255.在以酚酞为指示剂、用NaOH为标准滴定溶液分析酸的含量时,近终点时应避免剧烈摇动。()

(The first question): 在以酚酞为指示剂、用 NaOH 为标准滴定溶液分析酸的含量时，近终点时应避免剧烈摇动。 (A.正确 B.错误) "During the titration of an acid using phenolphthalein as an indicator and NaOH as the standard titrant, violent shaking should be avoided near the endpoint." (A. Correct) 解析 (Analysis): The answer is correct (A.正确). Phenolphthalein is an indicator that changes color at a specific pH range, indicating the endpoint of the titration. At the endpoint, the reaction between the acid and the base is nearly complete, and adding one extra drop of the titrant could cause excessive change in the solution's pH, leading to an inaccurate result. Avoiding violent shaking near the endpoint ensures a more accurate determination of the endpoint and, consequently, a more precise measurement of the acid's concentration.