Molecular reactions involved when mohr'salt is provided to find the strength, molarity of KMnO4
To find the strength and molarity of KMnO4 using Mohr's salt (ferrous ammonium sulfate, (NH4)2Fe(SO4)2), the following redox reaction takes place:
5Fe2+ + MnO4- + 8H+ → 5Fe3+ + Mn2+ + 4H2O
In this reaction, the Fe2+ ions from Mohr's salt are oxidized to Fe3+ ions, while the permanganate ion, MnO4-, is reduced to Mn2+ ions. The reaction occurs in an acidic medium, represented by the presence of H+ ions.
To determine the strength and molarity of KMnO4, you will need the following information:
1. Volume of Mohr's salt solution used (V1) - measured in milliliters (mL).
2. Volume of KMnO4 solution used (V2) - measured in milliliters (mL).
3. Normality of Mohr's salt solution (N1) - provided or calculated.
4. Normality of KMnO4 solution (N2) - to be determined.
Here's a step-by-step guide to determine the strength and molarity of KMnO4 using Mohr's Salt:
Step 1: Prepare and standardize Mohr's salt solution:
a. Dissolve a known mass of Mohr's salt ((NH4)2Fe(SO4)2) in distilled water to make a known volume of solution.
b. Add a few milliliters of dilute sulfuric acid (H2SO4) to provide an acidic medium.
c. Titrate the prepared Mohr's salt solution with a standard solution of potassium permanganate (KMnO4) until the pinkish color of KMnO4 persists for about 30 seconds. Record the volume of KMnO4 used (V2, in mL).
d. Repeat the titration at least three times and calculate the average volume of KMnO4 used.
Step 2: Calculation of the normality of Mohr's salt solution (N1):
a. The normality is calculated using the formula:
N1 = N2 × V2 ÷ V1
(Where N2 is the known normality of KMnO4 solution, V2 is the average volume of KMnO4 solution used, and V1 is the volume of Mohr's salt solution used.)
Step 3: Determining the normality and molarity of KMnO4:
a. Using the balanced redox equation, determine the mole ratio between Mohr's salt (Fe2+) and KMnO4 (MnO4-).
b. Since the normality of Mohr's salt solution (N1) is now known, equate the moles of Fe2+ and MnO4- by multiplying their respective mole ratios by N1.
c. The normality and molarity of KMnO4 will be the same as N1 since the number of moles is equated.
Remember to follow appropriate safety precautions while handling chemicals and conducting experiments.