Submission of Proposal under Star College Scheme

QUALITATIVE ASPECTS IN GRAVIMETRIC ANALYSIS
1. REMOVAL OF IMPURITY:
To estimate the given metal ion in the presence of other metal ion as impurity, it is necessary to remove the impurity by precipitating with suitable reagents.

1. 
   Passing of H₂S (jf any): Use a clean glass tube (not glass rod) for passing H2S. (Use beaker for passing H2S gas)
   
2. 
   Time ofpassing H₂S:
   

Not less than 2-3 minutes. The glass tube through which H2S is passed, should be washed with water & the washing must be collected in the beaker.
c. Removal of H₂S and concentration: Remove H₂S completely and concentrate the solution to half of its initial quantity.
2. PRECIPITATION:

1. 
   Precipitating agent:
   

To be added slowly with constant stirring. Add the required quantity as given in procedure.
b) Maintenance of pH:
Proper pH should be maintained as given in the procedure to ensure complete precipitation.
c) Technique:
Use the proper amount of reagent. Precipitant should be added slowly with constant stirring Use sufficient amount of reagent in required quantity as given in the procedure.
3. DIGESTION:

1. 
   Use of water- bath:
   

Digest the ppt. for a given time as mentioned in the chart. During digestion do not remove the glass rod.
b) Completion of precipitation:
After digestion, check complete precipitation by adding some more precipitating agent.
4. FILTRATION:

1. 
   Technique:
   

Precipitate to be filtered through sintered glass crucible using suction pump.

2. 
   Porosity of crucible:
   

Depending on the size of ppt. crucible of the proper porosity_Ooulci be used like G3, G4 as mentioned in the chart.
5. WASHING:

1. 
   Solvent for washing:
   

Depending on the solubility of the ppt, proper wash liquid should be used as given in the chart.
b) Technique:
Do not add wash liquid up to the upper end of the crucible, it should cover 3/4^th of the crucible. Allow the wash liquid to drain as completely as possible before adding next washing.
c) Elimination of CI^- , s0₄^2- PO4^3- :
Check removal of CI^- after 4 washings. Don't check after each Washing. SO4^2- PO4^3-are removed prior to Cl^-therefore, removal of Cl^- ensures removal of SO4^1-8, PO4^3-