Chemistry 17 (Second Long Sample Exam) I. Modified True or False: Read the following statements carefully, and then write TRUE if the statement is true. Otherwise, change the underlined word to make the statement true. 1. Consider equal molarities of three acids, the order of increasing pH is HCl < HBr < HI. 2. Addition of KNO 3 crystals will decrease the solubility of Ag 2CrO 4. 3. Forward reaction is favored when the reaction quotient, Q, is greater than the equilibrium constant, K c. 4. The volume of 0.20 M NaOH required to titrate 30.00 mL of 0.65 M HCl to equivalence point is equal to the volume of 0.20 M NaOH required to titrate 30.00 mL of 0.65 M CH 3COOH to equivalence point. 5. If equal amounts of HNO 2 (K a = 4.5 x 10-4 ) and C6H5NH2 (K b = 4.2 x 10-10 ), the resulting solution is slightly acidic. 6. A 0.30 M Na4P2O7 has greater ionic strength than 0.70 M Pb 3(PO4 ) )2. 7. At a given temperature, the equilibrium equilibrium constant, K c, will increase when using more concentrated reagents. -11 -5 8. Precipitation of Mg(OH) 2(s) (K sp sp= 1.8 x 10 ) from 0.05 M MgCl2 and 0.15 M NH3 (K b = 1.8 x 10 ) will only occur if K sp sp is greater than Qsp. -10 9. The order of decreasing solubility in 0.100 M NH3 is AgCl > AgBr > AgI. (K sp, sp, AgCl= 1.8 x 10 , K sp, sp, AgBr= 3.3 x 10-13, K sp, sp, AgI= 1.5 x 10-16 ) 10. Ag 2CrO 4 is less soluble in an aqueous NH 3 solution than in H 2O. II. Multiple Choice: Choose the letter of the best answer. 1. The following will increase the molar solubility of Cu 3(AsO4 ) )2, except: A. Increase in the temperature of the solution C. Addition of 0.150 M Na3 AsO AsO 4 2+ B. Addition of 0.150 M NH 3 D. Using more dilute Cu solution 2. The H 3O+ produced by H 3PO4(aq) generally came from: A. Third ionization of H 3PO4 B. First ionization of H 3PO4
C. H 2O ionization D. Impurities of H 3PO4 solution
3. For a hypothetical reaction 2A(g) + 3B (g) ⇌ 4C(g) + 2D (s), the reverse reaction is favored by: A. Addition of 2 moles of B C. Increase in pressure B. Increase in temperature of the system D. Increase in volume 4. Which of the following can be used as A. Methyl orange B. Bromthymol blue C. Phenolphthalein Phenolphthalein D. Alizanin yellow-R 5. The following are acidic salts except: A. (NH 4 ) )2SO4 B. AlCl3
an indicator for a CH 3COOH-NaOH titration? pH 3(red) – pH 5(yellow) pH 6.5(red) – pH 7.5(blue) pH 8(colorless) – pH 9.5(pink) pH 10(yellow) – pH 12(violet)
C. C 5H5NHCl D. Na2CO3
III. Cause and Effect: Determine the effect (increase, decrease, no effect or indeterminate) of the parameter in column B on the given condition in column A. Condition
Parameter
1. The solvent is changed from H 2O to CH3COOH. 2. Use of more concentrated FeCl3 in the [Fe(SCN)]2+ experiment. 3. Addition of excess OH - to Zn2+ solution 4. The indicator used in the titration of weak base and strong acid changes color at the acidic range. 5. 35.0 mL of acid was added to the H 2CO3-KHCO3 buffer.
K a of HCl amount of [Fe(SCN)]2+ formed Molar solubility of Zn(OH)2 pH of endpoint pKa
IV. Problem Solving: Read each problem carefully. Show complete solutions and box your final answer. 1. Consider 200 mL of 0.20 M HCN solution. a. Find the acid dissociation constant, Ka, of HCN at 298 K given that the standard enthalpy of solution is 84 kJ/mol and standard entropy change is 0.106 kJ/mol K. b. How many milliliters of 0.35 M NaOH solution should be added to the solution to increase its pH by 3? ·
2. 50 mL of 0.90 M citric acid, C3H5O(COOH)3, with three ionizable protons is titrated with 0.30 M NaOH. -3 C3H5O(COOH)3 ⇌ H+ + C 4H5O3(COOH)2K a1 a1 = 7.4 x 10 -5 C4H5O3(COOH)2- ⇌ H+ + C5H5O5COOH2K a2 a2 = 1.7 x 10 C5H5O5COOH2- ⇌ H+ + C 6H5O7 3K a3 a3 = 7.4 x 10 -7 Determine the pH of the solution when: a. 0.00 mL of NaOH is added. b. 100.00 mL of NaOH is added. c. 150.00 mL of NaOH is added. d. 300.00 mL of NaOH is added. 3. What is the molar solubility of AgI(K sp, sp, AgI= 1.5 x 10-16 ) in 0.200 M Na 2S2O3?(Ag+ complexes with S 2O32-(aq) to form [Ag(S 2O3 )2 ] ]3-, with K f f = 2.0 x 10-13 ).
