The equivalent weight of Na₂S₂O₃ as reductant in the reaction, Na₂S₂O₃ + H₂O + Cl₂ → Na₂SO₄ + 2HCl + S is:

• A. M/1
• B. M/2
• C. M/6
• D. M/8

The equivalent weight of a substance in a redox reaction is calculated based on the number of electrons transferred during the reaction. For sodium thiosulfate (Na₂S₂O₃) acting as a reductant, we need to determine how many moles of electrons it donates in the given reaction.

Understanding the Reaction

In the reaction:

• Na₂S₂O₃ + H₂O + Cl₂ → Na₂SO₄ + 2HCl + S

Sodium thiosulfate is oxidized to sodium sulfate (Na₂SO₄) and elemental sulfur (S). Each molecule of Na₂S₂O₃ donates 2 electrons during this process.

Calculating Equivalent Weight

The equivalent weight can be calculated using the formula:

Equivalent Weight = Molar Mass / n

Where:

• Molar Mass of Na₂S₂O₃ is approximately 158 g/mol.
• n is the number of electrons transferred (which is 2 in this case).

Final Calculation

Using the formula:

Equivalent Weight = 158 g/mol / 2 = 79 g/equiv

To express this in terms of M (molar mass), we can say:

Equivalent Weight = M/2

Correct Answer

Thus, the equivalent weight of Na₂S₂O₃ as a reductant in this reaction is B. M/2.