Chemistry 102 1 REVIEW QUESTIONS Test 2 1. Calculate the pH of a 1.8 M solution of methyl amine (CH3NH2). Kb=4.38 x 10–4. 2. Calculate the pH of a solution prepared by adding 40.0 mL of 0.10M NH3 to 20.0 mL of water. (Kb of NH3 = 1.8x10–5) 3. Calculate the pH of a solution resulted from mixing 200. mL of HCl solution (pH=3.00) with 100. mL of HCl solution (pH=2.00). 4. How many grams of ammonia are needed to make 1.25 L solution with a pH of 11.68? (Kb of NH3 = 1.8x10–5)2 5. The solubility of CO2(g) in pure water is 0.0037 mol/L. Assuming that dissolved CO2 is in the form of H2CO3(aq), what is the pH of a 0.0037 M solution of dissolved CO2? (Ka1 for H2CO3 = 4.3 x 10-7) 6. Calculate the pH of a 7.5x10–6 M solution of Mg(OH)2. 7. Phenol (C6H5OH) has a Ka value of 1.6 x 10–10. What is the Kb value for phenoxide ion (C6H5O–)? 8. A benzoic acid solution (C6H5CO2H) has a pH of 2.80. Given that Ka of benzoic acid is 6.4x10–5, calculate the concentration and percent dissociation of this acid.3 9. Determine the pH of a 0.10 M NaCN solution. 10. Write net ionic equations for the reactions that take place when aqueous solutions of the following substances are mixed: a) sodium cyanide and nitric acid b) potassium hydrogen sulfate and lithium acetate 11. Based on molecular structure, choose the stronger acid in each pair. Explain your reasoning. a) H2S or H2Se b) HClO2 or HClO c) H2SO4 or H2SeO4 d) CCl3CO2H or CH3CO2H 12. For each pair given below, determine which is more basic. (Assume the same concentration for all solutions). a) Solution of NaClO and solution of HF b) Solution of KCl and solution of KClO2 c) Solution of NH4Cl and solution of HCN4 13. Calculate the pH and [CN–] in a solution that is 0.050 M HC2H3O2 and 0.050 M HCN. (Ka acetic acid = 1.8x10-5 and Ka HCN = 4.9x10-10) Note: Concentration of acids given are after mixing. 14. Complete the reaction shown below and determine whether the forward reaction or the reverse reaction is favored. HNO2 + F– 15. What is the change in pH if [H3O+] changes by each of the following factors? a) 1000 b) 1.0x105 c) 2.05 ANSWERS 1) 12.45 2) 11.04 3) 2.40 4) 27.2 g 5) 4.40 6) 9.18 7) 6.3x10–5 8) 4.1% 9) 11.15 10) No answers provided 11) a) H2Se (Se larger than S causing acid bond to be weaker) b) HClO2 (The greater number of oxygens cause more polar acidic bond) c) H2SO4 (Sulfur is more electronegative than Se causing the acid bond to be more polar) d) CCl3CO2H (the 3 electronegative chlorine atoms withdraw electrons from the oxygen, in turn causing the acidic bond to become more polar) 12) No answers given 13) pH = 3.02; [CN-] = 2.6x10–8 14) No answers provided 15) a) 3 b) 5 c)