Chem 1225 Chapter 16

Adding a strong acid to a slightly soluble ionic compound will _____ its solubility if it contains the anion of a weak acid.

increase

A titration curve like the one shown, in which there is no buffer region and the pH at the equivalence point is 7, is characteristic of the titration of a ______ acid with a ______ base.

strong; strong

Which of the following is the correct Ksp expression for ZnS(s)?

Ksp = [Zn2+][HS-][OH-]

A slightly soluble ionic compound will dissolve to a small extent in H2O and a saturated solution is formed at a fairly _____solute concentration. At this point there is a(n) ____ between undissolved solid and the dissociated ions in solution.

Low Equilibrium

The solubility of Ag2CrO4 in water is equal to 0.029 g per 1 L of solution at 25oC. Which of the following options correctly reflect the steps required to calculate Ksp for this compound from the given information? Select all that apply.

Molar solubility = 0.029g1L0.029g1L x 1mol331.8g1mol331.8g = 8.7 x 10-5 M Ag2CrO4 Ksp = 2.5 x 10-12 [CrO42-] = 8.7 x 10-5 M

Which of the following statements correctly describe the molar solubility of a slightly soluble ionic compound?

Molar solubility is the number of moles of solute in 1 L of a saturated solution.

Under what conditions will a precipitate form when an aqueous solution of AgNO3 is added to an aqueous solution of NaCl?

If Q > Ksp

Which of the following statements about buffers are correct? Select all that apply.

A buffer consists of a weak acid in solution with its conjugate base. A buffer resists changes in pH from addition of acid or base.

Which of the following actions would cause a shift in the equilibrium system shown below? Select all that apply. PbCl2(s) ⇌ Pb2+(aq) + 2Cl-(aq)

Addition of Pb(NO3)2 to the system Addition of KCl to the system

In what way is the titration curve for a weak base-strong acid titration similar to the titration curve for a weak acid-strong base titration?

Both have a buffer region before the equivalence point is reached.

Which of the following conjugate acid-base pairs is the best choice to prepare a buffer of pH 4.30?

C6H5COOH/C6H5COONa (Ka of C6H5COOH = 6.3 × 10-5)

Which of the following statements correctly reflect the relationship between buffer composition and solution pH, given that Ka = [H3O+][A-][HA][H3O+][A-][HA]?

If the relative amount of HA is increased, the solution pH will decrease. The pH of the solution depends on the ratio [HA][A-][HA][A-].

Which of the following options correctly describe how to calculate the pH at various stages during the titration of a strong acid against a strong base? Select all that apply.

Initial pH = -log[HA]. At the equivalence point pH = 7.00.

Which of the following statements correctly describe the solubility product constant Ksp for a slightly soluble substance? Select all that apply.

Ksp depends on the temperature of the solution. The value of Ksp indicates how far a dissolution equilibrium proceeds in favor of dissolved solute. Ksp is independent of the concentrations of the ions in solution.

Which of the following will NOT become more soluble if the pH of the solution is decreased? Select all that apply.

PbCl2 AgBr

Consider the reaction PbSO4(s) ⇌ Pb2+(aq) + SO42-(aq). When Na2SO4 is added to the system the presence of the common ion _____ causes the equilibrium to shift toward the _____ and the solubility of PbSO4 will _____, in accordance with Le Chatelier's principle.

SO42-; reactants; decrease

Which slightly soluble ionic salts will become more soluble at lower pH?

Salts that contain a weakly basic anion

Which of the following statements correctly describe the titration curve for the titration of a strong acid with a strong base? Select all that apply.

The equivalence point is at a pH of 7.00. The pH rise is very steep close to the equivalence point of the titration.

Which statement is correct about the values of Q and Ksp for a solution of the slightly soluble ionic compound PbS?

The value of Ksp is a constant, while the value of Q can vary.

Select the least soluble compound from the following list.

Zn(OH)2 (Ksp = 1.8 x 10-14)

Which of the following salts will dissolve more readily in aqueous nitric acid than in pure H2O? Select all that apply.

Zn3(PO4)2 CaCO3 Fe(OH)3

There is a segment of a weak acid/strong base titration, prior to reaching the equivalence point, in which the weak acid is in solution with its conjugate base. During this phase of the titration, the pH of the solution can be calculated in the same way that one calculates the pH of ______.

a buffer

Identify the major species in solution when the metal sulfide Ag2S dissolves in H2O. Select all that apply.

Ag+ HS- H2S

In order to separate two ionic compounds by selective precipitation, a solution of a precipitating ion is added to the mixture until the Q of the _____ soluble compound is almost equal to its Ksp. This ensures that the Ksp of the _____ soluble compound is exceeded as much as possible and a maximum amount of it will precipitate.

more; less

A buffer used in food products is the benzoic acid/benzoate buffer, which has a pKa = 4.19. If you need to maintain a pH of 3.50 using this buffer system, what concentration of benzoate ion would you need if you have 0.05 M benzoic acid?

0.01 M benzoate ion

Which of the following can NOT be used as an acid-base buffer solution? Select all that apply.

0.3 M HCl and 0.3 M NaOH 0.5 M HNO3 and 0.5 M NaNO3

30.0 mL of a 0.25 M solution of HBr is titrated with a 0.20 M solution of NaOH. What is the pH of the solution after 15.0 mL of the NaOH solution has been added?

1.00

Which of the following NH3/NH4+ buffer systems has the highest buffer capacity? Assume that equal volumes of the solutions are mixed in each case.

1.00 M NH3/1.00 M NH4+

Calculate the molar concentration of Pb2+ ions at equilibrium in an aqueous solution of PbF2(s) if Ksp for PbF2 is 4.1 x 10-8. Assume that the F- ion will not hydrolize further in water.

2.2 x 10-3 M

30.0 mL of 0.35 M hydrofluoric acid (Ka = 6.8 x 10-4) is titrated with 0.25 M NaOH. What is the pH of the solution after 16.0 mL of the NaOH solution has been added?

2.96

The solubility of AgBr in water is 1.33 x 10-4 g/L at 25 oC. What is the value of Ksp for AgBr at this temperature?

5.0 x 10-13

An aqueous solution containing Ba2+ ions and SO42- ions is in equilibrium with solid BaSO4. The concentration of Ba2+ ions is 0.020 M. What is the concentration of SO42-? The value of Ksp for BaSO4 is 1.1 x 10-10.

5.5 x 10-9 M

What is the pH of a solution containing both 0.150 M HClO and 0.300 M NaClO? Ka for HClO is equal to 3.0 x 10-8.

7.82

A buffer is made up using 2.5 L of 0.25 M sodium phenolate (C6H5ONa) and solid phenol (C6H5OH; pKa = 10.0). The desired buffer pH is 9.82. Which of the following options correctly show the calculations required to calculate the mass of phenol needed? Select all that apply.

9.82 = 10.00 + log0.25[phenol]0.25[phenol] mass of phenol required = 2.5 L x 0.38mol1L0.38mol1L x 94.11g1mol94.11g1mol [phenol] = 0.2510-0.18

Which of the following options correctly describes the function of an acid-base buffer?

A buffer minimizes changes in pH when acid or base is added to the solution.

Which of the following statements correctly describe a saturated solution of a slightly soluble ionic compound in H2O? Select all that apply.

An equilibrium exists between the undissolved and dissolved solute. The dissolved solute is assumed to be dissociated into ions.

Select the options that correctly reflect the steps required to calculate the molar solubility of PbCl2 in 0.15 M NaCl if Ksp for PbCl2 = 1.7 x 10-5.

Assume [Pb2+]init = 0. Assume the change in solubility is small, so that [Cl-]eqm = 0.15. s = 1.7x10-5(0.15)2

Which of the following steps correctly show how to calculate the solubility for Pb(IO3)2 given that Ksp = 2.6 × 10-13? Select all that apply.

Assume that [Pb2+] = S, then [IO3-] = 2S. Ksp = 4S3

Which of the following statements correctly describe the equivalence point in an acid-base titration? Select all that apply.

At the equivalence point, the acid and base are completely neutralized. The indicator in an acid-base titration changes color near or at the equivalence point

Which of the following options correctly describe how to calculate the pH at various points during the titration of a weak acid against a strong base? Select all that apply.

At the equivalence point, the pH calculation is based on the reaction of the conjugate base A- with H2O. The initial [H3O+] is calculated from [HA]init and Ka. At the equivalence point, [A-] = initialmolesofHAtotalvolumeinitialmolesofHAtotalvolume.

Which of the following slightly soluble salts is more soluble in a 0.10 M HCl solution than it is in pure water?

BaCO3

The point in an acid-base titration in which equimolar amounts of acid and base have been added to the reaction is called the ___ point. The point at which an indicator in the titration changes color is called the ___ point.

Blank 1: equivalence Blank 2: end

Which of the following is the correct Ksp expression for the solution of Cr2(CO3)3 in water?

Ksp = [Cr3+]2[CO3-]3

Introduction of the common ion Br- by addition of KBr to the solution will _____ the value of Q for the reaction, which in turn will _____ the solubility of AgBr.

Blank 1: increase, raise, or enlarge Blank 2: decrease, lessen, lower, or reduce

A slightly soluble ionic compound will dissolve to a small extent in H2O and a saturated solution is formed at a fairly solute concentration. At this point there is a(n) between undissolved solid and the dissociated ions in solution.

Blank 1: low, small, dilute, or little Blank 2: equilibrium

In a homogeneous solution equilibrium system, all the reactants and products are in the same .

Blank 1: phase, state, or physical state

Which of the following options represent homogeneous equilibria? Select all that apply.

CH3COOH(aq) ⇌ H+(aq) + CH3COO-(aq) 2H2O(l) ⇌ H3O+(aq) + OH-(aq) 2NO2(g) ⇌ N2O4(g)

Rank the following compounds from greatest solubility (top of the list) to lowest solubility (bottom of the list).

Ca(OH)2 Ni(OH)2 Cu(OH)2

Which of the following combinations could be used in an acid-base buffer system? Select all that apply.

HNO2 /KNO2 NH3 /NH4Cl CH3COOH/NaCH3COO

Which of the following slightly soluble ionic compounds contain anions that will influence the pH of the resulting solution? Select all that apply.

HgF2 CaCO3 CoS

Ksp values can be used to determine the relative solubilities of ionic compounds that have the same number of ______ in their formulas.

Ions

Calculate the Ksp of Fe(OH)3 given the following equilibrium concentrations: [Fe3+] = 5.0 x 10-10 M and [OH-] = 1.3 x 10-9 M.

Ksp = 1.1 x 10-36

Which of the following is the correct Ksp expression for the reaction Al(OH)3(s) ⇌ Al3+(aq) + 3OH-(aq)?

Ksp = [Al3+][OH-]3

150 mL of 0.15 M Na2SO4 is mixed with an equal volume of 0.050 M AgNO3. Select all the options that correctly show the steps used to determine whether or not a precipitate will form, if Ksp for Ag2SO4 = 1.4 x 10-5.

Q = (0.025)2(0.075) [SO42-] = 7.5 x 10-2 M

Which of the following anions will hydrolyze in aqueous solution? Select all that apply.

S2- F-

Consider a general buffer system made from a weak acid, HA, and its conjugate base A-. Which of the following options correctly describe the behavior of this system when strong acid is added to it? Select all that apply.

The [A-] in solution will decrease. The ratio [HA][A-][HA][A-] will increase. The overall pH will decrease only slightly.

Which of the following options correctly explain why the initial [HA] can be used to approximate [HA] at equilibrium? Select all that apply.

The amount of H3O+ formed by ionization of the weak acid is very small compared to the initial concentration of the acid. The extent of ionization of a weak acid is very small.

Which of the following should be considered when selecting/preparing a buffer solution? Select all that apply.

The buffer capacity will be higher if more concentrated solutions are used. The pKa of the acid component of the buffer should be close to the desired pH.

If NaClO(aq) is added to the reaction shown below, which of the following statements would be true? Select all that apply. HClO(aq) + H2O(l) ⇌ ClO-(aq) + H3O+(aq

The concentration of HClO(aq) would increase. The pH of the solution would increase.

Consider a solution containing the weak acid HNO2 with its conjugate base in the form of NaNO2. What information must be known in order to calculate the pH of the solution using the Henderson-Hasselbalch equation?

The concentration of HNO2 The Ka of HNO2 The concentration of NaNO2

Why does the equivalence point for a weak base-strong acid titration occur at a pH < 7.00?

The conjugate acid of the weak base reacts with H2O to give a solution with pH < 7.00.

Consider a buffer solution consisting of 0.35 M HNO2 and 0.50 M KNO2, which has an initial pH of 3.50 (Ka for HNO2 = 4.5 x 10-4). If 0.03 mol of HCl are added to 1.0 L of this solution, which of the following options correctly reflect the steps required to calculate the change in pH? Select all that apply.

The final pH = 3.44. [H3O+] prior to the addition of HCl ≈ 4.5x10-4x0.350.504.5x10-4x0.350.50. [NO2-] after the addition of HCl is equal to 0.47 M.

A given mass of solid KOH is added to an aqueous solution of Cu(NO3)2. Select all the options that correctly reflect the information required to determine whether or not a precipitate forms in this solution.

The molar mass of KOH The volume of the Cu(NO3)2 solution The concentration of the Cu(NO3)2 solution Ksp of Cu(OH)2

The solubility of MgCO3 in water at 25oC is equal to 5.3 x 10-2 g per 100 mL. Select the options that correctly reflect the steps required to calculate Ksp for this compound.

The molar solubility will give both [Mg2+] and [CO32-]. Calculate the molar mass for MgCO3. Calculate molar solubility by converting g/100 mL to mol/L.

Which of the following options correctly describe the factors affecting buffer capacity? Select all that apply.

The more concentrated the buffer components, the greater the buffer capacity. The closer the ratio [HA][A-][HA][A-] is to 1, the higher the buffer capacity.

Which of the following options correctly describe the differences between the titration curve for a weak acid-strong base titration and a strong acid-strong base titration? Select all that apply.

The pH at the equivalence point is above 7.00 for the weak acid-strong base titration. The curve for the weak acid-strong base titration rises gradually through a buffer region before the steep rise to the equivalence point.

50.0 mL of a 0.040 M solution of Ca(NO3)2 is added to 50.0 mL of a 0.030 M solution of NaOH. Determine whether a precipitate of Ca(OH)2 will form by calculating the value of Q from the Ksp expression for Ca(OH)2. The value of Ksp for Ca(OH)2 is 6.5 x 10-6.

The value of Q is 4.5 x 10-6. A precipitate will not form.

True or false: A pH indicator is a weak acid or base that has a different color from its conjugate partner.

True

When a slightly soluble ionic compound such as PbCl2 is placed into water, ______.

an equilibrium is established between dissolved and undissolved solute

When Na2CO3 is added to a saturated solution of the sparingly soluble compound BaCO3, the equilibrium will shift by _____ the amount of barium ions in solution, thus _____ the solubility of BaCO3.

decreasing; decreasing

The _____ point of a titration is the point at which the indicator changes color. The indicator is chosen so that the color change occurs at a pH as close as possible to the pH of the _____ point.

end; equivalence

Which of the following are acceptable units of solubility and molar solubility of a slightly soluble ionic compound? Select all that apply.

g/L mol/L

When mixing solutions of Ca(NO3)2 and K2CO3, it is possible to determine whether a precipitate of CaCO3 will form by substituting the resulting concentrations of Ca2+ and CO32- into the Ksp expression to determine a value for Q. If the value of Q is ____than Ksp, a precipitate will form; if the value of Q is ____ than Ksp, then no precipitate will form.

greater less

The pH at the equivalence point for a weak acid-strong base titration is _____ than 7.00 because at this point the major species in solution is the conjugate _____ of the weak acid. This species reacts with H2O to form a(n) _____ solution.

greater; base; basic

30.0 mL of a 0.15 M solution of the weak acid HClO is titrated with 0.20 M NaOH. Which of the following options correctly reflect how to calculate the pH after the addition of 16.5 mL of NaOH? Select all that apply. (The equivalence point has not yet been reached.) Ka for HClO is equal to 3.0 x 10-6.

pH = -log(3.0 x 10-6) + log3.3x10-31.2x10-33.3x10-31.2x10-3 3.3 x 10-3 moles of OH- have been added. 1.2 x 10-3 moles of HClO remain in solution.

25.0 mL of 0.250 M HCl is titrated with a 0.125 M solution of the weak base aniline (C6H5NH2; Kb = 3.80 x 10-10). The equivalence point is reached when 50.0 mL of base has been added. Which of the following options correctly reflect the steps required to calculate the pH at the equivalence point? Select all that apply.

pH = 2.82 [C6H5NH3+] at the equivalence point = 6.25x10-30.025+0.050L6.25x10-30.025+0.050L = 8.33 x 10-2 M Ka of the conjugate acid C6H5NH3+ = 2.63 x 10-5

A buffer solution consists of 0.45 M HCOOH and 0.63 M HCOONa (pKa for HCOOH = 3.74). Which option shows the correct calculation for the pH of the buffer after 0.020 mol of solid NaOH is added to 1.0 L of the solution?

pH = 3.74 + log0.650.43

Which of the following is the correct expression for the Henderson-Hasselbalch equation, which is used to calculate the pH of an acid-base buffer solution?

pH = pKa + log([base][acid])

Select the correct expression to calculate the molar solubility of PbF2 in water at 25oC if Ksp = 3.6 x 10-8.

s = 3⎯⎯√3.6x10-84

Select the correct expression to calculate the molar solubility of Ag3PO4 in water at 25oC if Ksp = 2.6 x 10-18.

s = 4⎯⎯√2.6x10-1827

When a strong acid or base is added to a buffer system there is a ______ change in the [HA][A-][HA][A-] ratio and thus a ______ change in pH.

small; small

Buffer capacity is a measure of ______.

the amount of acid or base that a buffer can absorb without large changes in pH

Addition of acid to an equilibrium solution of a slightly soluble ionic compound will increase the solubility of the compound if ______.

the anion is a strong base the anion is a weak base