Answer all questions in the space provided. Number each question in your response. Answer each question in no more than 100 words (words exceeding this limit will not be considered in grading). One or more of the following questions will be graded.
1. Imagine the following reaction is at equilibrium in a container with a volume of 1 L:
What happens if we decrease the volume (keeping the temperature constant) of the container?
2. You wish to titrate 25.0 mL of a 0.187 M aqueous solution of lactic acid (C3H6O3, Ka= 1.4 x 10-4) with an aqueous solution of 0.167 M KOH. (Assume only the single most acidic proton reacts). Calculate each of the following:
i) The initial pH of the lactic acid solution
ii) The pH of the solution at the equivalence point
iii) The pH after the addition of 40.5 mL of KOH solution
3. Equal numbers of moles (0.10 mol each) of HNO3, lactic acid (C3H6O3= HA), and NH3 (which has Kb = 1.7 x 10-5) are mixed in water. What are the three species in this solution (other than water) that are present in the highest concentrations?
4. While we typically use water as our solvent, it is possible to use other compounds. Liquid ammonia (NH3(l)) is one such example.
Like water, NH3 can undergo auto-dissociation:
It is known that NH2– is a stronger base than OH– and NH4+ is a weaker acid than H+.
Interestingly, while lactic acid dissolved in water has a Ka = 1.4 x 10-4, in NH3(l) lactic acid has a Ka = 10.
(i) Show the chemical reaction between lactic acid (C3H6O3) and water.
(ii) Show the chemical reaction between lactic acid and ammonia.
(iii) Propose an explanation for why lactic acid behaves as a much stronger acid in liquid ammonia.