LABORATORY MANUAL: COMPLEXOMETRIC ANALYSIS
Course Code: CHB-302-P • B.Sc. Semester III
Physical and Volumetric Practical Records
EXPERIMENTAL SECTION - 01
Objective: To determine the total amount (in g/L) of MgSO4 in the given solution by using standard EDTA
solution.
Core Parameters:
• Molecular Weight of MgSO4·7H2O: 246.5
• Concentration of EDTA solution provided: M/50 (0.02 M)
Theory:
This analysis is fully based on complexometric titration methods. The total amount of Mg2+ ions can directly
determined by using EDTA as a strong chelating/complexing agent.
A suitable metal ion indicator, mostly Solochrome black or Eriochrome black T (EBT), are used with EDTA which
help for understanding the exact end point of titration process.
The metal ion solution (like aq. MgSO4·7H2O) whose concentration needs to find is first made alkaline by adding
ammonium buffer mixture (aq. NH3 + NH4Cl) to maintaining the pH strictly in the range of 7 to 11. After adding a
small pinch of EBT indicator, the mixture are titrated with known EDTA solution. In starting, metal ions easily
form 1:1 complex with both EDTA and EBT. Here, the Mg-EDTA complex is completely colorless, but Mg-EBT
complex showing a distinct wine-red color (which is slightly less stable than the former).
Note: Therefore, the wine-red color observed in the conical flask is entirely due to the presence of Mg-EBT
complex.
When EDTA solution is dropped from the burette into this mixture, the remaining free Mg2+ ions reacts with
EDTA to make 1:1 stable complex. After the completion of reaction with all free Mg2+ ions, the EDTA starts
displacing the indicator anions from the weaker Mg-EBT complex. This results in the formation of highly stable
Mg-EDTA complex, and the color of titrating system changes from wine-red to a sharp blue color at the end point.
CHB-302-P | B.Sc. III Sem Practical Page 1
, Procedure:
1. Exactly 10ml of the given MgSO4·7H2O sample solution is taken inside a clean conical flask with help of a
pipette. Then, 2ml of ammonium buffer solution and one small pinch of EBT indicator powder was added into
it.
2. The color of the solution becomes deep wine-red immediately after mixing properly.
3. This colored solution was then carefully titrated against the known strength M/50 EDTA solution (filled inside
the burette) until the wine-red color completely turns into blue.
4. Repeat this titration process multiple times to getting at least three concordant readings.
CHB-302-P | B.Sc. III Sem Practical Page 2
Course Code: CHB-302-P • B.Sc. Semester III
Physical and Volumetric Practical Records
EXPERIMENTAL SECTION - 01
Objective: To determine the total amount (in g/L) of MgSO4 in the given solution by using standard EDTA
solution.
Core Parameters:
• Molecular Weight of MgSO4·7H2O: 246.5
• Concentration of EDTA solution provided: M/50 (0.02 M)
Theory:
This analysis is fully based on complexometric titration methods. The total amount of Mg2+ ions can directly
determined by using EDTA as a strong chelating/complexing agent.
A suitable metal ion indicator, mostly Solochrome black or Eriochrome black T (EBT), are used with EDTA which
help for understanding the exact end point of titration process.
The metal ion solution (like aq. MgSO4·7H2O) whose concentration needs to find is first made alkaline by adding
ammonium buffer mixture (aq. NH3 + NH4Cl) to maintaining the pH strictly in the range of 7 to 11. After adding a
small pinch of EBT indicator, the mixture are titrated with known EDTA solution. In starting, metal ions easily
form 1:1 complex with both EDTA and EBT. Here, the Mg-EDTA complex is completely colorless, but Mg-EBT
complex showing a distinct wine-red color (which is slightly less stable than the former).
Note: Therefore, the wine-red color observed in the conical flask is entirely due to the presence of Mg-EBT
complex.
When EDTA solution is dropped from the burette into this mixture, the remaining free Mg2+ ions reacts with
EDTA to make 1:1 stable complex. After the completion of reaction with all free Mg2+ ions, the EDTA starts
displacing the indicator anions from the weaker Mg-EBT complex. This results in the formation of highly stable
Mg-EDTA complex, and the color of titrating system changes from wine-red to a sharp blue color at the end point.
CHB-302-P | B.Sc. III Sem Practical Page 1
, Procedure:
1. Exactly 10ml of the given MgSO4·7H2O sample solution is taken inside a clean conical flask with help of a
pipette. Then, 2ml of ammonium buffer solution and one small pinch of EBT indicator powder was added into
it.
2. The color of the solution becomes deep wine-red immediately after mixing properly.
3. This colored solution was then carefully titrated against the known strength M/50 EDTA solution (filled inside
the burette) until the wine-red color completely turns into blue.
4. Repeat this titration process multiple times to getting at least three concordant readings.
CHB-302-P | B.Sc. III Sem Practical Page 2
