Florida International University s12

GENERAL CHEMISTRY 2 THIRD HOUR EXAM JUNE 20, 2011

Name ______

Panthersoft ID ______

Signature ______

Part 1 ______(28 points)

TOTAL______(100 points)

23 5 9 NA = 6.022 x 10 C = ( /9) (F - 32) F = ( /5)(C) + 32 1 amu = 1.661 x 10-27 kg C = K - 273.15 K = C + 273.15 1 atm = 760 torr = 760 mm Hg 1 atm = 1.013 bar pV = nRT R = 0.08206 L.atm/mol.K 1 L.atm = 101.3 J . 2 2 R = 8.314 J/mol K 1 J= 1 kg.m /s 2 2 1/2 n If ax + bx + c = 0, then x = ( - b  [b - 4ac] )/2a KP = Kc (RT) . -14 Ka Kb = Kw = 1.0 x 10 (at T = 25C) pH = pKa + log10{[base]/[acid]} H = E + pV G = H - TS DGrxn = DG°rxn + RT ln Q ln K = - DG°rxn/RT Do all of the following problems. Show your work. Part 1. Multiple choice. Circle the letter corresponding to the correct answer. There is one and only one correct answer per problem. [4 points each]

1) Which of the following reactions will go essentially to completion? a) Reaction of a strong acid with a strong base b) Reaction of a strong acid with a weak base c) Reaction of a weak acid with a weak base d) Both a and b e) Both a and b and c

2) Which of the following aqueous solutions would be a buffer solution? - a) A solution that has 0.100 M HNO2 (a weak acid) and 0.100 M NO2 - b) A solution that has 0.100 M HClO4 (a strong acid) and 0.100 M ClO4 + c) A solution that has 0.100 M NH3 (a weak base) and 0.100 M NH4 d) Both a and b e) Both a and c

3) Consider the titration of H3PO4, a weak polyprotic acid, with Ba(OH)2, a strong base. The number of equivalence points that will be observed in this titration is a) 3 b) 2 c) 1 d) 0 e) None of the above

4) In which of the following buffer solutions will the molar solubility of copper II hydroxide (Cu(OH) 2, Ksp = 2.2 x 10-20) be largest? a) A buffer solution at pH = 5.0 b) A buffer solution at pH = 7.0 c) A buffer solution at pH = 9.0 d) A buffer solution at pH = 11.0 e) The molar solubility will be the same in all of the above buffer solutions

5) For a process to be spontaneous which of the following must be true?

a) Ssyst > 0

b) Ssurr > 0

c) Suniv > 0 d) Both a and b e) Both a and b and c

6) For a particular chemical reaction Hrxn < 0 and Srxn < 0. The reaction a) will always be spontaneous b) will never be spontaneous c) will be spontaneous at low temperature but not at high temperature d) will be spontaneous at high temperature but not at low temperature e) Cannot tell from the information given

7) 1.000 mol of which of the following substances would be expected to have the largest value for S at T = 25. C?

a) CH4(g) b) CH3CH2OH(s)

c) CH3CH2OH(ℓ) d) CH3CH2OH(g) e) CH3CH2CH2CH2OH(g)

2 Note: In part 2 and part 3 of the exam you may assume T = 25.0  C in all of the problems.

Part 2. Short answer.

1) The following questions refer to the titration curve given below. For each of the following questions circle the correct answer. There is one and only one correct answer per question. [3 points each]

a) The titration curve shows the titration of

a strong acid a weak acid a strong base a weak base with a strong base with a strong base with a strong acid with a strong acid

b) Which point on the titration curve represents a region where a buffer solution has formed?

point A point B point C point D

c) Which point on the titration curve represents the equivalence point?

point A point B point C point D

d) Which of the following would be the best indicator to use in the titration?

erythrosin B methyl red bromthymol blue o-cresonphthalein

pKa = 2.9 pKa = 5.4 pKa = 6.8 pKa = 9.0

3 2) Define the following terms [4 points each]

a) endpoint

b) selective precipitation

-4 - 3) A buffer solution is formed using formic acid (HCOOH, Ka = 1.8 x 10 ) and formate ion (HCOO ). The concentration of formic acid in the buffer solution is twice the concentration of formate ion. What is the pH of the buffer solution? [4 points]

4) Consider the chemical reaction

2 A(g) + B(g) ⇄ A2B(g)

What is the difference, if any, between Grxn and Grxn? [4 points]

4 Part 3. Problems.

-8 1) A chemist has a 0.2000 M stock solution of hypochlorous acid (HClO, a weak acid, with K a = 2.9 x 10 ) and solid potassium hypochlorite (KClO, M = 90.55 g/mol), a strong electrolyte containing the conjugate base of hypochlorous acid. How many grams of KClO must be added to 1.000 L of the stock HClO solution to form a buffer solution with pH = 7.40? You may assume that the volume of the solution does not change when KClO is added. [12 points]

5 -13 2) The solubility product for lead II iodate (Pb(IO3)2 M = 557.0 g/mol) is Ksp = 2.6 x 10 .

a) What is the maximum amount of lead II iodate (in grams) that will dissolve in 1.000 L of pure water? [8 points]

b) What is the maximum amount of lead II iodate (in grams) that will dissolve in 1.000 L of a 0.200 M solution of sodium iodate (NaIO3), a soluble ionic compound? [8 points]

6 3) Transition metals can react with water to form hydroxide compounds. For example, the reaction of cobalt (Co) with water can be written as

Co(s) + 2 H2O(ℓ) ⇄ Co(OH)2(s)+ H2(g) K = p(H2)

Use the data below to find numerical values for the following: Grxn, Hrxn, Srxn, and K (the thermodynamic equilibrium constant). [16 points]

. Substance Hf (kJ/mol) Gf (kJ/mol) S (J/mol K)

Co(s) 0.0 0.0 30.0

Co(OH)2(s) - 537.9 - 454.3 79.0

H2(g) 0.0 0.0 130.7

H2O(ℓ) - 285.8 - 237.1 70.0