University of Texas, Rio Grande ValleyCHEM 1111 A

University of Texas, Rio Grande ValleyCHEM 1111

A. Standardization of a Sodium Hydroxide Solution

Calculate the approximate mass of NaOH required to prepare 500 mL of a 0.15 M NaOH solution (Part A.2).

Calculate the approximate mass of KH₈H₄O₄ for the standardization of the NaOH solution (Part A.3).

B. Molar Concentration of an Acid Solution Acid type, HA or H2A:

Part A. The mass of KHC8H4O4 is measured to the nearest milligram; however, the volume of water in which it is dissolved is never of concern—water is even added to the wall of the Erlenmeyer flask during the titration. Explain why water added to the KHC8H4O4 has no effect on the data, whereas water added to the NaOH solution may drastically affect the data.

Part B.2. The wall of the Erlenmeyer flask is occasionally rinsed with water from the wash bottle (see Part A.6) during the analysis of the acid solution. Will this technique result in the molar concentration of the acid solution being reported as too high, too low, or unaffected? Explain.

Parts A.6 and B.2. For the standardization of the NaOH solution in Part A.6, the endpoint was consistently reproduced to a faint pink color. However, the endpoint for the titration of the acid solution in Part B.2 was consistently reproduced to a dark pink color. Will the reported molar concentration of the acid solution be too high, too low, or unaffected by the differences in the colors of the endpoints. Explain.