Exam: Ch 14 –17Number:

AP Cham (80 pts) I have not given, received, nor will give any aid on this exam.

Version ADPeriod: 2 3 4 5 March 2009

SECTION I: Multiple Choice (39 pts, 3 pts each): Choose the option that is the best answer or completes each question or statement. Write your answers in the blanks provided and erase mistakes completely. In this section, as a correction for haphazard guessing, one-fourth of the number of questions you answer incorrectly will be subtracted from the number of questions you answer correctly. NO CALCULATORS.

  1. A weak acid whose conjugate base is stronger than the acid itself.
  2. A buffer solution with pH>7
  3. A buffer solution with pH<7
  4. A solution with pH=7
  5. A weak base whose conjugate acid is stronger than the acid itself.

Acetic acid’s Ka =1.8 x 10-5

Ammonia’s Kb =1.8 x 10-5

  1. A solution containing 0.1 mols each of HC2H3O2 and NH3
  2. Ammonium ion, NH4+
  3. A solution containing 0.1 mols each of NH4Cl and NH3
  4. Which of the following is true about the titration of a weak acid with a strong base?
  1. The pH at the equivalence point is equal to 7.
  2. The pH at the equivalence point is greater than 7.
  3. The initial pH is extremely close to 0
  4. The pH curve rises gradually and then extremely abruptly near and around the equivalence point.
  5. More than one of these.
  1. How many milliliters of 5.0 M Ba(OH)2 are needed to titrate a solution containing 40.0 moles of phosphoric acid?
  1. 2.67
  2. 5.33
  3. 2670
  4. 5330
  5. 6000
  1. Which of the will cause an increase in the value of the equilibrium constant for an endothermic reaction?
  1. Increasing the Volume when there are more moles of gas on the products side.
  2. Increasing the temperature
  3. Adding a catalyst
  4. Adding moles of reactants
  5. More than one of these.
  1. Which of the following is/are amphoteric?
  1. NH3
  2. H2O
  3. Al(OH)3
  4. HSO4-
  5. More than one of these.
  1. Which of the following is the strongest acid?
  1. HAtO4
  2. HClO4
  3. HIO4
  4. HBrO4
  5. Cannot be determined.
  1. Which of the following acids could not exist(Hint: think about bonding from first semester)?
  1. HFO4
  2. H2CrO4
  3. HSbF6
  4. H2S2O8
  5. All of the above acids could theoretically exist.
  1. Which of the following relationships would produce a linear graph for a first order reaction?
  1. Log[X] vs. time
  2. 1/[x] vs. time
  3. ln k vs. T
  4. [X] vs. time
  5. None of the above.
  1. Which one of the following is true about the strength of oxyhalogen acids such as HOI, HIO2, HBrO2, etc?
  1. When the halogen is the same, the acid strength increases with the number of O’s.
  2. When the number of O’s are the same, acid strength increases as you go down the halogen group. (E.g. HOBr is stronger than HOCl).
  3. When the number of O’s are the same, acid strength decreases as you go down the halogen group. (E.g. HOCl is stronger than HOBr).
  4. A and B.
  5. A and C.
  1. The value of the rate constant for a reaction changes with…
  1. Changes in the concentration of the reactants
  2. Changes in temperature
  3. Addition of a catalyst
  4. B and C only
  5. A, B, and C
  1. Which one of the following is/are correct statements describing why a solution of sodium bicarbonate is basic.
  1. Sodium bicarbonate when dissolved in water forms sodium hydroxide and carbonic acid. Carbonic acid is a weak acid and sodium hydroxide is a strong base, thus making the solution basic.
  2. Sodium bicarbonate undergoes hydrolysis to form sodium hydroxide and carbonic acid. Carbonic acid is a weak acid and sodium hydroxide is a strong base, thus making the solution basic.
  3. The bicarbonate ion hydrolyzes according to the equation: HCO3- + H2O <----> H2CO3 + OH-, creating a basic solution.
  4. B and C only
  5. A, B, and C.

Section II: Free Response

  1. Consider the weak hypothetical oxyacid, hypoastatous acid, HOAt.

a)Write the equilibrium-constant expression for the ionization of HOAt in water.

b)The pH of a 0.45 M solution of HOAt is 4.99. Calculate the value of Ka for HOAt.

c)How many grams of NaOAt, sodium hypoastatate, must be added to 1.0 L of a 0.45 solution of HOAt to make the solution basic? Assume the change in volume due to the addition of solid NaOAt is negligible.

d)1.0 L of a 0.45 M solution of HOAt is titrated using 0.72 M CsOH. What is the pH when 50.0 mL of CsOH is added to the acid?

e)0.540 moles of solid NaOAt is added to the solution in d). The volume does change by an unknown amount.

f)Sketch the titration curve for the titration of 1.0 L of a 0.45 M solution of HOAt with 1.0 M CsOH solution. Remember to label important points(initial pH, buffering region, etc.) and the pH’s at those points.

g)Which of the following indicators will be appropriate for this titration? Justify your answer.

Indicator / pKb
B / 11.5
C / 7.0
D / 2.5

h)Will HOAt or HOBr be a stronger acid? Justify your answer in terms of bonding principles. You may use lewis diagrams.

  1. Consider the following data related to the kinetics of the reaction: A + B + C --> D

[A], mol L-1

/

[B], mol L-1

/

[C], mol L-1

/

Reaction rate, mol L-1 min-1

0.420

/

0.420

/

0.420

/

6.90 x 10-3

0.210

/

0.690

/

0.420

/

3.45 x 10-3

0.210

/

0.420

/

0.420

/

3.45 x 10-3

0.840

/

0.840

/

0.210

/

3.45 x 10-3

a)Write the rate law expression for this reaction.

b)Calculate the value of the rate constant, k. Be sure to include units.

c)(Extra credit): Derive one integrated rate law equation.

d)Consider the following mechanism :

A + C --> AB (slow)

AB + B --> D(fast)

Is AB a catalyst, intermediate, or neither? Justify your answer.

e)Is the mechanism correct according to the data the scientist collected? Justify your answer.

f)Suppose the reaction is exothermic. Suppose a catalyst is added to this reaction. Draw energy diagrams for both the catalyzed and uncatalyzed reactions using the same set of axes.

  1. The salt Lanthanum fluoride is quite insoluble in water. Its formula is LaF3.

a)Write a balanced net ionic equation showing LaF3 dissolving in water.

b)The molar solubility of LaF3 at 25 C is 1.2 x 10-7 mol L-1. Calculate the value of Ksp.

c)When the temperature is increased to 50 C, the solubility is 6.2 x 10-8. Predict whether the salvation process is endothermic or exothermic. Justify your answer.

d)50.0 mL of 4.50 M HF is added to 50.0 mL of a 0.0425 M solution of La(NO3)3. What, if anything, will take place in the beaker in which the two solutions are mixed? Justify your answer with a calculation.

e)The rate constant for the salvation process doubles when the temperature is increased from 50 C to 100 C. Calculate the activation energy for the salvation reaction.

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