Question

Why do we use absorbance to monitor the reaction rate? (in an experiment with crystal violet). Is the correct answer a, b, c, or d?

a. Crystal violet is poisonous and cannot be titrated

b. Spectrophotometery is an inexpensive method

c. Crystal violet and basic phenolphthalein are colored solutions

d. All of the above

Answer 1

All of the above is true.

(a) is factually correct.

(b) is true because, in spectrophotometry, we can simply take the reaction mixture and measure absorbance at different times to monitor the reaction rate. No expensive chemicals and equipment have to be used. (Spectrophotometers are quite common these days)

(c) is true. We cannot simply use phenolphthalein as an indicator and get the endpoint because crystal violet is itself colored.