Question:
Which of the following indicators is used for determination of saponification value of ghee?
Which of the following indicators is used for determination of saponification value of ghee?
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Phenolphthalein is the standard indicator for acid-base back-titrations of excess alkali in saponification and acid value determinations.
Updated On: Aug 5, 2026
- Starch
- Iron alum
- Methylene blue
- Phenolphthalein
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The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept:
The Saponification Value is a chemical index used to estimate the average molecular weight of fatty acids in a fat sample.
It is defined as the number of milligrams of potassium hydroxide (\(\text{KOH}\)) required to saponify one gram of fat.
The method involves refluxing the fat with an excess of alcoholic \(\text{KOH}\), followed by back-titration of the unreacted alkali against standard hydrochloric acid (\(\text{HCl}\)).
Step 2: Detailed Explanation:
Because this assay concludes with the neutralization of a strong base (\(\text{KOH}\)) with a strong acid (\(\text{HCl}\)), an acid-base indicator is required to detect the equivalence point:
Phenolphthalein is the standard indicator used for this titration.
It changes color from pink in alkaline solutions (\(\text{pH} > 0\)) to colorless in acidic solutions (\(\text{pH} < 2\)), which aligns with the titration endpoint.
Other indicators listed are used in different types of titrations:
Starch is a starch-iodine indicator used in iodometric and iodimetric titrations.
Iron alum (ferric ammonium sulfate) is an indicator used in Volhard's argentometric back-titration.
Methylene blue is a redox indicator used in oxidation-reduction titrations or specific dye-reduction tests in milk.
Step 3: Final Answer:
Therefore, phenolphthalein is the indicator used to determine the saponification value of ghee.
The Saponification Value is a chemical index used to estimate the average molecular weight of fatty acids in a fat sample.
It is defined as the number of milligrams of potassium hydroxide (\(\text{KOH}\)) required to saponify one gram of fat.
The method involves refluxing the fat with an excess of alcoholic \(\text{KOH}\), followed by back-titration of the unreacted alkali against standard hydrochloric acid (\(\text{HCl}\)).
Step 2: Detailed Explanation:
Because this assay concludes with the neutralization of a strong base (\(\text{KOH}\)) with a strong acid (\(\text{HCl}\)), an acid-base indicator is required to detect the equivalence point:
Phenolphthalein is the standard indicator used for this titration.
It changes color from pink in alkaline solutions (\(\text{pH} > 0\)) to colorless in acidic solutions (\(\text{pH} < 2\)), which aligns with the titration endpoint.
Other indicators listed are used in different types of titrations:
Starch is a starch-iodine indicator used in iodometric and iodimetric titrations.
Iron alum (ferric ammonium sulfate) is an indicator used in Volhard's argentometric back-titration.
Methylene blue is a redox indicator used in oxidation-reduction titrations or specific dye-reduction tests in milk.
Step 3: Final Answer:
Therefore, phenolphthalein is the indicator used to determine the saponification value of ghee.
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