Question

According to Mohr method, the silver nitrate solution can be standardized against primary‐ standard grade:

• A. Sodium carbonate
• B. Sodium chloride
• C. Sodium hydrogen carbonate
• D. Sodium metabisulfite

Answer 1

The Correct Option is B

The Mohr method is a well-known technique in analytical chemistry used for the determination of chloride ion concentration in a solution by titration with silver nitrate (\( \text{AgNO}_3 \)). In this method, a primary standard is required to standardize the silver nitrate solution.

The Mohr method relies on the titration of chlorides with a silver nitrate solution in the presence of an indicator, usually potassium chromate (\( \text{K}_2\text{CrO}_4 \)). When all the chloride ions have reacted with silver ions to form the precipitate silver chloride (\( \text{AgCl} \)), the further addition of silver nitrate will react with the indicator to form a red-brown silver chromate (\( \text{Ag}_2\text{CrO}_4 \)), marking the end point of the titration.

Let's analyze the given options for the appropriate primary standard for this purpose:

• Sodium carbonate (Na₂CO₃): While sodium carbonate is a good primary standard for acid-base titrations, it is not suitable for standardizing silver nitrate in the Mohr method.
• Sodium chloride (NaCl): It is a highly stable, pure, and widely available salt that dissociates completely in solution to provide chloride ions. Thus, it is ideal for standardizing solutions like silver nitrate in the Mohr method, making it the correct choice.
• Sodium hydrogen carbonate (NaHCO₃): Similar to sodium carbonate, it is mostly used in acid-base titrations and is not suitable for chloride ion determination.
• Sodium metabisulfite (Na₂S₂O₅): This compound is commonly used as a reducing agent and is not suitable for standardizing silver nitrate.

Therefore, based on the requirements of the Mohr method, Sodium chloride (NaCl) is the correct primary standard used to standardize the silver nitrate solution. It provides the chloride ions necessary for the reaction and is available in a pure, stable form, making it suitable for accurate standardization.