Determine the molarity of the given KMnO, solution with the help of supplied 20 Mohr's salt solution.
Answers
Answer:
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Explanation:
Aim:
To determine the strength of a given potassium permanganate solution against standard ferrous ammonium sulfate (Mohr’s salt) solution.
Theory:
Potassium permanganate is a strong oxidant in the presence of sulfuric acid. Mohr salt is a double salt forming a single crystalline structure having the formula (NH4</sub2SO4. FeSO4. 6H2O. The chemical name for Mohr’s salt is ferrous ammonium sulfate
In this titration Mohr salt acts as a reducing agent and potassium permanganate acts as an oxidising agent. So the reaction between Mohr’s salt and potassium permanganate is a redox reaction. In this redox reaction, ferrous ion from Mohr’s salt gets oxidised and pink coloured of manganese present in potassium permanganate which is in the +7 oxidation state gets reduced to colourless Mn2+ state.
Reduction half reaction –
2KMnO4 + 3H2SO4 → K2SO4 + 2MnSO4 + 3H2O + 5[O]
Oxidation half reaction –
2FeSO4(NH4)2SO4.6H2O + H2SO4 + 5[O] → Fe2(SO4)3 + 2(NH4)2SO4 + 13H2O x 5
Overall reaction –
2KMnO4 + 10FeSO4(NH4)2SO4.6H2O+8H2O → K2SO4+ 2MnSO4+ 5Fe2(SO4)3+ 10(NH4)2SO4+ 68H2O
This titration is based upon oxidation-reduction titrations. When ferrous ammonium sulfate solution is titrated against potassium permanganate in the presence of acidic medium by sulfuric acid. Acidic medium is necessary in order to prevent precipitation of manganese oxide. Here KMnO4 acts as a self indicator and this titration is called permanganate titration.
Materials Required:
Mohr’s salt (ferrous ammonium sulfate) ,Potassium permanganate solution , Dilute sulfuric acid , Chemical balance ,Burette , Burette stand, Pipette , Conical flask, Funnel , Measuring flask , Weighing bottle , White tile , Burnet , Wire gauze
Apparatus Setup:
In burette – KMnO4 solution
In Conical flask – 10ml of Ferrous Ammonium Sulfate (Mohr’s salt) + Sulfuric acid
Indicator – Self indicator (KMnO4)
End Point – Colourless to permanent pale pink colour.
Procedure:
(a) Preparation of 0.05M standard solution of ferrous ammonium sulfate:
The quantity of Mohr’s salt required for the 250ml of the solution having a normality of 0.05N can be calculated as follows.
The molar mass of mohr’s salt = 392 g/mol
Strength = Normality x Equivalent weight
= (1/20) x 392 = 19.6 g/L
For preparing 250ml of N/20 Mohr’s salt solution, Mohr salt required
= (19.6/1000) x 250 = 4.9 gm
Weigh an empty watch glass using a chemical balance.
Weigh accurately 4.9gm of Mohr’s salt in a chemical balance.
With the help of a funnel transfer the Mohr’s salt into the measuring flask.
Now wash the funnel with distilled water without removing the funnel from the flask.
Make the solution up to the marked point with distilled water and make sure the Mohr’s salt is fully dissolved.
This solution is 0.05N standard solution of Mohr’s salt.
(b) Titration of potassium permanganate solution against standard ferrous ammonium sulfate (Mohr’s salt) solution:
Wash and rinse the burette and pipette with distilled water and then rinse with the corresponding solution to be filled in them.
Rinse the burette with the potassium permanganate solution and fill the burette with potassium permanganate solution.
Fix the burette in the burette stand and place the white tile below the burette in order to find the endpoint correctly.
Rinse the pipette and conical flask with standard ferrous sulfate solution.
Pipette out 10ml of 0.05N standard Mohr’s salt solution into the conical flask.
Add a test tube full of sulfuric acid in order to prevent oxidation of manganese to form manganese dioxide.
Note down the initial reading in the burette before starting the titration.
Now start the titration, titrate against potassium permanganate solution and simultaneously swirl the solution in the flask gently.
Initially, the purple colour of KMnO4 is discharged with ferrous ammonium sulfate. The appearance of a permanent pink colour reveals the endpoint.
Repeat the titration until concordant values are obtained.
Note down the upper meniscus on the burette readings.
Record the reading in the observation table given below in order to calculate the molarity of KMnO4 given.
Calculations:
(a) Normality of KMnO4 solution:
Consider y ml of given KMnO4 solution are equivalent to 20ml of N/10 Mohr’s salt solution.
According to law of equivalents,
N1V1 = N2V2
N1, N2 are normality of Mohr’s salt and KMnO4 solution respectively.
V1, V2 are volume of Mohr’s salt and KMnO4 respectively.
1/10 x 20 = N2 x y
N2 = 2/y
N = Normality of given KMnO4 solution = 2/y
(b) Strength of KMnO4 solution:
Strength = Normality x Equivalent mass
Equivalent mass of KMnO4 =
= 158/5
= 31.6
= 2/y x 31.6 g/liter
Molarity of KMnO4 solution
N = M x Number of electron gained
N = M x 5
M = N/5 moles/ litre
The strength of and molarity of given KMnO4 solution is found out as 2/y x 31.6 g/l and N/5 moles/liter respectively.