Part A -

Question 1: What is the pH of 0.00112 mol/L HCl(aq) at 25^oC? Give your answer accurate to two decimal places.

Question 2: What is the pH of 5.37E-5 mol/L LiOH(aq) at 25^oC? Give your answer accurate to two decimal places.

Question 3: What is the percent ionization of HA in 0.135 mol/L HA(aq) if HA is a weak acid with pK_a = 4.75. Enter your answer accurate to three significant figures. Do not include the percent sign as part of your answer!

Question 4: Benzoic acid, HC₇H₅O₂, is a weak monoprotic acid (pKa = 4.2 at 25^oC). What is the pH of 0.135 mol/L HC₇H₅O₂(aq) at 25^oC? Give your answer accurate to two decimal places.

Question 5: Diethylamine, (C₂H₅)2NH, is a weak base (pK_b = 3.16 at 25^oC). What is the pH of 0.133 mol/L (C₂H₅)₂NH(aq) at 25^oC? Give your answer accurate to two decimal places.

Question 6: Which of the following oxo acids is the weakest acid?

(a) HIO₃

(b) HIO₂

(c) HCIO₂

(d) HBrO₃

(e) HBrO₂

(f) HClO₃

Question 7: Which of the following substances is the weakest acid in water?

(a) HF

(b) HBr

(c) HI

(d) HCl

Question 8: Oxalic acid, H₂C₂O₄, is a weak diprotic acid (pK_a,1 = 1.27 and pK_a,2 = 4.28 at 25^oC). What is the pH of 0.157 mol/L H₂C₂O₄(aq) at 25^oC? Give your answer accurate to two decimal places.

Question 9: Which of the following expressions hold for 0.10 mol/L H₃A(aq).  Assume that H₃A is a weak triprotic acid.

(a) [H⁺] = [H₂A^-] + [HA^2-] + [A^3-] + [OH^-]

(b) [H⁺][OH^-] = K_w

(c) 0.10 = [H₃A] + [H₂A^-] + [HA^2-]+[A^3-]

(d) [H₂A^-] = 2 [HA^2-] = 3 [A^3-]

(e) K_a2 = [A^3-][H⁺]/[HA^2-]

(f) K_a1K_a2K_a3 = K_w

Part B -

Question 1: What is the pH of 0.00133 mol/L H₂SO₄(aq) at 25^oC? For H₂SO⁴, K_a1 is very large and pK_a,2 = 1.96 at 25^oC. Give your answer accurate to two decimal places.

Question 2: What is the pH of a 0.153 mol/L solution of sodium benzoate, NaC₇H₅O₂, at 25^oC? (pK_a = 4.21 at 25^oC for HC₇H₅O₂.) Give your answer accurate to two decimal places.

Question 3: How many moles of NaOH must be added to 0.250 L of 0.185 mol/L HN₃(aq) to obtain a solution with pH = 5.0? Assume the temperature is 25^oC. (For HN₃, pKa = 4.72 at 25^oC). Give your answer accurate to three significant figures. You may enter 1.23x10^-3 as 1.23e^-3.

Question 4: What is the final pH of the solution when 30.0 mL of 0.137 mol/L NaOH(aq) and 50.0 mL of 0.183 mol/L HCOOH(aq) are mixed? Assume the temperature is 25^oC. (For HCOOH, pK_a = 3.74 at 25^oC). Give your answer accurate to two decimal places.

Question 5: What is the pH at the equivalence point when when 35.0 mL of 0.187 mol/L HF(aq) is titrated with 0.137 mol/L NaOH(aq)? Assume the temperature is 25^oC. (For HF, pK_a = 3.18 at 25^oC). Give your answer accurate to two decimal places.

Question 6: What is the final pH at 25^oC when 67.0 mL of 0.119 mol/L NaOH(aq) and 35.0 mL of 0.195 mol/L HA(aq) are mixed.  Assume that HA is a weak monoprotic acid with pK_a = 4.73 at 25^oC. Give your answer accurate to two decimal places.

Question 7: If 47.0 mL of 0.137 mol/L NaOH(aq) and 30.0 mL of 0.193 mol/L HA(aq) are mixed, then what is [HA] at equilibrium? Assume that HA is a weak monoprotic acid with pKa = 6.23 at 25^oC. Give your answer with three significant figures.

Question 8: Consider the following titration curve for the titration of a weak monoprotic acid, HA, with NaOH(aq). At which point(s) does the condition [A^-]_eq = [H⁺]_eq hold true? In this problem, assume that "=" means "is approximately equal to". You may make more than one selection.

(a) before the titration starts (A)

(b) at all points before the equivalence point (B)

(c) at the equivalence point (C)

(d) beyond the equivalence point (D)

(e) the condition is never satisfied