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CHEMISTRY 1C

MIDTERM 2

22 MAY 2025

1. (20 POINTS TOTAL) A chemical process requires a pH of 4.50. A buffer made up of a mixture of acetic acid (CH3COOH, pKa = 4.76) and sodium acetate (NaCH3COO, 82.0 g/mol) is used to ensure that the pH of the solution does not deviate from the target pH.

(10 points) What mass of sodium acetate should you add to 200.0 mL of a 0.20 M acetic acid solution to obtain a buffer with the target pH?

(5 points) Calculate the pH of this buffer after the addition of 7.0 mmol of HCl.

(5 points) Calculate the pH of this solution if we instead add 40. mmol NaOH.

2. (20 POINTS TOTAL) Oxalic acid is the simplest dicarboxylic acid, with the formula HOOC–COOH (pKa1 = 1.25, pKa2 = 4.14)

HOOC–COOH + H2O ⇌ H3O + + HOOC–COO- pKa1 = 1.25

HOOC–COO- + H2O ⇌ H3O + + -OOC–COO- pKa2 = 4.14

(5 points) Write the equilibrium expression for the first acid ionization constant, Ka1.

(5 points) Write the equilibrium expression for the second acid ionization constant, Ka2.

(5 points) Calculate the values for Ka1 and Ka2.

Ka1 =

Ka2 =

(5 points) Calculate the pH of a 0.1 M solution of oxalic acid.

pH =

3. (20 POINTS) An electrochemical cell is prepared at 298 K using Ag(s) and Fe(s) with solutions of Ag+ and Fe3+. The half reactions are as follows with standard potentials listed.

Ag+ (aq) + e- → Ag (s) E° = 0.80 V

Fe3+ (aq) + 3e- → Fe (s) E° = -0.036 V

(5 points) Write a balanced electrochemical equation that is spontaneous.

(5 points) Write the shorthand expression for this electrochemical cell.

4. (10 POINTS TOTAL) For each species, fill in the bubbles corresponding to the correct acid/base classification(s). Hydrochloric acid, HCl, is shown as an example. All correct answers must be filled to receive credit for each species (2 points each).

6. (20 POINTS TOTAL) Consider the following equilibria:

AgI (s) + H2O (l) ⇌ Ag+ (aq) + I- (aq) Ksp = 8.5 x 10-17

Ag+ + 2CN- ⇌ Ag(CN)2 - (aq) Kf = 1.0 x 1021

(5 points) Calculate the molar solubility of AgI in pure water.

(5 points) Write the chemical equation for the solubilization of AgI (s) in a solution of CN- .

(5 points) Write the expression for the new equilibrium constant, K, for the solubilization of AgI (s) in a solution of CN- as a function of the concentrations of relevant species.

K =

(5 points) Calculate the value of K for the solubilization of AgI (s) in a solution of CN- .

K =