BCIT Winter Chem Exam #2

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1 BCIT Winter 2017 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. Which of the following is commonly used to describe the solubility of a solute? a. mass of solute/moles of solute b. moles of solution/mass of solute c. mass of solute/volume of solution d. mass of solution/volume of solute 2. What is the concentration of OH - ions in 250 ml of 0.20 M Sr(OH) 2? a M b M c M d M 3. Which of the following substances has the lowest solubility? a. BaS b. CuS c. FeS d. ZnS 4. Given a saturated solution of Ca(OH) 2 which of the following statements is always true? a. The [Ca 2+ ] is twice that of the [OH ]. b. The OH precipitates half as fast as the Ca 2+. c. The rate of crystallization equals the rate of dissolving. d. The rate of dissolving is greater than the rate of crystallization. 5. What is the K sp expression for the precipitate formed when solutions of Fe(NO 3) 3 and Sr(OH) 2 are mixed? a. K sp = [Sr 2+ ] [OH ] 2 b. K sp = [Fe 3+ ][NO 3 ]³ c. K sp = [Sr 2+ ] [NO 3 ] 2 d. K sp = [Fe 3+ ] [OH ] 3 Page 2 of 7

3 6. Which of the ions below could be used in a precipitation reaction to determine the [SO 4² ] in a water sample? a. H + b. Cs + c. Sr 2+ d. NH Consider the following equilibrium: 2H 2O( ) H 3O + (aq) + OH (aq) What changes occur to [H 3O + ] and ph when NaOH is added? [H 3O + ] ph a. increased increased b. increased decreased c. decreased increased d. decreased decreased 8. The ionization of water in endothermic. How is K w related to the temperature of water? a. K w increases as temperature increases b. K w decreases as temperature increases c. K w increases as temperature decreases d. K w remains constant as temperature changes 9. A 25.0 ml sample of H 2SO 4(aq) is titrated with 15.5 ml of 0.50 M NaOH. What is the concentration of H 2SO 4(aq)? a M b M c M d M 10. What is the complete ionic equation for the neutralization of 0.10 M Sr(OH) 2 with 0.10 M H 2SO 4(aq)? a. H + (aq) + OH (aq) H 2O( ) b. Sr 2+ (aq) + SO 42 (aq) SrSO 4(s) c. Sr 2+ (aq) + 2OH (aq) + 2H + (aq) + SO 42 (aq) SrSO 4(s) + 2 H 2O( ) d. Sr 2+ (aq) + 2OH (aq) + 2H + (aq) + SO 42 (aq) Sr 2+ (aq) + SO 42 (aq) + 2H 2O( ) Page 3 of 7

4 11. Water will act as an acid with which of the following? I. H 2CO 3 II. III. HCO 3 CO 32 a. I only b. III only c. I and II only d. II and III only 12. What is the ph of the solution formed when moles of NaOH is added to 1.00 L of M HCl? a b c d What is the conjugate base of the acid HC 4H 4O 4? a. H2C4H4O4 b. H2C4H4O4 c. C4H4O4² d. C4H4O4 14. Which solution will have the greatest electrical conductivity? a M KCl b M RbOH c M K 3PO 4 d. 2.0 M C 6H 12O When solutions containing HC 2O 4 and HSO 3 are mixed, what is predominant equilibrium reaction? a. HC 2O 4 (aq) + HSO 3 (aq) C 2O 4² (aq) + H 2SO 3(aq) b. HC 2O 4 (aq) + HSO 3 (aq) H 2C 2O 4(aq) + SO 3² (aq) c. H 2C 2O 4(aq) + HSO 3 (aq) HC 2O 4 (aq) + H 2SO 3(aq) d. HC 2O 4 (aq) + H 2SO 3(aq) H 2C 2O 4(aq) + HSO 3 aq) Page 4 of 7

5 Section II: Written problems (15 points total). 16. a) What is the molar solubility of Pb(IO 3) 2 in pure water at 25 C? (3 points) Pb(IO 3) 2(s) Pb² + (aq) + 2IO 3 (aq) K sp =[ Pb² + ][ IO 3 ]² = 3.7x10-13 let s = molar solublity of Pb(IO 3) 2 then [Pb² + ] = s and [IO 3 ] = 2s K sp =[ Pb² + ][ IO 3 ]² = (s) (2s)² = 3.7x ss = 3.7xx = 4.5xx10 5 MM b) What is molar solubility of Pb(IO 3) 2 in a M KIO 3 solution at 25 C? (3 points) The M KIO 3 solution will give an initial [IO 3 ] = M Pb(IO 3) 2(s) Pb² + (aq) + 2IO 3 (aq) I C s 2s E s s K sp =[ Pb² + ][ IO 3 ]² = 3.7x10-13 = (s) ( s)² (s) (0.020)², assume 2s << ss = 3.7xx10 13 (0.020) 2 = 9.3xx10 10 MM so assumption is OK and solubility is 9.3x10-10 M 17. a) Write the net ionic equation for the reaction between aqueous Pb(NO 3) 2 and aqueous CaBr 2. (1 point) Pb 2+ (aq) + 2Br (aq) PbBr 2(s) b) Show with calculations whether a precipitate will form when 15.0 ml of M Pb(NO 3) 2 is added to 35.0 ml of M CaBr 2. (3 points) K sp = [Pb 2+ ][Br - ] 2 = 6.6x10-6 [PPPP 2+ ] = [BBBB ] = (15.0 mmmm)(0.020 MM) 15.0 mmmm mmmm = MM PPPP2+ 2 mmmmmm BBBB (35.0 mmmm)(0.030 MM CCCCBBBB 2 ) mmmmmm CCCCBBBB 2 = MM CCCC 15.0 mmmm mmmm Q = [Pb 2+ ][Br - ] 2 = (6.0x10-3 )(4.2x10-2 ) 2 = 1.1x10-5 > K sp Therefore a precipitate will form Page 5 of 7

6 18. Calculate the ph of 0.50 M NH 3 at 25 C. Start by writing the equation for the predominant equilibrium reaction. (5 points) NH 3(aq) + H 2O(l) NH 4+ (aq) + OH (aq) I C -x x x E 0.50-x x x KK bb = KK ww KK aa = 1.0xx xx10 10 = 1.8xx10 5 = Note since x = [OH ] x > 0 xx xx xx xx = (0.50)(1.8xx10 5 ) = 3.0xx10 3 MM = [OOOO ] aaaaaaaaaaaaaaaaaaaa iiii OOOO poh = -log(3.0x10-3 ) = 2.52 ph = poh = Page 6 of 7

7 Equations and Constants ph = -log[h+] poh = -log[oh ] [H+] = 10 -ph [OH ] = 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 ph = pk + a log [ A ] [ HA] The solution to the quadratic equation ax² + bx + c =0 is xx = bb ± bb2 4aaaa 2aa 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