Question

Back‐titration method is used for
A. Volatile substances 
B. Insoluble substances 
C. Substances for which a quantitative reaction proceeds rapidly only in the presence of excess of the reagent 
D. Substances that require heating with a volumetric reagent during the determination, in which decomposition or loss of the reactants would occur in the process 
Choose the correct answer from the options given below:

• A. A only
• B. A and C
• C. A, B and D
• D. A, B, C and D

Answer 1

The Correct Option is D

The question concerns the suitability of using the back-titration method for various types of substances. Let's examine each option to understand why all are correct for back-titration and justify the correct answer, which is A, B, C, and D.

1. Volatile Substances (Option A):
   • For volatile substances, direct titration may not be feasible because the substance can evaporate during the process, leading to inaccurate results. Back-titration is suitable as it involves an excess of a reagent which is then titrated, thus minimizing the loss due to volatility.
2. Insoluble Substances (Option B):
   • When dealing with insoluble substances, direct titration is ineffective since they do not dissolve completely to react with the titrant. Back-titration allows these substances to react with an excess reagent that can then be titrated, ensuring accurate measurement.
3. Substances for Rapid Reaction Only in Excess Reagent (Option C):
   • Certain substances may not react completely or quickly with the titrant unless in an excess quantity. Back-titration allows the use of excess reagent, confirming that the reaction proceeds to completion before titration.
4. Substances Requiring Heating With Reagent (Option D):
   • Some substances need heating, which could cause decomposition or loss during determination. Back-titration ensures the reaction occurs under controlled conditions, reducing the chance of these issues.

Thus, all options A, B, C, and D are correctly addressed by the back-titration method, making this the correct choice.