Here I am explaining , how to do Titration of Mohr’s salt (Ferrous ammonium sulphate) with KMnO4 solution. The solution whose concentration is known is called standard solution. The concentration of solution which has to be determined is called unknown solution .Unknown solution is added slowly to a certain volume of the standard solution. As the reaction is complete, the colour changes (end point).The volume of the unknown solution used is now known. Using the law of equivalents (n1×M1×V1 = n2×M2×V2) find the molarity and also strength of the unknown solution. This process is called titration.
Experiment No. 1
Objective :- To determine the strengh of a given potassium permanganate solution against a 0.05M standard ferrous ammonium sulphate (Mohr’s salt) solution
Apparatus and materials required : Burette, pipette, conical flask, measuring flask, oxalic acid, KMnO4 solution, burner, distilled water etc.
Principle :– Amount of solid ferrous ammonium sulphate(w) required to prepare a 250 mL, 0.05M standard solution
w =(Molecular weight × molarity × Volume) /1000
w =(392×0.05×250)/1000
w = 4.9 gram
Weigh 4.9 g of mohr’s salt on a weighing tube and dissolve it in 250mL of distilled water in a conical flask and add a little amount of concentrated H2SO4 to prevent hydrolysis. When a solution with a concentration of 0.05M ferrous ammonium sulphate is titrated with a KMnO4 solution, the following reaction occurs:
2KMnO4 + 3H2SO4 → K2SO4 +2MnSO4 +3H2O 5[O]
[ 2FeSO4 +H2SO4 +[O] → Fe2(SO4)3 +H2O ] X 5
or complete reaction can be written as follows-
KMnO4 + 10FeSO4 + 8H2SO4 → K2SO4 +2MnSO4 + 5Fe(SO4)3 + 8H2O
Indicator: KMnO4 is a self indicator.
End point : Colourless to permanent pink
Method :– (1) Weigh 4.9 gram ferrous ammonium sulphate (mohr’s salt) (solid) on a chemical balance.
(2) Pour the weighed quantity into a flask or beakerwith a glass funnel. Add water slowly and add a little amount of concentrated H2SO4.
(3) Fill the given KMnO4 solution in biurrette and note the reading of the solution filled in burette.
(4) Pour the ferrous ammonium solution of 0.05M concentration into the conikal flask with the help of a pipette which is of 25ml.
(5) Now let KMnO4 solution fall from the burette drop by drop into the ferrous ammonium solution in the conical flask until the solution becomes permanently light pink. Keep stirring the flask during this time.
(6) Repeat this experiment 3-4 times til you get two same readings
Observation :- (1) Approximate weight of weighing tube = 7.8 g
(2) Weight of weighing tube + mohr’s salt = 12.7 g
(3) Correct weight of empty weighing tube = 7.8842 g
(4) Weight of mohr’s salt = 4.9 g
(5) Volume of pipette = 25mL
| S.No. | Oxalic acid | Reading of Burrette (Initial) | Reading of Burrette (Final) | used KMnO4 |
|---|---|---|---|---|
| 1 | 25 mL | 0.00 mL | 8.5 mL | 8.5 mL |
| 2 | 25 mL | 0.00 mL | 8.3 mL | 8.3 mL |
| 3 | 25 mL | 0.00 mL | 8.3 mL | 8.3 mL |
KMnO4 used =8.3 mL (same readings)
Calculations: – N1×V1 (KMn04) =N2×V2 (mohr’s salt solution)
n1×M1×V1(KMn04)= n2×M2×V2(oxalic acid)
5×M1×8.3 = 1×(0.05) ×25
M1 = 0.03 mol/L
Strength of the given KMnO4 solution = Molarity x Molecular mass
= 0.03 x 158
= 4.74 gram/Litre
Result :- Strength of the given KMnO4solution = 4.74 gram/Litre
Precautions:-
(1) The funnel (funnel) should be removed from the top of the burette while doing the measurement.
(2) The conical flask should be rinsed with an mohr’s salt solution.
(3) There should be no air bubbles in the burette jet.
(4) The liquid left in the tip of the pipette should not be removed by blowing because it is more than the prescribed volume.
Experiment No. 2
Objective :- To determine the strengh of a given potassium permanganate solution against a M/25 standard ferrous ammonium sulphate (Mohr’s salt) solution
Apparatus and materials required : Burette, pipette, conical flask, measuring flask, oxalic acid, KMnO4 solution, burner, distilled water etc.
Principle :– Amount of solid ferrous ammonium sulphate(w) required to prepare a 250 mL, M/25 standard solution
w =(Molecular weight × molarity × Volume) /1000
w =(392× 1/25 ×250)/1000
w = 3.92 gram
Weigh 3.92 g of mohr’s salt on a weighing tube and dissolve it in 250mL of distilled water in a conical flask and add a little amount of concentrated H2SO4 to prevent hydrolysis. When a solution with a concentration of M/25 ferrous ammonium sulphate is titrated with a KMnO4 solution, the following reaction occurs:
2KMnO4 + 3H2SO4 → K2SO4 +2MnSO4 +3H2O 5[O]
[ 2FeSO4 +H2SO4 +[O] → Fe2(SO4)3 +H2O ] X 5
or complete reaction can be written as follows-
KMnO4 + 10FeSO4 + 8H2SO4 → K2SO4 +2MnSO4 + 5Fe(SO4)3 + 8H2O
Indicator: KMnO4 is a self indicator.
End point : Colourless to permanent pink
Method :– (1) Weigh 3.92 gram ferrous ammonium sulphate (mohr’s salt) (solid) on a chemical balance.
(2) Pour the weighed quantity into a flask or beakerwith a glass funnel. Add water slowly and add a little amount of concentrated H2SO4.
(3) Fill the given KMnO4 solution in biurrette and note the reading of the solution filled in burette.
(4) Pour the ferrous ammonium solution of 0.05M concentration into the conikal flask with the help of a pipette which is of 25ml.
(5) Now let KMnO4 solution fall from the burette drop by drop into the ferrous ammonium solution in the conical flask until the solution becomes permanently light pink. Keep stirring the flask during this time.
(6) Repeat this experiment 3-4 times til you get two same readings
Observation :- (1) Approximate weight of weighing tube = 7.8 g
(2) Weight of weighing tube + mohr’s salt = 11.72 g
(3) Correct weight of empty weighing tube = 7.8842 g
(4) Weight of mohr’s salt = 3.92 g
(5) Volume of pipette = 25mL
| S.No. | Oxalic acid | Reading of Burrette (Initial) | Reading of Burrette (Final) | used KMnO4 |
|---|---|---|---|---|
| 1 | 25 mL | 0.00 mL | 5.7 mL | 5.7 mL |
| 2 | 25 mL | 0.00 mL | 5.8 mL | 5.8 mL |
| 3 | 25 mL | 0.00 mL | 5.8 mL | 5.8 mL |
KMnO4 used =5.8 mL (same readings)
Calculations: – N1×V1 (KMn04) =N2×V2 (mohr’s salt solution)
n1×M1×V1(KMn04)= n2×M2×V2(oxalic acid)
5×M1×5.8 = 1×(1/25) ×25
M1 = 0.034 mol/L
Strength of the given KMnO4 solution = Molarity x Molecular mass
= 0.034 x 158
= 5.372 gram/Litre
Result :- Strength of the given KMnO4solution = 5.372 gram/Litre
Precautions:-
(1) The funnel (funnel) should be removed from the top of the burette while doing the measurement.
(2) The conical flask should be rinsed with an mohr’s salt solution.
(3) There should be no air bubbles in the burette jet.
(4) The liquid left in the tip of the pipette should not be removed by blowing because it is more than the prescribed volume.