To find the Molarity and Strength of the given KMnO4 solution using M/20 standard Mohr’s Salt Solution

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AIM: To find the molarity and strength of the given KMnO₄ solution using M/20 standard Mohr’s salt solution.

APPARATUS REQUIRED:

• Burette
• Pipette
• Iron stand
• Conical flask
• Test tube
• Test tube holders

CHEMICALS REQUIRED:

• KMnO₄ solution
• M/20 Mohr’s Salt Solutions
• Distilled water
• 4N H₂SO₄

THEORY:

The reaction between KMnO₄ and Mohr’s Salt is a redox reaction in which KMnO₄ acts as an oxidizing agent oxidizes the Fe²⁺ ions to Fe³⁺ ions in acidic medium. The end of the reaction is indicated by the appearance of light pink color.

INDICATOR USED: KMnO₄ is a self-indicator.

END POINT: Colorless to light pink.

CHEMICAL EQUATIONS:

2KMnO₄ + 3H₂SO₄ --> K₂SO₄ +2MnSO₄ + 3H₂O +5[O]

{2FeSO₄(NH₄)2SO₄.6H₂O + H₂SO₄ + [O] --> Fe₂(SO₄)₃ + 2(NH₄)SO₄ + 3H₂O} X 5, multiplying it by 5

Adding both the equations,

2KMnO₄ + 8H₂SO₄ + 10FeSO₄(NH₄)₂SO₄.6H₂O --> K₂SO₄ + 2MnSO₄ + 5Fe₂(SO₄)₃ + 10(NH₄)₂SO₄ +18H₂O

IONIC EQUATIONS:

MnO₄^- + 8H⁺ + 5e^- --> Mn²⁺ + 4H₂O

{Fe²⁺ --> Fe³⁺ +e^-} X 5, multiplying it by 5

Adding both the equations,

MnO₄^- +8H⁺ + 5Fe²⁺ --> 5Fe³⁺ +Mn²⁺ + 4H₂O

PROCEDURE:

The burette is first rinsed with distilled water and then the given KMnO₄ solution. It is then filled with KMnO₄ solution, taking care to see that no air bubble is present in the burette. The level of the KMnO₄ solution is adjusted until it coincides the upper level with the zero mark on the burette. The pipette is rinsed with water and 20ml of Mohr’s salt solution is pipetted out into the clean volumetric flask. Approximately 3/4^th test tube full of 4N H₂SO₄ is added to the solution in the titration flask. The nozzle of the burette should remain in the neck of the flask. The flask is swirled gently at regular intervals and the solution is added till a light pink color appears in the flask. The final reading is noted. The entire process is repeated until a set of three concurrent reading are obtained.

OBSERVATION:

Volume of Mohr’s salt pipetted =20ml

Molarity of Mohr’s salt solution = 0.05M

Serial Number	Volume of Mohr’s Salt Solution taken	Volume of KMnO4 added.		Volume of KMnO4 used
		Initial Volume	Final Volume
1	20	0	19.1	19.1
2	20	19.1	38.1	19.0
3	20	0	19.0	19.0
		Concordant Reading-->		19.0

(a table showing a set of example values to be found out in the practical classes)

CALCULATIONS:

Mohr’s Salt <-- KMnO₄

(M₁V₁)/N₁  =  (M₂V₂)/N₂

M₁ – Molarity of Mohr’s Salt Solution = 0.05M

V₁ – Volume of Mohr’s Salt Solution = 20ml

N₁ – Number of moles of Mohr’s Salt Solution = 10

M₂ – Molarity of KMnO₄ solution = M₂

V₂ – Volume of KMnO₄ solution = 19 (This is supposed to be the Concordant Reading)

N₂ – Number of moles of KMnO₄ Solution = 2

Solving the equation with the given values,

M₂ = 0.0105M

Strength of KMnO₄ solution in gm/L is,

= Molarity X Molecular Mass

= M₂ X 158 = 0.0105 X158 = 1.66gm/L

INFERENCE:

1. Molarity of KMnO₄ solution is 0.01M.
2. The strength of given KMnO₄ solution is 1.58gm/l.

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To know more click on the articles below (Important for Boards):-

• To prepare 250ml of M/20 standard Mohr’s Salt solution.
• How to find out the Mass of Salt required to achieve therequired Concentration of a Solution
• Apparatus Used in Volumetric Analysis
• Some important terms related to concentrations of solutions
• Equivalent masses of oxidizing and reducing agents
• Preparing a standard solution
• Viva Questions related to Volumetric Analysis

Reference:-

• Verma, Dr. N.K.. Comprehensive Practical Chemistry, Class XII.
• NCERT. Chemistry Part I and II, Class XII.

For latest syllabus, both theory and practical papers for class XII, check out the CBSE’s official site http://cbseacademic.in/ for more info.

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Related Questions-

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