Question

A student wants to investigate the amount of Ascorbic acid in orange juice, with a simple NaOH titration what other substances/compounds of the juice might interfere the results, to which extent?

Answer 1

Citric acid, malic acid, and the orange pigments in orange juice might interfere with the results.

Explanation:

There are three types of substances that might interfere with the results.

A. Other acids present in orange juice

Citric acid, malic acid, and several other acids are present in orange juice.

`"NaOH"` is a strong base.

It will react with all the acids present in orange juice.

Thus, if these other acids are present, you will use too much `"NaOH"`, and you will think that the juice contains more ascorbic acid than is really present.

B. The coloured pigments present in orange juice

Orange juice contains several orange pigments called carotenoids.

If you are doing an acid-base titration, the orange pigments will make it difficult to see the colour change of the indicator at the end-point.

You may find it difficult to get good agreement in successive titrations.

C. Suspended solids in the orange juice

Suspended solids (pulp) in the orange juice will also make it difficult to identify a colour change at the end-point.