Chemistry 102 REVIEW QUESTIONS TEST 3 1. Calculate the pH of a solution containing 0.100 M sodium formate (NaHCO2)and 0.180 M formic acid (HCHO2). (Ka formic acid = 1.8x10–4) 2. A buffer is prepared by adding 5.00 g of NH3 and 20.0 g of NH4Cl to enough water to form 2.50 L of solution. a) Calculate the pH of this buffer. b) Calculate the pH of the solution when 0.200 g of NaOH is added to 1.50 L of this buffer.Chemistry 102 3. Will Mn(OH)2 precipitate from solution if the pH of a 0.050 M solution of MnCl2 is adjusted to 8.00? (Ksp of manganese hydroxide is 1.9x10–13) 4. Calculate the [Cu2+] in 1.0 L of a solution that contains 1.0x10–3 mole of Cu(NO3)2 and that is 0.10 M in NH3. (Kf for Cu(NH3)42+ = 5.0x1012) 5. Consider the titration of 25.0 mL of 0.0800 M H2CO3 with 0.100 M KOH. Calculate the pH of the solution after (a) addition of 10.0 mL of base, and (b) at equivalence point. (Ka for carbonic acid = 4.3x10–7)Chemistry 102 6. A 0.229-g sample of an unknown monoprotic acid is titrated with 0.112 M NaOH. The resulting titration curve is shown below. Based on this information, determine the molar mass and the Ka of the acid. 7. Calculate the solubility of Au(OH)3 in 1.0 M nitric acid solution. (Ksp= 5.5x10–46) Is this value greater or less than the solubility in pure water? Explain.Chemistry 102 8. A 0.25 mol sample of a weak acid with an unknown pKa was combined with 10.0 mL of 3.00 M KOH, and the resulting solution was diluted to 1.500 L. The measured pH of the final solution was 3.85. What is the pKa of the weak acid? 9. A solution consists of 0.050 M Mg2+ and 0.020 M Cu2+. (a) Which ion will precipitate first as OH– is added to the solution? (b) What concentration of OH– is necessary to begin the precipitation of each cation? (Ksp for Mg(OH)2 = 1.8x10–11 and Ksp for Cu(OH)2 = 2.2x10–20) 10. Calculate the solubility of CuX in a solution that is 0.150 M in NaCN. (Ksp for CuX = 1.27x10–36; Kf for Cu(CN)42– = 1.0x1025)Chemistry 102 ANSWERS 1. pH = 3.48 2. a) pH = 9.15 b) pH = 9.17 3. No precipitation occurs 4. [Cu2+] = 2.4x10–12 M 5. a) pH = 6.37 b) pH = 9.50 6. molar mass = 82 g/mol Ka= 1.0x10–3 7. a) 5.5x10–4 M b) greater 8. pKa = 4.72 9. a) Cu(OH)2 will precipitate first b) [OH–] = 1.0x10–9 for Cu(OH)2 to precipitate [OH–] = 1.9x10–5 for Mg(OH)2 to precipitate 10. 8.0x10–8