Determining the pH of substances such as purple grape juice and catsup using test strips can be difficult. Why?
Explanation:
Due to the tartaric acid present in these substances, this is a weak acid and is the predominant type of acid in grapes.
pH meters for these substances, measure the total acidity of the sample and convert it into tartaric acid concentration; The test strips are a qualitative method of measurement and their result can give different opinions.
