2010 AP® CHEMISTRY FREE-RESPONSE QUESTIONS
CHEMISTRY
Section II
(Total time — 95 minutes)
Part A
Time — 55 minutes
YOU MAY USE YOUR CALCULATOR FOR PART A.
CLEARLY SHOW THE METHOD USED AND THE STEPS INVOLVED IN ARRIVING AT YOUR ANSWERS.
It is to your advantage to do this, since you may obtain partial credit if you do and you will receive little or no credit if
you do not. Attention should be paid to significant figures.
Be sure to write all your answers to the questions on the lined pages following each question in the booklet with the
pink cover. Do NOT write your answers on the green insert.
Answer Questions 1, 2, and 3. The Section II score weighting for each question is 20 percent.
1. Several reactions are carried out using AgBr, a cream-colored silver salt for which the value of the solubilityproduct constant, Ksp, is 5.0 x 10~13 at 298 K.
(a) Write the expression for the solubility-product constant, K , of AgBr.
(b) Calculate the value of [Ag+] in 50.0 mL of a saturated solution of AgBr at 298 K. S. 6 t
(c) A 50.0 mL sample of distilled water is added to the solution described in part (b), which is in a beaker with
some solid AgBr at the bottom. The solution is stirred and equilibrium is reestablished. Some solid AgBr
remains in the beaker. Is the value of [Ag41_greater than, less than, or equailQilifi .yalue_.youxalculatedin
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(d) Calculate the minimum volume of distilled water7irnifers~,Trecessary to completely dissolve a 5.0 g sample__
of AgBr(j) at 298 K. (The molar mass of AgBr is 188 g mol"1.) ^°1 - 0, OZ^^ * 7.1 x lo" 7 M LoU 37600 L \0l
(e) A student mixes 10.0 mL of 1.5 x 1Q~4 M AgNO3 with 2.0 mL of 5.0 x 10~4 M NaBr and stirs the resulting
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(f) Tfie'colbToTahoth'er salt of silver, Agl(i), is yellow. A student adds a solution STNaT to a test tube....."~
containing a small amount of solid, cream-colored AgBr. After stirring the contents of the test tube, the
student observes that the solid in the test tube changes color from cream to yellow.
(i) Write the chemical equation for the reaction that occurred in the test tube.
(ii) Which salt has the greater value of K : AgBr or Agl ? Justify your answer.
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CHAPTER 16 QUIZ A (Ksp)
1.
What is the solubility of barium sulfate in pure water at 25°C? (Ksp for
barium sulfate is 1.1 x 10~10)
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Calculate the solubility of magnesium hydroxide in 0.05 M. NaOH. (Ksp for
magnesium hydroxide is 1.1 x 10'11)
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Calculate the solubility product constant for pure PbSCU in water. The
solubility of PbSO4 is 1.25 x 10"4mol/L.
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Calculate the concentration of calcium ion and fluoride ion in a concentration
solution of calcium fluoride. (Ksp for calcium fluoride is 4.0 x 10"11)
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Will a precipitate form when 0.10 L of 8.0 X 10"3 M Pb(NO3)2 is added to
0.40 L of 5.0 X 10'3 M Na2SO4? (Ksp for lead sulfate is 6.3 x 10'7)
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AP Chemistry - Buffers and Common-Ion Effect Quiz
1 . In a 1 00. ml sample of a buffer solution, 0.35 M propanoic acid (C2H5COOH) is
mixed with 0.50 M sodium propanoate. Ka for propanoic acid is 1.3 x 10~5.
a. What is the pH of this buffer?
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b. To this buffer solution, 0.0040 moles of solid NaOH are added. Calculate
the pH of the resulting solution.
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c. If the concentrations of both the acid and the conjugate base were
doubled, how would pH be affected? Explain how the capacity of the
buffer is affected by this change in concentrations of the acid and base.
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2. A biochemist needs 750. ml of an acetic acid-sodium acetate buffer with pH
4.50. If the buffer is to be 0.15 M in CH3COOH, how many grams of CH3COONa
must be used? Ka for acetic acid is 1.8 x 10
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3.
What is the pH of a solution that is 0.25 M in ethylamine (C2H5NH2) and 0.30 M
in ethylammonium nitrate (C2H5NH3NO3)? Kb for ethylamine is 6.4 x 10"4.
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4. Which
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of the following would be the best combination of substances to create a buffer?
NaOH and HCI
HNO3 and NaNO3
NH3 and CH3NH3C1
HBrandNH 3
HN02andNaNO2
5. A solution of ammonia is mixed with a solution of ammonium chloride. Which of the
following statements is true?
a. The pH of the ammonia solution alone is less than the pH of the mixture.
b. The pH of the ammonia solution alone is more than the pH of the mixture.
c. The pH of the ammonia solution is the same as the pH of the mixture.
d. The pH of the mixture is 7.
e. Not enough information is given to determine the answer.
6. Which
a.
b.
c.
d.
e.
of the following will occur when a strong base is added to an acidic buffer?
The pH will increase rapidly.
The pH will increase slowly.
The pH will decrease rapidly.
The pH will decrease slowly.
The pH will become neutral and remain neutral.
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AP Chemistry - Titrations Quiz
1. C6H5NH2 (aq) + H2O (aq) o C6H5NH3+ (aq) + OH' (aq)
Aniline, a weak base, reacts with water according to the reaction represented above.
a. Write the equilibrium constant expression, Kb, for the reaction represented
above.
b. A sample of aniline is dissolved in water to produce 25.0 ml_ of 0.10 M
solution. The pH of the solution is 8.82. Calculate the equilibrium
constant, Kb, for this reaction.
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c. The solution prepared in part (b) is titrated with 0.10 M HCI. Calculate the
pH of the solution when 5.0 ml_ of the acid has been dispensed.
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d. Calculate the pH at the equivalence point of the titration in part (c).
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e.
The pKa values for several indicators are given below. Which of the
indicators listed is most suitable for this titration? Justify your answer.
Indicator
Erythrosine
Litmus
Thymolphthalein
pKa
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2. A 30.0 ml sample of 0.10 M hydrofluoric acid (HF, Ka = 6.8 x 10"4) is titrated to
the equivalence point with 15.0 ml of 0.20 M sodium hydroxide (NaOH.)
a. Sketch the curve that results when this titration is conducted. Ensure that
the shape of the curve and the pH values at the start of the titration, the
halfway point, and the equivalence point are relatively accurate.
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b. What is the pH at the halfway point in the titration? Explain.
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3. a. How many ml of 0.51 M HCI are required to titrate 35.0 ml of 0.33 M Ca(OH)2 to
the equivalence point?
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b. What is the pH at the equivalence point? Explain.
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