Question

4. Explain why the solution being titrated first turns pink then goes colorless before the endpoint is reached. 5. A student gets a dark pink color for trial 2 but uses that data to calculate the mass percent of acetic acid. Would the mass percent be too high or too low? Explain and be specific Experiment 10 Determination of the Molar Gas Constant, R

Answer 1

4. ANS: while doing the titration, usually bases are added to the acids. the indicator used is the phenolphthalein. this shows pink color in basic solution and colorless in acid solution. before endpoint, if one drop of the base is added to the acid, some part of the solution turns into pink. the reason for this is, the base consumed by that small part is little excess, which makes that small part of the solution alkaline, and consequently pink color. but when the solution is mixed properly, the color vanishes. because the overall solution turns again acidic.

5. after titration, the solution turns into dark pink. that means a little excess base is added to the solution. if the student calculates the mass of acid by that value, he will get high-value compared to the actual value present to the solution. because they follow V₁S₁=V₂S₂ relation.