BCIT Winter Chem Exam #2

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1 BCIT Winter 2016 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

2 Section I: Multiple choice (15 points total, 1 point each) Choose the BEST answer to the following questions. 1. In a solubility equilibrium, the a. Rate of dissolving equals the rate of crystallization b. Neither dissolving nor crystallization are occurring c. Concentration of solute and solvent are always equal d. Mass of dissolved solute is greater than the mass of solution 2. Which of the following represents the dissociation equation of a salt in water? a. KCl(s) K + (aq) + Clˉ(aq) b. Ca 2+ (aq) + SO 42ˉ(aq) CaSO 4 (s) c. HCl(aq) + KOH(aq) KCl(aq) + H 2 O() d. 2Na(s) + 2H 2 O() 2NaOH(aq) + H 2 (g) 3. There are 10.0 ml of four solutions. One solution each of 0.10 M Cl, 0.10 M Br, 0.10 M IO 3, and 0.10 M BrO 3. Equal moles of AgNO 3 are added to each of the four solutions. A precipitate forms in all but one solution. Which solution does not form a precipitate? a M Cl b M Br c M IO 3 d M BrO 3 4. Solid NaCl is added to a saturated AgCl solution. How have [Ag + ] and [Cl ] changed when equilibrium has been reestablished? [Ag + ] [Cl ] a. increased increased b. increased decreased c. decreased increased d. decreased decreased Page 2 of 7

3 5. Which of the following expressions represents [Fe 3+ ] in a saturated Fe(OH) 3 solution? a. b. c. d. 6. What happens when equal volumes of 0.20 M BaCl 2 and 0.20 M Pb(NO 3 ) 2 are mixed? a. only PbCl 2 precipitates b. only Ba(NO 3 ) 2 precipitates c. both PbCl 2 and Ba(NO 3 ) 2 precipitate d. no precipitate forms 7. Which of following 1.0 M solutions will have the greatest electrical conductivity? a. HI b. H 2 S c. HCN d. H 3 PO 4 8. The relationship a. K a for H 3 P 2 O 7ˉ b. K b for H 3 P 2 O 7ˉ c. K a for H 2 P 2 O 72ˉ d. K b for H 2 P 2 O 72ˉ is the 9. What is produced when CH 3 NH 2 acts as a base in water? a. CH 3 NH + b. CH 3 NH 3 + c. CH 3 NH 2 d. CH 3 NH Which indicator below has K a = 1.0x10 6? a. methyl red b. phenolphthalein c. bromthymol blue d. chlorophenol red Page 3 of 7

4 11. Which of the following salt solutions is neutral? a. KBr b. FeCl 3 c. Li 2 C 2 O 4 d. NaHCO Which of the following equations describes the predominant equilibrium that occurs at the equivalence point of a titration between CH 3 COOH(aq) and NaOH(aq)? a. H + (aq) + OH (aq) H 2 O() b. CH 3 COO (aq) + H 2 O() CH 3 COOH(aq) + OH (aq) c. CH 3 COOH(aq) + NaOH(aq) NaCH 3 COO(aq) + H 2 O() d. H + (aq) + CH 3 COO (aq) + Na + (aq) + OH (aq) Na + (aq) + CH 3 COO (aq) + H 2 O() 13. Consider the following equilibrium, where the concentrations are given below the species: HCN(aq) + H 2 O() H 3 O + (aq) + CN (aq) 1.0 M 2.2X10 5 M 2.2x10 5 M Why is the above solution not considered to be a true buffer solution? a. excessive [HCN] b. excessive [H 3 O + ] c. insufficient [CN ] d. insufficient [H 3 O + ] 14. What is the oxidation number of iron in magnetite, Fe 3 O 4 a. + 4 / 3 b. +2 c. + 8 / 3 d Identify the reducing agent in the following reaction: Zn + 2MnO 2 + 2H 2 O Zn(OH) 2 + 2MnO(OH) a. Zn b. MnO 2 c. H 2 O d. Zn(OH) 2 Page 4 of 7

5 Section II: Written problems (15 points total). 16. What is the maximum number of moles of Cl that can exist in ml of 2.0 M AgNO 3? (2 points) Must consider AgCl(s) Ag + (aq) + Cl (aq) K sp =[ Ag + ][ Cl ] = 1.8x10 10 where [ Ag + ] = 2.0 M from the AgNO n Cl = (9.0x10 11 M)( L) = 4.5x10 11 mol Cl 17. A mixture is prepared by adding 40.8 ml of M Mg(NO 3 ) 2 and 31.6 ml of M Sr(OH) 2. What mass in grams of Mg(OH) 2 will be formed and what will be the concentration of each of the ions after the reaction? The molar mass of Mg(OH) 2 is 58.3 g/mol. (5 points) Mg 2+ (aq) + 2OH (aq) Mg(OH) 2 (s) K sp = 5.6x10 12 = [Mg 2+ ][OH ] Mg(OH) 2 (s) Mg 2+ (aq) + 2OH (aq) I R C x 2x E x x , , Page 5 of 7

6 18. What is the ph of a 0.10 M FeCl 3 solution? When Fe 3+ is in water it forms Fe(H 2 O) (4 points) When FeCl 3 is in solution it forms Fe(H 2 O) 3+ 6 and Cl. Cl is neither and acid or base so it will not affect the ph of a solution. But Fe(H 2 O) 3+ 6 is a weak acid with K a = 6.0x10 3. Fe(H 2 O) 3+ 6 (aq) H + (aq) + Fe(H 2 O) 5 (OH) 2+ (aq) I C x x x E 0.10 x x x , Balance the following redox reaction in basic solution: (4 points) Sb 2 S 3 + NO 3ˉ NO 2 + SO 42ˉ + Sb 2 O 5 Sb 2 S H 2 O 3 SO 42ˉ + Sb 2 O H++ 28 eˉ 28(2 H++ NO 3ˉ + eˉ NO 2 + H 2 O) Sb 2 S NO 3ˉ + 22 H+ 3 SO 42ˉ + Sb 2 O NO H 2 O 22 H₂O 22 H OHˉ Sb 2 S NO 3ˉ + 11 H 2 O 3 SO 42ˉ + Sb 2 O NO OHˉ Page 6 of 7

7 Equations and Constants ph = log[h+] poh = log[ohˉ] [H+] = 10 ph [OHˉ] = 10 poh ph + poh = 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

BCIT Winter Chem Exam #2

BCIT Winter Chem Exam #2 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