APPARTUS REQUIRED:
- Burette
- Conical flask
- Pipette
- Test tube
CHEMICAL REQUIRED:
- KMNO4
- C(COOH)2
- Mohr’s salt solution
- Dilute H2SO4
THEORY:
Ferrous iron is a form of iron that has a positive charge of +2, commonly found in compounds where iron is bonded to other elements. Volumetric analysis is the determination of amount of solute present in solution by moistening volume of solution required to react completely with certain volume of solution of another substance.
Standard solution:
The solution whose strength is provided is known as the standard solution. It consists of two types of solution i.e. primary standard solution and secondary standard solution.
Primary standard solution:
The solution prepared by dissolving known weight of pure and stable solute to the known volume (weight) of the solvent is called primary standard solution.
Primary standard substance:
The substance used to prepare primary standard solution is called primary standard substance.
Secondary standard solution:
The solution which has been standardized with the help of primary standard solution is called secondary standard solution.
Secondary standard substance:
The substance which cannot fulfill criteria of primary standard substance is called secondary standard substance.
Acidimetry:
The process of determining the strength of acid solution by measuring its volume required to react completely with standard alkali solution is known as acidimetry.
Alkalimetry:
The process of determining strength of alkali solution by measuring its volume required to react completely with standard acid solution is known as alkalimetry.
The technique to know the strength of given unknown solution with the help of known standard solution is called as titration. The amount of ferrous ion can be estimated by titrating with standardized KMNO4 solution in acidic medium.
Because of Mohr’s salt solution in acidic medium when KMNO4 solution is:
10 FeSO4 (NH4) SO4.6H2O + 8 H2SO4 + 2KMNO4 →5Fe (SO4)3 + 10 (NH4)2SO4 + K2SO4 + 2MNSO4 + 68H2O
At the end point a permanent point pink color is developed in the solution.
PROCEDURE
First of all, the given apparatus used for titration i.e. burette, pipette, conical flask were cleaned properly with water. Then, the burette was rinsed and was filled with standard KMNO4 solution. 10 ml of Mohr’s salt was pipette out and a test tube of dil. H2SO4 is mixed in a clean beaker. Per magnate solution from the burette was shaken continuously. At this condition burette reading was taken and titration was carried out till the concurrent reading occurred.
OBSERVATION TABLE:
Burette reading standard H2SO4
| S. N. | Volume of Mohr’s salt | initial | final | difference | Concurrent |
| 1. | 10 ml | 0 | 11.7 | 11.7 | |
| 2. | 10 ml | 11.7 | 23 | 11.3 | 11.3 |
| 3. | 10 ml | 23 | 34.3 | 11.3 |
CALCULATION:
Volume of KMNO4 (V1) = 11.3 ml
Strength of KMNO4 (N1) = 0.1 N
Volume of Mohr’s salt (V2) = 10 ml
Strength of Mohr’s salt (N2) =?
Then, N1V1 = N2V2
Or, N2 = 11.3 ml×0.1
10 ml
= 0.113 N
The concentration of dilute Fe2+ solution = 0.113 N
1000ml of 1N Fe2+ solution = 55.8g of Fe2+
10 ml of 0.113N Fe2+ solution = 55.8 × 0.113 × 10
1000
= 0.063 gm of Fe++ in Mohr’s salt
And gm/liter = weight of Mohr’s salt × 1000
Volume of Mohr’s salt
= 0.063×1000
10
= 6.3 gm/liter
RESULT:
From above observation, the amount of iron in Mohr’s salt was found to be 0.061 gm and 6.3 gm/liter.
CONCLUSION:
Hence, amount of iron in Mohr’s salt can be determined by double titration method using solution oxalic acid and Mohr’s salt solution.
PRECAUTION:
- Reading should be noted carefully.
- Chemical should be used carefully.
- Apparatus should be cleaned before and after use.
- Apparatus should be fixed at good point.