SCH4C  Qualitative Analysis - Group 3 Analysis Separation Table 
                                            The Alkaline Hydrogen Sulphide Group
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 #18)
 
Precipitate: NiS or CoS.  Add HCl and NaOCl and boil.  Let cool and divide into 2 parts. (reaction #18b)
Part 1
Add NH4OH until basic to litmmus and add 2 mL of dimethylgloxime reagent.

A red precipitate confirms the presence of Ni2+
(reaction 19a)

Part 2
Add HCl until acidic to litmus.  Add 2 mL of alpha
-nitroso
-beta
-napthol.
A red precipitate confirms Co2+.
(reaction 19b)
Filtrate: Add NaOH until basic to litmus.  Add H2S gas.
A white or grey precipitate confirms the presence of Zn2+.
(reaction #20)
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 #21)
Filtrate:Add HCl until the solution is acidic.  Add just enough NH4OH to precipitate the Al(OH)3 if present.
Filter if necessary.  (reaction #25)
Precipitate:
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 #26)
Filtrate:
Possibly the CrO42- ion. 
Add acetic acid until the solution is acidic to litmus.  Add lead(II) acetate.  
A yellow precipitate confirms the presence of Cr3+ ion.
(reaction #27)
Precipitate:
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 Fe3+ ion.  
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.

         Previous  Next   Return to the Lab Menu    Return to the SCH4C Main Menu

Copyright 1997, 2002, 2003  Tom Stretton (stretton@ripnet.com) Updated August, 2002 ts.