Question

Why starch is never added in beginning of titration?

Answer 1

In an iodometric titration, the roles are reversed. Starch is now used as an indicator for the presence of iodine. ... As to why it is added near the end of the titration rather than at the beginning is because the starch-iodine complex at high I2 concentrations is relatively stable.

Answer 2

Answer:

Starch is not added at the beginning of titration as we would not get a proper endpoint in during the titration.  

Explanation:

• Near the conclusion of the titration, when diluted iodine has given the solution a light yellow hue, the starch indicator is added.
• When the iodine content is high, the indicator is not added at the start of the titration for two reasons.
• First, if a significant amount of iodine were taken up by the starch, a diffuse endpoint would be produced by the gradual dissociation of the starch-iodine complex.
• Second, extremely acidic fluids are used for iodometric titrations, which encourages the interaction of oxidising agents with iodide.
• Starch tends to hydrolyze (decompose) in acidic environments, eliminating its indicator properties.

To get a proper endpoint in the titration, starch is not added at the start of a titration.

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