Titration |Oxalic Acid Vs KMnO4 | Mohr Salt Vs KMnO4 | Calculations | Chemistry Practical

Chemistry Practical Class 12: Titration of KMnO4 with Oxalic Acid

Introduction to the Experiment

• The video introduces Saurabh Raina discussing the chemistry practical for class 12, focusing on two experiments involving KMnO4 and oxalic acid, as well as KMnO4 and mohar salt.

• It highlights that these titrations involve redox reactions where oxidation and reduction occur in an aqueous solution through electron transfer.

Redox Reaction Details

• The reaction involves potassium permanganate (KMnO4), a powerful oxidant that gets reduced in acidic medium to Mn²⁺. The oxidation number changes from +7 to +2 during this process.

• To balance the reaction, four water molecules (H₂O) are added, along with eight hydrogen ions (H⁺), resulting in a total charge balance by adding five electrons.

Preparation of Solutions

• Dilute H₂SO₄ is used instead of nitric acid because nitric acid itself acts as an oxidizing agent.

• Oxalic acid and mohar salt serve as reducing agents in the experiment. A standard solution of 100 mL of M/20 oxalic acid is prepared for titration.

Calculating Molarity and Mass

• The molecular formula for oxalic acid is given as C₂H₂O₄·2H₂O, with a molar mass of 126 g/mol.

• To prepare a 1/20 molar solution, calculations are made to determine how much oxalic acid is needed; it results in needing approximately 0.63 grams for the preparation.

Preparing Standard Solution

• A watch glass is used to weigh out 0.63 g of oxalic acid accurately before transferring it into a standard flask using a funnel.

• Distilled water is added up to the mark on the flask to ensure complete dissolution of oxalic acid before shaking thoroughly.

Conducting the Titration

• Potassium permanganate solution is rinsed into a burette after ensuring no air bubbles are present.

• A conical flask containing 10 mL of prepared oxalic acid solution mixed with dilute H₂SO₄ is heated between 50°C - 60°C to speed up the reaction rate.

Observing Color Change During Titration

• An initial reading of KMnO₄ volume in the burette is noted before slowly adding it to the conical flask while swirling.

• As KMnO₄ reacts with oxalic acid, its violet color disappears indicating completion; if excess KMnO₄ causes light pink coloration, this signals reaching endpoint.

Final Steps and Repetition

• The final volume readings (V2 - V1 = titration result) must be recorded accurately for analysis; this process should be repeated for consistency in results.

Preparation and Titration of Oxalic Acid Solution

Steps for Preparing the Experiment

• The procedure involves adding 10 mL of oxalic acid solution to a conical flask, followed by the addition of H₂SO₄ and heating. Readings will be taken from V2 to V3, ensuring three concordant readings that should match.

• For burette readings, the upper meniscus is considered. Three serial readings are required, with each reading noting the volume of oxalic acid used as 10 mL.

• The volume of KMnO₄ used is calculated as V2 - V1. All three readings must yield the same value (X). The redox reactions involving MnO₄⁻ and oxalic acid will be written down.

Understanding Redox Reactions

• In the reduction half-reaction, MnO₄⁻ gains electrons in an acidic medium (8 H⁺ + 5 e⁻ → Mn²⁺ + 4 H₂O).

• The oxidation half-reaction involves oxalate ions (C₂O₄²⁻), which convert into CO₂ while losing two electrons. This establishes its role as a reducing agent.

Calculating Molarity and Strength

• The n-factor for KMnO₄ is five since it gains five electrons; for C₂O₄²⁻, it’s two as it loses two electrons. Molarity calculations involve substituting values from concordant readings.

• To find the strength of KMnO₄ in grams per liter, multiply its molarity by its molar mass (158 g/mol).

Preparation of Standard Solutions

• A standard solution of ferrous ammonium sulfate (Mohr's salt), with a molar mass of 392 g/mol, needs to be prepared at a concentration of 0.1 M.

• To prepare this solution: calculate moles using mass divided by molar mass and adjust volume to liters accordingly. For example, use 3.92 g for preparation in a total volume of 100 mL.

Conducting Titration

• Transfer the prepared Mohr's salt solution into a standard flask using distilled water to ensure complete dissolution up to the mark.

• Rinse the burette with KMnO₄ solution before filling it. Take care to remove air bubbles during titration.

Observations During Titration

• Add 10 mL of Mohr's salt solution into a conical flask along with dilute H₂SO₄ without heating since it's not required due to fast reaction kinetics.

• As KMnO₄ is added during titration, observe color changes until reaching endpoint where permanent pink indicates completion due to excess KMnO₄.

Finalizing Results

• Repeat titrations until three concordant results are obtained for accuracy in measurements (V2 - V1).

• Record initial and final volumes carefully; ensure consistency across all trials for reliable data collection on redox reactions between Fe²⁺ and MnO₄⁻ ions.

This structured approach provides clarity on conducting experiments involving redox reactions between oxalic acid and potassium permanganate while emphasizing accurate measurement techniques essential in analytical chemistry practices.

Understanding Molarity and Strength of KMnO4 Solution

Calculation of Molarity

• The discussion begins with the calculation of molarity for a solution, denoted as m_1 , where the volume is represented by x .

• It is established that there is one electron in the solution, leading to a molarity value derived from an initial preparation of 1/10 M concentration.

• A volume of 10 ml is used for dilution, resulting in a new molarity calculated as 1/5 * x .

Determining Strength of KMnO4

• Following the molarity calculation, the next step involves determining the strength of KMnO4 by multiplying its molarity with its molar mass.

• The molar mass of KMnO4 is specified as 158 g/mol, which will be used to find its strength expressed in grams per liter.

• The speaker mentions that both titration processes have been covered and offers additional resources for viva questions related to salt analysis.