% H2O2
and 5 mL of NaOH. Let stand for 5 minutes. Boil to remove any
excess H2O2. (reaction
|Filtrate:Add HCl until the solution is acidic.
Add just enough NH4OH to precipitate the Al(OH)3
Filter if necessary. (reaction
Al(OH)3. Add HCl to redissolve the precipitate.
Add 1 mL of the aluminon reagent. Add NH4OH to cause reprecipitation.
A red-dyed precipitate confirms the Al3+ ion. (reaction
Possibly the CrO42- ion.
Add acetic acid until the solution is acidic to litmus. Add
A yellow precipitate confirms the presence of Cr3+ ion.
Possibly Fe(OH)2, Fe(OH)3 or MnO2.
Divide into three parts and go to the Fe2+, Fe3+
and Mn2+ tests below.
|Fe2+ Test Add NH4OH to just
dissolve the precipitate. Add 2 mL of potassium ferricyanide.
A dark blue precipitates indicates Fe2+. (If the Fe3+
test is negative then Fe2+ is confirmed)
||Fe3+ Test Add NH4OH to dissolve
the precipitate. Acidify with HCl. Add 2 mL of KCNS.
A red complex of FeCNS2+ confirms the presence of the
|Mn2+ Test: Add concentrated HNO3,
H2O2 and boil to convert the MnO2 to Mn2+.
Allow to cool. Add 2 mL of NaBiO2, sodium bismuthate.
A purple solution of MnO41- ions confirms the presence
of the Mn2+ ion.