CHEM 1120 test 1 - Spring 2006Page 1Circle the correct answer on the answer sheet. Use the equilibrium constants on the sheetattached.1. Calculate the pH of a 0.045 M solution of HNO3.a. 13.70 b. 12.40 c. 7.00 d. 1.35 e. 1.00()( )+3pH log H OpH log 0.045pH 1.35= −= −=CHEM 1120 test 1 - Spring 2006Page 22. Calculate the pH of a 0.050 M solution of LiOH.a. 1.00 b. 1.60 c. 7.00 d. 12.70 e. 13.70()( )- pOH log OHpOH log 0.050pOH 1.30pH 14.00 pOHpH 12.70= −= −== −=CHEM 1120 test 1 - Spring 2006Page 33. Calculate the pH of a 0.025 M solution of NaClO4.a. 1.00 b. 1.60 c. 7.00 d. 12.40 e. 13.70Na+ is the cation of a strong baseClO4– is the anion of a strong acidboth are therefore spectator ions and the solution is neutralCHEM 1120 test 1 - Spring 2006Page 44. Calculate the pH of a 2.0 M solution of HFa. 0.30 b. 0.70 c. 1.05 d. 1.45 e. 11.95HF is a weak acid. From the table Ka = 6.3 × 10–4HF + H2O º F– + H3O+[HF] [F–] [H3O+]before 2.0 0 0at equilibrium 2.0 – x x x[ ]- +3242F H OHF6.3 102.03.55 10pH 1.45aKxxx−−      =× =−= ×=CHEM 1120 test 1 - Spring 2006Page 55. Calculate the pH of a 1.0 M solution of H2NNH2.a. 12.49 b. 11.04 c. 7.00 d. 2.96 e. 1.51H2NNH2 is a weak baserom the table Kb = 1.2 × 10–6H2NNH2 + H2O º H2NNH3+ + OH– [H2NNH2] [H2NNH3+] [OH–]before 1.0 0 0at equilibrium 1.0 – x x x[ ]+-2 32 2263H NNH OHH NNH1.2 101.01.1 10pOH 2.96pH 14.00 pOHpH 11.04bKxxx−−    =× =−= ×== −=CHEM 1120 test 1 - Spring 2006Page 66. Calculate the pH of a solution in contact with solid Mg(OH)2. No other ions are present inthe water.a. 1.44 b. 4.48 c. 7.00 d. 9.52 e. 10.46Mg(OH)2 (s) º Mg2+ + 2OH-Ksp = 1.2 × 10–11X(Mg(OH)2 (s)) [Mg2+] [OH– ]before 1 0 0at equilibrium 1 x 2x( )+ - 221111 34-- 4[Mg ][OH ]1.2 10 21.2 10 41.44 10[OH ] 2[OH ] 2.9 10pOH = 3.54pH 10.46spKx xxxx−−−−=× =× == ×== ×=CHEM 1120 test 1 - Spring 2006Page 77. What is the molar solubility of BaF2?a. 7.5 × 10-3b. 4.2 × 10-16c. 1.0 × 10-5d. 1.5 × 10-2e. 2.7 × 10-16BaF2 (s) º Ba2+ + 2F-Ksp = 1.7 × 10–6X(BaF2 (s)) [Ba2+] [F-]before 1 0 0at equilibrium 1 x 2xBy definition, x is the molar solubility( )+ - 2266 33[Ba][F]1.710 21.710 47.510spKx xxx−−−=× =× == ×CHEM 1120 test 1 - Spring 2006Page 88. Calculate the pH of a mixture solution of 0.20 M NH3 and 0.20 M NH4ClO3.a. 11.23 b. 9.23 c. 7.00 d. 4.77 e. 2.35Notice that this is a 1:1 buffer of a weak base. Therefore the pOH = pKb..pOH = -log(1.71 × 10-5)pOH = 4.77pH = 9.23CHEM 1120 test 1 - Spring 2006Page 99. Calculate the pH of a mixture solution of 0.50 M NaCN and 0.10 M HCN.a. 2.50 b. 4.16 c. 4.85 d. 9.14 e. 9.84Notice that this is a buffer of a weak acid, but is not 1:1. Therefore pH . pKa but is not equal.HCN + H2O º CN– + H3O+Ka = 7.2 × 10–10[HCN] [CN–] [H3O+]before 0.10 0.50 0at equilibrium 0.10 - x 0.50 + x x( )- +31010[CN ][H O ][HCN]0.507.2 100.101.44 10pH =9.84aKx xxx−−=+× =−= ×CHEM 1120 test 1 - Spring 2006Page 1010. Calculate the pH of a 0.50 M solution of LiCH3COO.a. 4.55 b. 4.62 c. 5.55 d. 9.22 e. 9.38Notice that this is a salt of a weak acid. It is therefore a weak base!CH3COO– + H2O º CH3COOH + OH– The Kb for this reaction is given as:Kb(CH3COO–) = Kw/Ka(CH3COOH)Ka(CH3COOH) = 1.75 × 10-5[CH3COO–] [CH3COOH] [OH–]before 0.50 0 0at equilibrium 0.50 – x x x[ ]-3-3253CH COOH OHCH COO1.75 100.502.96 10pOH 2.53pH 14.00 pOHpH 11.47bKxxx−−  =  × =−= ×== −=CHEM 1120 test 1 - Spring 2006Page 1111. Calculate the pH of a 0.20 M solution of NH4ClO3.a. 10.34 b. 9.38 c. 9.03 d. 4.97 e. 4.62Notice that this is a salt of a weak base. Therefore it is a weak acid!NH4+ + H2O º NH3 + H3O+The Ka for this reaction is given as:Ka(NH4+) = Kw/Kb(NH3)Kb(NH3) = 1.71 × 10-5[NH4+] [NH3] [H3O+]before 0.20 0 0at equilibrium 0.20 – x x x[]+3 3+414 255NH H ONH1.00 101.71 10 0.201.08 10pH 4.97aKxxx−−−  =  ×=× −= ×=CHEM 1120 test 1 - Spring 2006Page 1212. Calculate the pH of a solution created by mixing 15.0 mL of 0.100 M KOH with 30.0 mL of0.100 M CH3COOH.a. 12.25 b. 9.23 c. 7.00 d. 4.76 e. 3.45Notice that the amount of the KOH is ½ that of the CH3COOH. Running the Arrhenius reactionone would therefore get equal amounts of the weak acid and its salt. This is therefore a 1:1buffer and the pH = pKa.Ka = 1.75 × 10-5pH = 4.76CHEM 1120 test 1 - Spring 2006Page 1313. Calculate the pH of a solution created by mixing 100 mL of 0.100 M HCl and 100 mL of0.100 M NH3.a. 9.38 b. 8.73 c. 5.27 d. 4.62 e. 3.24Notice that this is a weak base reacting with a strong acid is the right proportions. Therefore,there is no acid or base (Arrhenius) left over but rather just a salt. The dilution effect wouldmake the concentration 0.0500 M in NH4Cl and is a salt hydrolysis problem. SEE problem 11.Notice that this is a salt of a weak base. Therefore it is a weak acid!NH4+ + H2O º NH3 + H3O+The Ka for this reaction is given as:Ka(NH4+) = Kw/Kb(NH3)Kb(NH3) = 1.71 × 10-5[NH4+] [NH3] [H3O+]before 0.050 0 0at equilibrium 0.050 – x x x[]+3 3+414 256NH H ONH1.00 101.71 10 0.0505.4 10pH 5.27aKxxx−−−  =  ×=× −= ×=CHEM 1120 test 1 - Spring 2006Page 1414. A solution of Co(NH3)6Cl3 is at equilibrium with Co3+ and NH3(aq). The concentration of theNH3 is 0.50 M and the Co(NH3)63+ ion concentration is 0.0010 M. Calculate the concentrationof the Co3+ ion. (Kd(Co(NH3)63+) = 1.2 × 10-5 )a. 7.68 × 10–7 Mb. 3.0 × 10-2 Mc. 4.3 × 10-2 Md. 0.20 Me. 2.6 × 10-10 MThis is a type I problem.Co(NH3)63+ º Co3+ + 6 NH3( )3+ 633+3 663+53+ 7[Co ][NH ][Co(NH ) ][Co ] 0.501.2 100.0010[Co ] 7.68 10dK−−=× == ×CHEM 1120 test 1 - Spring 2006Page 1515. A solution of Co(NH3)6Cl3 is made up to be 0.10 M. Calculate the resultant concentration ofthe Co3+ ion. (Kd(Co(NH3)63+) = 1.2 × 10-5 )a. 4.3 × 10-2 Mb. 0.20 Mc. 7.68 × 10–7 Md. 2.6 × 10-10 Me. 3.0 × 10-2 MThis is a type II problem.Co(NH3)63+ º Co3+ + 6 NH3[Co(NH3)63+] [Co3+] [NH3]before 0.10 0 0at equilibrium 0.10 - x x 6 x( )3+ 633+3 6656 4 72[Co ][NH ][Co(NH ) ]61.2 100.101.2 10 4.67 103.0 10dKx xxxx−−−=× =−× = ×= ×CHEM 1120 test 1 - Spring 2006Page 1616. Which of the following ions is a spectator anion in an acid-base reaction?a. NO2– b. SO32– c. F– d. Na+e. ClO3– The anion of a strong acid is a spectator ion in an acid-base reaction!CHEM 1120 test 1 - Spring 2006Page 1717. Which of the