BCIT Winter 2015 Chem 0012 Exam #2 Name: Attempt all questions in this exam. Read each question carefully and give a complete answer in the space provided. Part marks given for wrong answers with partially correct reasoning/calculations. Constants and equations are attached at the back. Data sheets and tables are provided. Total points = 30 Page 1 of 7
Section I: Multiple choice (15 points total, 1 point each) Choose the BEST answer to the following questions. 1. The solubility of a solute is best determined from which type of solution? a. a saturated solution b. any solution at 25 C c. an unsaturated solution d. a supersaturated solution 2. Which equation represents the reaction between 0.2 M Na 2 CO 3 and 0.2 M Ba(NO 3 ) 2? a. Na + (aq) + NO 3 (aq) NaNO 3 (s) b. Ba 2+ (aq) + CO 3 ² (aq) BaCO 3 (s) c. Na 2 CO 3 (s) 2Na + (aq) + CO 3 ² (aq) d. Ba(NO 3 ) 2 (s) Ba² + (aq) + 2NO 3 (aq) 3. Which compound will have the lowest molar solubility? a. BeS b. FeS c. ZnS d. Cs 2 S 4. Which relationship can be used to calculate the maximum [Ba 2+ ] that can exist in a solution of Ba 3 (PO 4 ) 2? a. b. c. d. 5. What is the maximum [Pb 2+ ] possible in a 0.10 M NaCl solution? a. 1.2x10 5 M b. 6.0x10 5 M c. 1.2x10 3 M d. 3.0x10 3 M Page 2 of 7
6. What is the conjugate acid of the base HAsO 4 ²? a. AsO 4 ³ b. H 2 AsO 4 ² c. H 2 AsO 4 d. H 3 AsO 4 7. The following equilibrium favours the formation of products: NH 2 OH + CH 3 NH 3 + CH 3 NH 2 + NH 3 OH + Which is the strongest acid? a. NH 3 OH + b. NH 2 OH c. CH 3 NH 2 + d. CH 3 NH 3 8. The S² ion is a base with a K b value of 0.77. What is the K a value for HS? a. 1.3x10 14 b. 9.1x10 8 c. 1.1x10 7 d. 7.7x10 13 9. Which equation best describes the interaction of a weak base with water? a. NaOH(aq) Na + (aq) + OH (aq) b. CH 3 CH 2 OH () CH 3 CH 2 OH(aq) c. H 2 PO 4 ² (aq) + H 2 O() PO 4 ³ (aq) + H 3 O + (aq) d. N 2 H 4 (aq) + H 2 O() N 2 H 5 + (aq) + OH (aq) 10. What is the K a expression for H 3 PO 4? a. b. c. d. Page 3 of 7
11. What is the predominant net ionic equation for the hydrolysis of (NH 4 ) 2 HPO 4? a. NH + 4 (aq) + H 2 O() H 3 O + (aq) + NH 3 (aq) b. HPO 4 ² (aq) + H 2 O() H 3 O + (aq) + PO 3 4 (aq) c. (NH 4 ) 2 HPO 4 (aq) + H 2 O() 2NH + 4 (aq) + HPO 4 ² (aq) d. HPO 4 ² (aq) + H 2 O() OH (aq) + H 2 PO 4 (aq) 12. Which of the following salt solutions is acidic? a. KBr b. FeCl 3 c. Li 2 C 2 O 4 d. NaHCO 3 13. Which of the following could typically be used to prepare a buffer solution? a. NaHC 2 O 4 and Na 2 C 2 O 4 b. Na 2 C 2 O 4 and NaOH c. HNO 3 and NaNO 3 d. HNO 3 and NaOH 14. What is the oxidation number of O in Na 2 O 2? a. 2 b. 1 c. +1 d. +2 15. Consider the following reaction: Co + SO 4 ² + 4H + Co 2+ + H 2 SO 3 + H 2 O Which statement is correct? a. The sulphur is oxidzed and the cobalt is reduced. b. The cobalt is oxidzed and the sulfur is reduced. c. The cobalt is oxidzed and the hydrogen is reduced. d. The oxygen is oxidzed and the hydrogen is reduced. Page 4 of 7
Section II: Written problems (15 points total). 16. The solubility of Zn(OH) 2 in pure water is 4.2x10 6 M. What is the value of K sp for Zn(OH) 2? (3 points) Zn(OH) 2 (s) Zn 2+ (aq) + 2 OH (aq) [Zn 2+ ] = 4.2x10 6 M [OH ] = 2(4.2x10 6 M) = 8.4x10 6 M K sp = [Zn 2+ ][OH ] 2 = (4.2x10 6 )(8.4x10 6 ) 2 = 3.0x10 16 17. a. Write the net ionic equation for the reaction between aqueous Pb(NO 3 ) 2 and aqueous NaCl. (1 point) Pb 2+ (aq) + 2Cl (aq) PbCl 2 (s) b. Show with calculations whether a precipitate will form when 15.0 ml of 0.050 M Pb(NO 3 ) 2 is added to 35.0 ml of 0.085 M NaCl. (4 points) K sp = [Pb 2+ ][Cl ] 2 = 1.2x10 5 15.0 0.050 15.0 35.0 0.0150 35.0 0.085 15.0 35.0 0.0595 Q = [Pb 2+ ][Cl ] 2 = (0.015)(0.0595) 2 = 5.3x10 5 > K sp Therefore a precipitate will form Page 5 of 7
18. What is the ph of a 0.50 M HF solution? (4 points) HF(aq) H + (aq) + F (aq) I 0.50 0 0 C -x x x E 0.50 - x x x 3.510 0.50 0.50 3.510 0.5 0.50 0.50 3.510 0.50 1.310,, 0 1.310 1.88 19. Balance the following redox reaction in acidic solution: (3 points) Sb + NO 3ˉ Sb 2 O 5 + NO 3(5 H 2 O + 2 Sb Sb 2 O 5 + 10 H+ + 10 eˉ) 10(4 H++ NO₃ˉ + 3 eˉ NO + 2 H 2 O) 6 Sb + 10 NO 3ˉ + 10 H+ 3 Sb 2 O 5 + 10 NO +5 H₂O Page 6 of 7
Equations and Constants ph = log[h+] poh = log[ohˉ] [H+] = 10 ph [OHˉ] = 10 poh ph + poh = 14.00 at 25 C K w = 1.0x10 14 at 25 C K w = K a K b px = log(x) X = 10 px A ph pk a log HA The solution to the quadratic equation ax² + bx +c =0 is 4 2 Page 7 of 7