A student was as ked to determine the molecular weight of a weak monoprotic dry acid (HX). She was provided the following laboratory equipment: a balance (accurate to 0.001g), distilled water, a 100.00 mL volumetric flask, a supply of sodium hydroxide solution of unknown concentration, a bottle of phenolphthalein, a 100.00 mL graduated cylinder (accurate to 0.01 mL), and a supply of oxalic dihydrate (H2C2O4. 2H2O).
a. Describe the theory of titration and how it is used.
b. Suppose the student had used 20.00 grams of the acid and dissolved the acid in distilled water to bring the volume to exactly 100.00 mL. She then added several drops of phenolphthalein to the acidic solution. She then titrated a 50.00 mL sample of this acidic solution with the sodium hydroxide solution and found that it took 42.33 mL of NaOH to reach the end point. She repeated her procedure and found that it took 42.89 mL of NaOH to reach the end point. In order to determine the molarity of the sodium hydroxide solution, she discovered that it took exactly 50.00 mL of sodium hydroxide solution to neutralize 1.500 grams of oxalic acid dihydrate.
i. Determine the molarity of the NaOH solution.
ii. Calculate the molecular weight of the unknown acid.
c. Sketch a titration curve of what the titration of the dry acid vs. sodium hydroxide might look like and explain the diagram.