Question 389Steam Plants - Assistant Engineer

The correct answer is B) the sample color changes from pink to clear. Explanation: To test the alkalinity of a boiler water sample, phenolphthalein is added initially. Phenolphthalein is a pH indicator that turns pink in alkaline solutions. The sample is then slowly titrated (added drop by drop) with an acid until the pink color disappears and the solution becomes clear. This point indicates that the alkalinity has been neutralized, and the alkalinity of the sample can be determined. The other options are incorrect because: A) the sample does not change from clear to pink, it changes from pink to clear; C) the chloride concentration is not being measured, only the alkalinity; and D) the titration is continued until the pH reaches the endpoint, not a specific pH of 10.5.