Question

Why could we not simply weigh out solid sodium hydroxide to make a known NaOH (aq) solution? In other words, why is the standardization process using KHP necessary? O a. NaOH (s) is hygroscopic O b. NaOH(s) can't be dissolved in water O C. Because NaOH (s) is a weak base O d. Both options (b) and (c) are correct

Answer 1

NaOH IS HYGROSCOPIC NaOH is naturally an inexpensive, highly soluble, and relatively easy to use base, so it's often the go-to chemical for simple titrations; however, it is far from perfect. First of all, solid NaOH absorbs water from the air, so accurately weighing a sample during the preparation of a solution is impossible. Secondly, a solution of NaOH tends to absorb atmospheric carbon dioxide, which is weakly acidic. Standardization is typically carried out by titrating the NaOH solution with a primary standard, an ultra-pure, easily soluble acid such as potassium hydrogen phthalate (KHP). Unlike NaOH, KHP can be used to prepare a solution whose concentration is known with a high degree of precision. The only way to accurately assess the molar concentration of a previously prepared NaOH solution, therefore, is to titrate it with a solution such as KHP. Once the NaOH solution has been standardized and its concentration is well-known, it can be used to titrate other acid solutions such as HCI.