1. What is the pH after two solutions are mixed: 1. A 0.155 M H2SO4 solution with a volume of 35.0 mL and 2. A 0.225 M solution of KOH with a volume of 35.0 mL. The volumes are additive.
1. What is the pH after two solutions are mixed: 1. A 0.155 M H2SO4 solution with a volume of 35.0 mL and 2. A 0.225 M solution of KOH with a volume of 35.0 mL. The volumes are additive.
2. What is the pH of a 0.225 M solution of CH3NH2 (aq), for which Kb = 4.4 X 10-4 .
3. A buffer is prepared from 550 mL 0.250 M CH3COOH and 1.25 g NaOH (s). What is the pH of the buffer? Assume the volume does not change when the solid is added.
4. 40.0 ml of an acetic acid of unknown concentration is titrated with 0.100 M NaOH. After 20.0 mL of the base solution has been added, the pH in the titration flask is 5.10. What was the concentration of the original acetic acid solution? Ka = 1.8 X 10-5
5. Your task is to prepare a buffer solution of 1.00 L of 0.250 M acetic acid and solid sodium hydroxide. Start by writing the equation for the reaction that will form the buffer (hint: you must have both acetic acid and acetate ion in the solution; where will the acetate ion come from? Neglecting the volume change on addition of NaOH (MM 40.0 g/mol), what mass is required to produce a buffer of pH 3.75? What pH will the buffer show after the addition of 250.0 mg of solid KOH (MM 56.1 g/mol) ? Assume no volume change on addition of the base. The Ka for acetic acid is 1.8 X 10-5 .
6. A solution of an unknown acid is prepared by dissolving 0.250 g of the unknown in water to produce a total volume of 100.0 mL. Half of this solution is titrated to a phenolphthalein endpoint, requiring 12.2 mL of 0.0988 M KOH solution. The titrated solution is re-combined with the other half of the un-titrated acid and the pH of the resulting solution is measured to be 4.02. What is are the Ka value for the acid and the molar mass of the acid?
7. The indicator propyl red has a Ka of 3.3 X 10-6 . It is red at low pH and yellow at higher pH. What is the approximate pH range over which it changes color? What color would you expect it to show at a pH of 3.0? Show a calculation!
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