Question

Mono sodium salt of oxalic acid is titrated with NaOH Solution : In the second titration it is titrated with K M n O 4

Answer 1

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Answer 2

The problem describes two distinct titrations involving the monosodium salt of oxalic acid, NaHC₂O₄.

1. Titration with NaOH Solution

Type of Titration: Acid-Base Titration

Nature of Reactants:

• Mono sodium salt of oxalic acid (NaHC₂O₄): This is an acidic salt. The hydrogen oxalate ion (HC₂O₄⁻) retains one acidic proton (-COOH group) which can be donated.
• NaOH: A strong base.

Reaction: The acidic proton of NaHC₂O₄ reacts with the hydroxide ions from NaOH, leading to a neutralization reaction.

$\text{NaHC}_2\text{O}_4(\text{aq}) + \text{NaOH}(\text{aq}) \longrightarrow \text{Na}_2\text{C}_2\text{O}_4(\text{aq}) + \text{H}_2\text{O}(\text{l})$

Ionic Reaction: $\text{HC}_2\text{O}_4^-(\text{aq}) + \text{OH}^-(\text{aq}) \longrightarrow \text{C}_2\text{O}_4^{2-}(\text{aq}) + \text{H}_2\text{O}(\text{l})$

Purpose: This titration is used to determine the concentration or amount of the acidic proton present in the monosodium oxalate sample. It quantifies the acidic nature of the salt.

Indicator: Phenolphthalein is commonly used as an indicator for this titration, as the equivalence point typically lies in the basic pH range.

2. Titration with KMnO₄ Solution

Type of Titration: Redox (Reduction-Oxidation) Titration

Nature of Reactants:

• Mono sodium salt of oxalic acid (NaHC₂O₄): The oxalate ion (C₂O₄²⁻) part is a reducing agent. Carbon in the oxalate ion has an oxidation state of +3, which can be oxidized to +4 (in CO₂).
• KMnO₄: Potassium permanganate is a strong oxidizing agent.

Medium and Conditions:

• The titration is carried out in an acidic medium, typically by adding dilute sulfuric acid (H₂SO₄). This is because KMnO₄ is reduced to Mn²⁺ in acidic conditions (MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O), which is the most efficient reduction pathway.
• The reaction is often performed at an elevated temperature (around 60-70°C) to increase the reaction rate, especially in the initial stages. Mn²⁺ formed during the reaction acts as an autocatalyst.

Redox Reactions:

Oxidation Half-Reaction (Oxidation of oxalate): $\text{C}_2\text{O}_4^{2-}(\text{aq}) \longrightarrow 2\text{CO}_2(\text{g}) + 2\text{e}^-$ (Each carbon atom changes oxidation state from +3 to +4, losing 1 electron. Since there are two carbon atoms, 2 electrons are lost per oxalate ion.)

Reduction Half-Reaction (Reduction of permanganate): $\text{MnO}_4^-(\text{aq}) + 8\text{H}^+(\text{aq}) + 5\text{e}^- \longrightarrow \text{Mn}^{2+}(\text{aq}) + 4\text{H}_2\text{O}(\text{l})$

Overall Balanced Redox Reaction: To balance the electrons, multiply the oxidation half-reaction by 5 and the reduction half-reaction by 2: $5\text{C}_2\text{O}_4^{2-}(\text{aq}) \longrightarrow 10\text{CO}_2(\text{g}) + 10\text{e}^-$ $2\text{MnO}_4^-(\text{aq}) + 16\text{H}^+(\text{aq}) + 10\text{e}^- \longrightarrow 2\text{Mn}^{2+}(\text{aq}) + 8\text{H}_2\text{O}(\text{l})$

Adding the two half-reactions: $5\text{C}_2\text{O}_4^{2-}(\text{aq}) + 2\text{MnO}_4^-(\text{aq}) + 16\text{H}^+(\text{aq}) \longrightarrow 10\text{CO}_2(\text{g}) + 2\text{Mn}^{2+}(\text{aq}) + 8\text{H}_2\text{O}(\text{l})$

Considering NaHC₂O₄, the hydrogen oxalate ion (HC₂O₄⁻) also gets oxidized. The overall stoichiometry is 5 moles of HC₂O₄⁻ reacting with 2 moles of MnO₄⁻, requiring 11 H⁺ ions from the acid (5HC₂O₄⁻ + 2MnO₄⁻ + 11H⁺ → 10CO₂ + 2Mn²⁺ + 8H₂O).

Purpose: This titration is used to determine the concentration or amount of the reducing oxalate part present in the monosodium oxalate sample.

Self-Indicator: Potassium permanganate acts as its own indicator. The solution remains colorless (due to the formation of colorless Mn²⁺ ions) until the equivalence point. A single drop of excess KMnO₄ solution imparts a permanent light pink color to the solution, indicating the endpoint.

The problem describes two separate titrations of monosodium oxalate (NaHC₂O₄).

1. Titration with NaOH: This is an acid-base titration. NaHC₂O₄ is an acidic salt due to the presence of an ionizable proton in the -COOH group of the hydrogen oxalate ion (HC₂O₄⁻). It reacts with the strong base NaOH: $\text{NaHC}_2\text{O}_4(\text{aq}) + \text{NaOH}(\text{aq}) \longrightarrow \text{Na}_2\text{C}_2\text{O}_4(\text{aq}) + \text{H}_2\text{O}(\text{l})$ This titration quantifies the acidic nature of the salt.

2. Titration with KMnO₄: This is a redox titration. The oxalate ion (C₂O₄²⁻) in NaHC₂O₄ acts as a reducing agent, where carbon (oxidation state +3) is oxidized to CO₂ (oxidation state +4). KMnO₄ acts as a strong oxidizing agent, where Mn (oxidation state +7) is reduced to Mn²⁺ (oxidation state +2) in acidic medium. The balanced net ionic reaction is: $5\text{C}_2\text{O}_4^{2-}(\text{aq}) + 2\text{MnO}_4^-(\text{aq}) + 16\text{H}^+(\text{aq}) \longrightarrow 10\text{CO}_2(\text{g}) + 2\text{Mn}^{2+}(\text{aq}) + 8\text{H}_2\text{O}(\text{l})$ This titration quantifies the reducing nature of the oxalate part of the salt. KMnO₄ is a self-indicator.