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AP Chemistry Chapter 15 Assignment
Part I – Multiple Choice
1984
62. A student pipetted five 25.00–milliliter samples of hydrochloric acid and transferred each sample to
an Erlenmeyer flask, diluted it with distilled water, and added a few drops of phenolphthalein to
each. Each sample was then titrated with a sodium hydroxide solution to the appearance of the first
permanent faint pink color. The following results were obtained.
Volumes of NaOH Solution
First Sample ...................... 35.22 mL
Second Sample .................. 36.14 mL
Third Sample..................... 36.13 mL
Fourth Sample ................... 36.15 mL
Fifth Sample ...................... 36.12 mL
Which of the following is the most probable explanation for the variation in the student’s results?
(A) The burette was not rinsed with NaOH solution
(B) The student misread a 5 for a 6 on the burette when the first sample was titrated.
(C) A different amount of water was added to the first sample.
(D) The pipette was not rinsed with the HCI solution.
(E) The student added too little indicator to the first sample.
64. The net ionic equation for the reaction that occurs during the titration of nitrous acid with sodium
hydroxide is
(A) HNO2 + Na+ + OH– ⇄ NaNO2 + H2O
(B) HNO2 + NaOH ⇄ Na+ + NO2– + H2O
(C) H+ + OH– ⇄ H2O
(D) HNO2 + H2O ⇄ NO2– + H3O+
(E) HNO2 + OH– ⇄ NO2– + H2O
74. How many moles of NaF must be dissolved in 1.00 liter of a saturated solution of PbF 2 at 25°C to
reduce the [Pb2+] to 1 × 10–6 molar? (Ksp PbF2 at 25°C = 4.0 × 10–8)
(A) 0.020 mole
(B) 0.040 mole
(C) 0.10 mole
(D) 0.20 mole
(E) 0.40 mole
1989
35. When phenolphthalein is used as the indicator in a titration of an HCl solution with a solution of
NaOH, the indicator undergoes a color change from clear to red at the end point of the titration. This
color change occurs abruptly because
(A) phenolphthalein is a very strong acid that is capable of rapid dissociation
(B) the solution being titrated undergoes a large pH change near the end point of the titration
(C) phenolphthalein undergoes an irreversible reaction in basic solution
(D) OH– acts as a catalyst for the decomposition of phenolphthalein
(E) phenolphthalein is involved in the rate–determining step of the reaction between H3O+ and OH–
36. Appropriate laboratory procedures include which of the following?
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I. Rinsing a buret with distilled water just before filling it with the titrant for the first titration
II. Lubricating glass tubing before inserting it into a stopper
III. For accurate results, waiting until warm or hot objects have reached room temperature before
weighing them
(A)
(B)
(C)
(D)
(E)
II only
I and II only
I and III only
II and III only
I, II, and III
66. MnS(s) + 2 H+ ⇄ Mn2+ + H2S(g)
At 25°C the solubility product constant, Ksp, for MnS in 5 × 10–15 and the acid dissociation constants
K1 and K2 for H2S are 1 × 10–7 and 1 × 10–13, respectively. What is the equilibrium constant for the
reaction represented by the equation above at 25°C?
1 10
5 10
13
(A)
5 10
1 10
15
(B)
1 10
5 10
7
(C)
15
7
20
5 10
(D)
1 10
(E)
1 10
5 10
15
20
20
15
74. Equal volumes of 0.10–molar H3PO4 and 0.20–molar KOH are mixed. After equilibrium is
established, the type of ion an solution in largest concentration, other than the K+ ion, is
(A) H2PO4–
(B) HPO42–
(C) PO43–
(D) OH–
(E) H3O+
1994
65. Barium sulfate is LEAST soluble in a 0.01–molar solution of which of the following?
(A) Al2(SO4)3
(B) (NH4)2SO4
(C) Na2SO4
(D) NH3
(E) BaCl2
69. Correct procedures for a titration include which of the following?
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I. Draining a pipet by touching the tip to the side of the container used for the titration
II. Rinsing the buret with distilled water just before filling it with the liquid to be titrated
III. Swirling the solution frequently during the titration
(A)
(B)
(C)
(D)
(E)
I only
II only
I and III only
II and III only
I, II, and III
70. To determine the molar mass of a solid monoprotic acid, a student titrated a weighed sample of the
acid with standardized aqueous NaOH. Which of the following could explain why the student
obtained a molar mass that was too large?
I. Failure to rinse all acid from the weighing paper into the titration vessel
II. Addition of more water than was needed to dissolve the acid
III. Addition of some base beyond the equivalence point
(A)
(B)
(C)
(D)
(E)
I only
III only
I and II only
II and III only
I, II, and III
1999
Questions 9–12 refer to aqueous solutions containing 1:1 mole ratios of the following pairs of substances.
Assume all concentrations are 1 M.
(A) NH3 and NH4Cl
(B) H3PO4 and NaH2PO4
(C) HCl and NaCl
(D) NaOH and NH3
(E) NH3 and HC2H3O2 (acetic acid)
9.
10.
11.
12.
The solution with the lowest pH
The most nearly neutral solution
A buffer at a pH > 8
A buffer at a pH < 6
33. A 1.0 L sample of an aqueous solution contains 0.10 mol of NaCl and 0.10 mol of CaCl 2. What is
the minimum number of moles of AgNO3 that must be added to the solution in order to precipitate all
of the Cl– as AgCl(s) ? (Assume that AgCl is insoluble.)
(A) 0.10 mol
(B) 0.20 mol
(C) 0.30 mol
(D) 0.40 mol
(E) 0.60 mol
67. What is the molar solubility in water of Ag2CrO4? (The Ksp for Ag2CrO4 is 8 × 10–12.)
(A) 8 × 10–12 M
(B) 2 × 10–12 M
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(C)
4 10
12
M
(D)
3
4 10
12
M
(E)
3
2 10
12
M
71. In a qualitative analysis for the presence of Pb2+, Fe2+, and Cu2+ ions in aqueous solution, which of
the following will allow the separation of Pb2+ from the other ions at room temperature?
(A) Adding dilute Na2S(aq) solution
(B) Adding dilute HCl(aq) solution
(C) Adding dilute NaOH(aq) solution
(D) Adding dilute NH3(aq) solution
(E) Adding dilute HNO3(aq) solution
2002
36. A sample of a solution of an unknown was treated with dilute hydrochloric acid. The white precipitate
formed was filtered and washed with hot water. A few drops of potassium iodide solution were added
to the hot water filtrate and a bright yellow precipitate was produced. The white precipitate remaining
on the filter paper was readily soluble in ammonia solution. What two ions could have been present in
the unknown?
(A) Ag+(aq) and Hg22+(aq)
(B) Ag+(aq) and Pb2+(aq)
(C) Ba2+(aq) and Ag+(aq)
(D) Ba2+(aq) and Hg22+(aq)
(E) Ba2+(aq) and Pb2+(aq)
50. Which of the following represents acceptable laboratory practice?
(A) Placing hot objects on a balance pan
(B) Using distilled water for the final rinse of a buret before filling it with standardized solution
(C) Adding a weighed quantity of solid acid to a titration flask wet with distilled water
(D) Using 10 mL of standard solution for titration of 25 mL of acid solution
(E) Diluting a solution in a volumetric flask to its final concentration with hot water
63. Mixtures that would be considered buffers include which of the following?
I. 0.10 M HCl + 0.10 M NaCl
II. 0.10 M HF + 0.10 M NaF
III. 0.10 M HBr + 0.10 M NaBr
(A)
(B)
(C)
(D)
(E)
I only
II only
III only
I and II
II and III
65. Which of the following substances is LEAST soluble in water?
(A) (NH4)2SO4
(B) KMnO4
(C) BaCO3
(D) Zn(NO3)2
(E) Na3PO4
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69. If 200. mL of 0.60 M MgCl2(aq) is added to 400. mL of distilled water, what is the concentration of
Mg2+(aq) in the resulting solution? (Assume volumes are additive.)
(A) 0.20 M
(B) 0.30 M
(C) 0.40 M
(D) 0.60 M
(E) 1.2 M
2008
Questions 4-6
A solution of a weak monoprotic acid is titrated with a solution of a strong base, KOH. Consider the
points labeled (A) through (E) on the titration curve that results, as shown below.
4. Which point on the curve corresponds to the point at which the moles of the added strong base are equal
to the moles of the weak acid initially present?
5. Which point on the curve corresponds to the point at which the pH is closest to that of the strong base
being added?
6. Which point on the curve corresponds to the point at which the concentrations of the weak acid and its
conjugate base are approximately equal?
49. Salts containing which of the following ions are generally insoluble in cold water?
(A) Acetate
(B) Ammonium
(C) Potassium
(D) Nitrate
(E) Phosphate
Part II – Free Response
1970
(a) What is the pH of a 2.0 molar solution of acetic acid? Ka of acetic acid = 1.8 × 10-5
(b) A buffer solution is prepared by adding 0.10 liter of 2.0 molar acetic acid solution to 0.1 liter of a 1.0
molar sodium hydroxide solution. Compute the hydrogen ion concentration of the buffer solution.
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(c) Suppose that 0.10 liter of 0.50 molar hydrochloric acid is added to 0.040 liter of the buffer prepared
in (b). Compute the hydrogen ion concentration of the resulting solution.
1971
Solve the following problem
AgBr(s)
Ag+(aq) + Br-(aq)
Ksp = 3.3 10-13
Ag+(aq) + 2 NH3(aq)
Ag(NH3)2+(aq) K = 1.7 10+7
(a) How many grams of silver bromide, AgBr, can be dissolved in 50 milliliters of water?
(b) How many grams of silver bromide can be dissolved in 50 milliliters of 10 molar ammonia solution?
1972 (1)
Given a solution of ammonium chloride:
(a) What additional reagent or reagents are needed to prepare a buffer from the ammonium chloride
solution?
(b) Explain how this buffer solution resists a change in pH when:
(i) Moderate amounts of strong acid are added.
(ii) Moderate amounts of strong base are added.
(iii) A portion of the buffer solution is diluted with an equal volume of water.
1972 (2)
(a) How many moles of Ba(IO3)2 is contained in 1.0 liter of a saturated solution of this salt at 25 C. Ksp
of Ba(IO3)2 = 6.5 10–10
(b) When 0.100 liter of 0.060 molar Ba(NO 3)2 and 0.150 liter of 0.12 molar KIO3 are mixed at 25 C,
how many milligrams of barium ion remains in each milliliter of the solution? Assume that the
volumes are additive and that all activity coefficients are unity.
1973
A sample of 40.0 milliliters of a 0.100 molar HC 2H3O2 solution is titrated with a 0.150 molar NaOH
solution. Ka of acetic acid = 1.8 × 10–5
(a) What volume of NaOH is used in the titration in order to reach the equivalence point?
(b) What is the molar concentration of C2H3O2– at the equivalence point?
(c) What is the pH of the solution at the equivalence point?
1976
H2S + H2O ⇄ H3O+ + HS–
K1 = 1.0 × 10–7
–
+
2–
HS + H2O ⇄ H3O + S
K2 = 1.3 × 10–13
H2S + 2 H2O ⇄ 2 H3O+ + S2–
K = 1.3 × 10–20
+
2–
Ag2S(s) ⇄ 2 Ag + S
Ksp = 5.5 × 10–51
+
(a) Calculate the concentration of H3O of a solution which is 0.10 molar in H2S.
(b) Calculate the concentration of the sulfide ion, S2–, in a solution that is 0.10 molar in H2S and 0.40
molar in H3O+.
(c) Calculate the maximum concentration of silver ion, Ag+, that can exist in a solution that is 1.5 10–17
molar in sulfide ion, S2–.
1979
A solution of hydrochloric acid has a density of 1.15 grams per milliliter and is 30.0% by weight HCl.
(a) What is the molarity of this solution of HCl?
(b) What volume of this solution should be taken in order to prepare 5.0 liters of 0.20 molar
hydrochloric acid by dilution with water?
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(c) In order to obtain a precise concentration, the 0.20 molar hydrochloric acid is standardized against
pure HgO (molecular weight = 216.59) by titrating the OH – produced according to the following
quantitative reaction.
HgO(s) + 4 I– + H2O → HgI42– + 2 OH–
In a typical experiment 0.7147 grams of HgO required 31.67 milliliters of the hydrochloric acid
solution for titration. Based on these data what is the molarity of the HCl solution expressed to four
significant figures.
1982
A buffer solution contains 0.40 mole of formic acid, HCOOH, and 0.60 mole of sodium formate,
HCOONa, in 1.00 litre of solution. The ionization constant, Ka, of formic acid is 1.8 ×10–4.
(a) Calculate the pH of this solution.
(b) If 100. milliliters of this buffer solution is diluted to a volume of 1.00 liter with pure water, the pH
does not change. Discuss why the pH remains constant on dilution.
(c) A 5.00 milliliter sample of 1.00 molar HCl is added to 100. milliliters of the original buffer solution.
Calculate the [H3O+] of the resulting solution.
(d) A 800.-milliliter sample of 2.00-molar formic acid is mixed with 200. milliliters of 4.80-molar
NaOH. Calculate the [H3O+] of the resulting solution.
1983 (1)
The molecular weight of a monoprotic acid HX was to be determined. A sample of 15.126 grams of HX
was dissolved in distilled water and the volume brought to exactly 250.00 millilitres in a volumetric flask.
Several 50.00 milliliter portions of this solution were titrated against NaOH solution, requiring an average
of 38.21 milliliters of NaOH.
The NaOH solution was standardized against oxalic acid dihydrate, H 2C2O4.2H2O (molecular weight:
126.066 gram mol−1). The volume of NaOH solution required to neutralize 1.2596 grams of oxalic acid
dihydrate was 41.24 millilitres.
(a) Calculate the molarity of the NaOH solution.
(b) Calculate the number of moles of HX in a 50.00 milliliter portion used for titration.
(c) Calculate the molecular weight of HX.
(d) Discuss the effect of the calculated molecular weight of HX if the sample of oxalic acid dihydrate
contained a nonacidic impurity.
1983 (2)
(a) Specify the properties of a buffer solution. Describe the components and the composition of effective
buffer solutions.
(b) An employer is interviewing four applicants for a job as a laboratory technician and asks each how to
prepare a buffer solution with a pH close to 9.
Archie A. says he would mix acetic acid and sodium acetate solutions.
Beula B. says she would mix NH4Cl and HCl solutions.
Carla C.
says she would mix NH4Cl and NH3 solutions.
Dexter D. says he would mix NH3 and NaOH solutions.
Which of these applicants has given an appropriate procedure? Explain your answer, referring to your
discussion in part (a). Explain what is wrong with the erroneous procedures.
(No calculations are necessary, but the following acidity constants may be helpful: acetic acid, Ka =
1.8 × 10–5; NH4+, Ka = 5.6 × 10–10)
1984
Discuss the roles of indicators in the titration of acids and bases. Explain the basis of their operation and
the factors to be considered in selecting an appropriate indicator for a particular titration.
ap chem chapter 15 assignment
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1987 (1)
The percentage by weight of nitric acid, HNO3, in a sample of concentrated nitric acid is to be determined.
(a) Initially a NaOH solution was standardized by titration with a sample of potassium hydrogen
phthalate, KHC8H4O4, a monoprotic acid often used as a primary standard. A sample of pure
KHC8H4O4 weighing 1.518 grams was dissolved in water and titrated with the NaOH solution. To
reach the equivalence point, 26.90 millilitres of base was required. Calculate the molarity of the
NaOH solution. (Molecular weight: KHC8H4O4 = 204.2)
(b) A 10.00 milliliter sample of the concentrated nitric acid was diluted with water to a total volume of
500.00 milliliters. Then 25.00 milliliters of the diluted acid solution was titrated with the standardized
NaOH solution prepared in part (a). The equivalence point was reached after 28.35 milliliters of the
base had been added. Calculate the molarity of the concentrated nitric acid.
(c) The density of the concentrated nitric acid used in this experiment was determined to be 1.42 grams
per milliliter. Determine the percentage by weight of HNO3 in the original sample of concentrated
nitric acid.
1987 (2)
NH3 + H2O ⇄ NH4+ + OH− Ammonia is a weak base that dissociates in water as shown above. At 25ºC,
the base dissociation constant, Kb, for NH3 is 1.8x10−5.
(a) Determine the hydroxide ion concentration and the percentage dissociation of a 0.150 molar solution
of ammonia at 25ºC.
(b) Determine the pH of a solution prepared by adding 0.0500 mole of solid ammonium chloride to 100.
milliliters of a 0.150 molar solution of ammonia.
(c) If 0.0800 mole of solid magnesium chloride, MgCl2, is dissolved in the solution prepared in part (b)
and the resulting solution is well-stirred, will a precipitate of Mg(OH)2 form? Show calculations to
support your answer. (Assume the volume of the solution is unchanged. The solubility product
constant for Mg(OH)2 is 1.5x10−11.
1991
The acid ionization constant, Ka, for propanoic acid, C2H5COOH, is 1.3 × 10−5.
(a) Calculate the hydrogen ion concentration, [H+], in a 0.20-molar solution of propanoic acid.
(b) Calculate the percentage of propanoic acid molecules that are ionized in the solution in (a).
(c) What is the ratio of the concentration of propanoate ion, C 2H5COO−, to that of propanoic acid in a
buffer solution with a pH of 5.20?
(d) In a 100.-milliliter sample of a different buffer solution, the propanoic acid concentration is 0.35molar and the sodium propanoate concentration is 0.50-molar. To this buffer solution, 0.0040 mole
of solid NaOH is added. Calculate the pH of the resulting solution.
1993
The following observations are made about reaction of sulfuric acid, H2SO4. Discuss the chemical
processes involved in each case. Use principles from acid-base theory, oxidation-reduction, and bonding
and/or intermolecular forces to support your answers.
(a) When zinc metal is added to a solution of dilute H2SO4, bubbles of gas are formed and the zinc
disappears.
(b) As concentrated H2SO4 is added to water, the temperature of the resulting mixture rises.
(c) When a solution of Ba(OH)2 is added to a dilute H2SO4 solution, the electrical conductivity decreases
and a white precipitate forms.
(d) When 10 milliliters of 0.10-molar H2SO4 is added to 40 milliliters of 0.10-molar NaOH, the pH
changes only by about 0.5 unit. After 10 more milliliters of 0.10-molar H2SO4 is added, the pH
changes about 6 units.
1994
ap chem chapter 15 assignment
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A chemical reaction occurs when 100. milliliters of 0.200-molar HCl is added to 100. milliliters of 0.100molar Na3PO4 solution.
(a) Sketch a graph using the axes provided in your answer sheet, showing the shape of the titration curve
that results when 100. milliliters of the HCl solution is added slowly from a buret to the Na 3PO4
solution. Account for the shape of the curve.
(b) Write the equation for the reaction that occurs if a few additional milliliters of HCl are added the
solution resulting from the titration in (a).
1997
An experiment is to be performed to determine the mass percent of sulfate in an unknown soluble sulfate
salt. The equipment shown above is available for the experiment. A drying oven is also available.
(a) Briefly list the steps needed to carry out this experiment.
(b) What experimental data need to be collected to calculate the mass percent of sulfate in the unknown?
(c) List the calculations necessary to determine the mass percent of sulfate in the unknown.
(d) Would 0.20-molar MgCl2 be an acceptable substitute for the BaCl2 solution provided for this
experiment? Explain.
1998 (1)
Solve the following problem related to the solubility equilibria of some metal hydroxides in aqueous
solution.
(a) The solubility of Cu(OH)2(s) is 1.72 10−6 gram per 100. milliliters of solution at 25 C.
(i) Write the balanced chemical equation for the dissociation of Cu(OH)2(s) in aqueous solution.
(ii) Calculate the solubility (in moles per liter) of Cu(OH)2 at 25 C.
(iii) Calculate the value of the solubility-product constant, Ksp, for Cu(OH)2 at 25 C.
(b) The value of the solubility-product constant, Ksp, for Zn(OH)2 is 7.7 10−17 at 25 C.
(i) Calculate the solubility (in moles per liter) of Zn(OH)2 at 25 C in a solution with a pH of 9.35.
(ii) At 25 C, 50.0 milliliters of 0.100-molar Zn(NO3)2 is mixed with 50.0 milliliters of 0.300-molar
NaOH. Calculate the molar concentration of Zn2+(aq) in the resulting solution once equilibrium
has been established. Assume that volumes are additive.
1998 (2)
Answer the following using appropriate chemical principles.
When NH3 gas is bubbled into an aqueous solution of CuCl2, a precipitate forms initially. On further
bubbling, the precipitate disappears. Explain these two observations.
Justify your answer.
1998 (3)
ap chem chapter 15 assignment
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An approximately 0.1-molar solution of NaOH is to be standardized by titration. Assume that the
following materials are available.
• Clean, dry 50 mL buret
• 250 mL Erlenmeyer flask
• Wash bottle filled with distilled water
• Analytical balance
• Phenolphthalein indicator solution
• Potassium hydrogen phthalate, KHP, a pure solid monoprotic acid (to be used as the primary
standard)
(a) Briefly describe the steps you would take, using the materials listed above, to standardize the NaOH
solution.
(b) Describe (i.e., set up) the calculations necessary to determine the concentration of the NaOH solution.
(c) After the NaOH solution has been standardized, it is used to titrate a weak monoprotic acid, HX. The
equivalence point is reached when 25.0 mL of NaOH solution has been added. In the space provided
on your answer sheet, sketch the titration curve, showing the pH changes that occur as the volume of
NaOH solution added increases from 0 to 35.0 mL. Clearly label the equivalence point on the curve.
(d) Describe how the value of the acid-dissociation constant, Ka, for the weak acid HX could be
determined from the titration curve in part (c).
(e) The graph below shows the results obtained by titrating a different weak acid, H 2Y, with the
standardized NaOH solution. Identify the negative ion that is present in the highest concentration at
the point in the titration represented by the letter A on the curve.
2002
HOBr (aq) ⇄ H+ (aq) + OBr− (aq)
Ka = 2.3 × 10−9
Hypobromous acid, HOBr, is a weak acid that dissociates in water, as represented by the equation above.
(a) A solution of Ba(OH)2 is titrated into a solution of HOBr.
(i) Calculate the volume of 0.115 M Ba(OH)2(aq) needed to reach the equivalence point when
titrated into a 65.0 mL sample of 0.146 M HOBr(aq).
(ii) Indicate whether the pH at the equivalence point is less than 7, equal to 7, or greater than 7.
Explain.
(b) Calculate the number of moles of NaOBr(s) that would have to be added to 125 mL of 0.160 M HOBr
to produce a buffer solution with [H+] = 5.00 × 10−9 M. Assume that volume change is negligible.
2004
Answer the following questions relating to the solubilities of two silver compounds, Ag2CrO4 and
Ag3PO4.
Silver chromate dissociates in water according to the equation shown below.
Ag2CrO4(s) ⇄ 2 Ag+(aq) + CrO42–(aq) Ksp = 2.6 × 10–12 at 25°C
(a) Write the equilibrium-constant expression for the dissolving of Ag2CrO4(s).
(b) Calculate the concentration, in mol L–1, of Ag+(aq) in a saturated solution of Ag2CrO4 at 25°C.
ap chem chapter 15 assignment
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(c) Calculate the maximum mass, in grams, of Ag2CrO4 that can dissolve in 100.0 mL of water at 25°C.
(d) A 0.100 mol sample of solid AgNO3 is added to a 1.00 L saturated solution of Ag2CrO4. Assuming
no volume change, does [CrO42–] increase, decrease, or remain the same? Justify your answer.
In a saturated solution of Ag3PO4 at 25°C, the concentration of Ag+(aq) is 5.3 × 10–5 M. The equilibriumconstant expression for the dissolving of Ag3PO4(s) in water is shown below.
Ksp = [Ag+]3[PO43–]
(e) Write the balanced equation for the dissolving of Ag3PO4 in water.
(f) Calculate the value of Ksp for Ag3PO4 at 25°C.
(g) A 1.00 L sample of saturated Ag3PO4 solution is allowed to evaporate at 25°C to a final volume of
500.0 mL. What is the [Ag+] in the solution? Justify your answer.
2009
A buffer solution is prepared by dissolving some solid NaOCl in a solution of HOCl at 298 K. The pH of
the buffer is determined to be 6.48
(a) Calculate the value of [H3O+] in the buffer solution.
(b) Indicate which of HOCl(aq) or OCl–(aq) is present at the higher concentration in the buffer solution.
Support your answer with a calculation.
ap chem chapter 15 assignment