CHM112 chapter 19
Amphoteric hydroxides are compounds that dissolve in both and solutions.
Blank 1: acidic or acid Blank 2: basic or base
The solubility of MgCO3 in water at 25°C is equal to 1.6 × 10-3 g per 100 mL. Which of the following options correctly reflect the steps required to calculate Ksp for this compound? Select all that apply.
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.
Equivalence point End point
The point at which the moles of OH- added are equal to the moles of H3O+ originally present The point at which the indicator changes color
A complex ion is formed between a metal ion and a ligand acting as a Lewis _____. When the ligand is a _____ Lewis species than H2O, the metal ion will form a complex ion with the ligand rather than with water.
base; stronger
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+
In calculations for acid-base titrations, pH values are usually reported to no more than _____.
2 places after the decimal
Calculate the molar concentration of Pb2+ ions at equilibrium in an aqueous solution of PbF2(s) if Ksp for PbF2 is 3.6 x 10-8.
2.1 x 10^3 M
Which of the following will NOT become more soluble if the pH of the solution is decreased? Select all that apply.
AgBr PbCl2
Fe(OH)2 Fe(OH)3
Ksp = [Fe2+][OH-]2 Ksp = [Fe3+][OH-]3
The S2- ion is so ______ that it completely reacts with water to form HS- and OH- ions in solution.
basic
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.
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
What is the buffer range for a buffer containing HBrO and KBrO, if the pKa for HBrO is 8.69?
7.69 - 9.69
Which of the following descriptions are correct for an acid-base indicator? Choose all that apply.
A typical indicator changes color over a range of about 2 pH units. The color of the indicator changes over a specific pH range. Only a small amount of indicator is needed during a titration.
For a slightly soluble ionic compound such as Ag2SO4, Qsp = [Ag+]2[SO42-] is called the -product expression. The value of Qsp for a saturated solution is the -product constant Ksp, which represents the equilibrium constant for the dissolution process at a given temperature.
Blank 1: ion Blank 2: solubility
A complex ion consists of a central ion covalently bonded to two or more anions or molecules, which are called .
Blank 1: metal Blank 2: ligands
pH = 7.00 pH = 1.00 pH = 9.00
Bromthymol blue Crystal violet Phenolphthalein
Which of the following is the correct Ksp expression for the reaction Al(OH)3 (s) ⇌ Al3+ (aq) + 3OH- (aq)?
Ksp = [Al3+][OH-]3
Which of the following is the most correct ion-product Ksp expression for the Na2S (s) compound in water?
Ksp = [Na+]2[HS-][OH-]
25.0 mL of a 0.20 M solution of the weak acid CH3COOH (Ka = 1.8 × 10-5) is titrated with 0.25 M NaOH. Place the steps required to calculate the pH at the equivalence point in the correct order, starting with the first step at the top of the list.
Mole volume CH3 OH- pH
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 curve for the weak acid-strong base titration rises gradually through a buffer region before the steep rise to the equivalence point. The pH at the equivalence point is above 7.00 for the weak acid-strong base titration.
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 pH of the solution would increase. The concentration of HClO (aq) would increase.
The pH at the equivalence point is below 7.00 for a weak base-strong acid titration. This is because the conjugate acid of the weak base hydrolyzes to produce ______ and the weak base.
hydronium ion
Adding a strong acid to a slightly soluble ionic compound will _____ its solubility if it contains the anion of a weak acid.
increase
Consider a buffer made by combining equal volumes of 0.15 M CH3COOH and 0.32 M NaCH3COO. What is the pH of this buffer if the Ka for CH3COOH is 1.8 x 10-5?
pH = 5.07
An amino acid contains a weakly amino group (NH2) and a weakly carboxyl group (COOH). At low pH both groups are protonated, but at physiological pH (pH = 7.2) the compound exists as a , a species with opposite charges on the same molecule.
Blank 1: basic Blank 2: acidic Blank 3: zwitterion
In a 0.75 M HF solution, the HF is 2.2% dissociated. When NaF (s) is added to this solution the percent dissociation of HF _____ and the pH of the resulting solution will be _____ than its original value. This effect is due to the addition of the common ion _____.
decreases; higher; F-
Strong acid has been added. Strong base has been added.
A B
The Ksp for Fe(OH)2 is 4.1 x 10-15. Which of the following procedures would increase the solubility of Fe(OH)2? Select all that apply.
Addition of 1.0 M HCl (aq) Addition of 1.0 M NaCN (aq)
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.
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
One type of acid-base buffer is composed of a weak , which will react with any added base, and its conjugate , which will react with any added acid.
Blank 1: acid Blank 2: base
Before the equivalence point in a weak acid-strong base titration curve, there is a gradually rising portion of the curve called the region. At this point in the titration, the weak acid and its base are both present in solution.
Blank 1: buffer Blank 2: conjugate
The pH range over which the buffer is effective is called the range. This range depends on the concentrations of the buffer components, but is usually within ± pH unit of the pKa of the acid component.
Blank 1: buffer Blank 2: relative or initial Blank 3: 1 or one
pH = 5.55 pH = 7.80 pH = 1.91
Methyl red Phenol red Thymol blue
Which of the following combinations could be used in an acid-base buffer system? Select all that apply.
NH3 /NH4Cl CH3COOH/NaCH3COO HNO2 /KNO2
Which slightly soluble ionic salts will become more soluble at lower pH?
Salts that contain the anion of a weak acid
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.
[HA][A−][HA][A-] increases [HA][A−][HA][A-] decreases
[H3O+] increases and pH decreases [H3O+] decreases and pH increases
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 = 1.5 × 10-5.
[SO42-] = 7.5 × 10-2 M Qsp = (0.025)2(0.075)
Rank the following compounds from greatest solubility (top of the list) to lowest solubility (bottom of the list). Instructions
-9 -10 -18
A buffer used in food products is the benzoic acid/benzoate buffer. Benzoic acid 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.
0.5 M HNO3 and 0.5 M NaNO3 0.3 M HCl and 0.3 M NaOH
The dissociation of H2S (aq) to produce sulfide ions S2- is often used as a simultaneous equilibrium to separate different metal ions whose sulfide solubilities vary widely. The [S2-] can be controlled by adjusting the pH of the solution to either precipitate the more soluble or the less soluble metal sulfide. The dissociation equation of hydrogen sulfide solution is: H2S (aq) + 2H2O (l) ⇌ 2H3O+ (aq) + S2- (aq). The Ksp of CdS is 1.0 × 10-24 and Ksp of MnS is 3 × 10-11 (at 25°C). Which sulfide compound would be preferentially precipitated in an acidic environment (i.e., H3O+ added)?
CdS
At the equivalence point for a weak acid-strong base titration, _______.
the pH is influenced largely by the conjugate base of the weak acid the pH is greater than 7.00
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 × 10-6.
3.3 × 10-3 moles of OH- have been added. pH = -log(3.0 × 10-6) + log3.3×10−31.2×10−33.3×10-31.2×10-3 1.2 × 10-3 moles of HClO remain in solution.
The solubility of a slightly soluble ionic compound can be increased by adding a ligand (molecule or ion) that forms a(n) ion with the metal cation.
Blank 1: complex
In order to simplify calculations involving slightly soluble ionic compounds, we assume that the small amount of dissolved solute completely into separate in solution.
Blank 1: dissociates or separates Blank 2: ions
In an aqueous strong acid-strong base titration, the point occurs when the number of moles of OH- ions added is equal to the number of moles of H3O+ initially present.
Blank 1: equivalence
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
An indicator is a(n) organic acid that has a different color than its base. Each indicator changes color over a specific, narrow range.
Blank 1: weak Blank 2: conjugate Blank 3: pH
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.
Initial pH Before equivalence point At equivalence point After equivalence point
Calculate [H3O+] using Ka and [HA]initial. pH = pKa + log[A-][HA] Calculate [OH-] using Kb and [A-]; [H3O+] = Kw[OH-]. pH depends on excess base added.
Which of the following quantities must be known in order to calculate the pH of an acid-base buffer solution using the Henderson-Hasselbalch equation? Select all that apply.
Concentration of weak acid Concentration of conjugate base Ka of weak acid or Kb of weak base
A dilute solution of NaCl is added dropwise to a solution containing 0.0050 M Cu+ and 0.0025 M Pb2+. Which metal chloride will precipitate first? Ksp of CuCl = 1.9 × 10-7 and Ksp of PbCl2 = 1.7 × 10-9 (at 25oC)
CuCl ; Precipitation will begin when [Cl-] = 1.9×10−70.00501.9×10-70.0050 = 3.8 × 10-5 M.
6 M NaOH is added to a solution of each of the following salts. All the solutions contain the same concentration of metal ion. Arrange the solutions in the order in which a precipitate will form, with the first solution to form a precipitate at the top of the list. Instructions
Fe Al Ni Mg
Identify the major species in solution when the metal sulfide Ag2S dissolves in H2O. Select all that apply.
HS- OH- Ag+
Consider the reaction PbSO4 (s) ⇌ Pb2+ (aq) + SO42- (aq). When can Ksp values be used to compare the relative solubilities of two ionic compounds?
If the formulas of the compounds contain the same total number of ions
When can Ksp values be used to compare the relative solubilities of two ionic compounds?
If the formulas of the compounds contain the same total number of ions
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.
Match the following points on the titration curve with the correct description. A B C D
Initial pH of acid, no base has been added. Half the amount of base needed to react with all the acid has been added. Enough base to react with all of the acid has been added. Excess base has been added.
Calculate the Ksp of Fe(OH)3 given the equilibrium concentrations [Fe3+] = 9.3 × 10-11 M and [OH-] = 2.8 × 10-10 M.
Ksp = 2.0 × 10^39
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.
Ksp = 2.5 x 10^12 Molar solubility = 0.029g1L0.029g1L x 1mol331.8g1mol331.8g = 8.7 x 10-5 M Ag2CrO4 [CrO42-] = 8.7 x 10-5 M
Which of the following is the correct Ksp expression for ZnS (s)?
Ksp = [Zn2+][HS-][OH-]
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.
Mass of phenol required = 2.5 L x 0.38mol1L0.38mol1L x 94.11g1mol94.11g1mol [phenol] = 0.2510−0.180.2510-0.18 9.82 = 10.00 + log0.25[phenol]
A chemist titrates a 25.00-mL portion of 0.25 M HNO3 with a 0.25 M solution of NaOH. Which of the following options correctly reflect the steps required to calculate the pH once 35.00 mL of NaOH has been added? Select all that apply.
Moles of OH- in excess = 2.5 × 10-3 Moles of OH- added = 8.75 × 10-3 pH = 12.62
Why does the pH of a buffer solution change relatively little when strong acid or base is added to it? Select all the correct explanations.
Most of the excess H3O+ or OH- is absorbed by the resulting shift in equilibrium. The ratio [HA][A−][HA][A-] changes relatively little due to the shift in equilibrium.
Which of the following options correctly reflect the steps required to calculate the molar solubility of PbCl2 in 0.15 M NaCl if Ksp for PbCl2 = 1.7 × 10-5? Select all that apply.
S = 1.7×10−5(0.15)21.7×10-5(0.15)2 Assume [Pb2+]init = 0. Assume the change in solubility is small, so that [Cl-]eqm = 0.15.
Which of the following options correctly reflect the steps required to calculate the molar solubility of MgCO3 in 0.010 M Mg(NO3)2 if Ksp for MgCO3 = 3.5 × 10-8? Select all that apply.
S = 3.5×10−80.0103.5×10-80.010 Assume the presence of the common ion Mg2+ reduces the solubility of the MgCO3. Assume the change in solubility is small so [Mg2+]eqm = 0.10. Assume the [Mg2+] is entirely from the strong electrolyte Mg(NO3)2
Which of the statements correctly describe selective precipitation? Select all that apply.
Selective precipitation is the separation of a mixture based upon the components' solubilities. Selective precipitation involves forming precipitates with specific classes of ions as a means for separation.
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.
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.
The initial [H3O+] is calculated from [HA]init and Ka. At the equivalence point the pH calculation is based on the reaction of the conjugate base A- with H2O. At the equivalence point, [A-] = initial moles of HAtotal volumeinitial moles of HAtotal volume.
Which of the following statements correctly reflect the relationship between buffer composition and solution pH given that Ka = [H3O+][A−][HA][H3O+][A-][HA]? Select all that apply.
The pH of the solution depends on the ratio [HA][A−][HA][A-]. If the relative amount of HA is increased, the solution pH will decrease.
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 pH rise is very steep close to the equivalence point of the titration. The equivalence point is at a pH of 7.00.
Which of the following should be considered when selecting/preparing a buffer solution? Select all that apply.
The pKa of the acid component of the buffer should be close to the desired pH. The buffer capacity will be higher if more concentrated solutions are used.
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 a strong acid is added to it? Select all that apply.
The ratio [HA][A−][HA][A-] will increase. The overall pH will decrease only slightly. The [A-] in solution will decrease.
Qsp < Ksp Qsp = Ksp Qsp > Ksp
The solution is unsaturated and no precipitate forms. The solution is saturated and no change occurs. A precipitate forms until the solution becomes saturated.
Consider the dissociation of the weak acid HClO2, which can be represented by the balanced equation HClO2 (aq) + H2O (l) ⇌ ClO2- (aq) + H3O+ (aq). Which of the following options correctly describe the effect of adding solid KClO2 to this system? Select all that apply.
The solution pH will increase. The % dissociation of HClO2 will decrease.
Which of the following statements correctly describe the solubility product constant Ksp for a slightly soluble substance? Select all that apply.
The value of Ksp indicates how far a dissolution equilibrium proceeds in favor of dissolved solute. Ksp depends on the temperature of the solution. Ksp is independent of the concentrations of the ions in solution.
A given mass of solid KOH is added to an aqueous solution of Cu(NO3)2. Which of the following options correctly reflect the information required to determine whether or not a precipitate forms in this solution? Select all that apply.
The volume of the Cu(NO3)2 solution Ksp of Cu(OH)2 The molar mass of KOH
In what way is the titration curve for a weak base-strong acid titration different to the titration curve for a weak acid-strong base titration?
The weak base-strong acid titration curve will have an equivalence point at pH < 7.00.
Which of the following hydroxides will dissolve in basic solution? Select all that apply.
Zn(OH)2 (s) Al(OH)3 (s)
Which of the following salts will dissolve more readily in aqueous nitric acid than in pure H2O? Select all that apply.
Zn3(PO4)2 Fe(OH)3 CaCO3
Initial pH Before equivalence point After equivalence point
[H3O+] = [HA] and pH = -log[H3O+] Moles H3O+ remaining = (initial moles H3O+) - (moles H3O+ reacted); use total volume to calculate new [H3O+] and pH Moles excess OH- present = (moles OH- added) - (moles OH- reacted); use total volume to calculate new [OH-]; calculate pH from pOH
Consider a buffer solution consisting of 0.30 M NaF and 0.30 M HF, which has an initial pH of 3.18. Ka for HF = 6.6 x 10-4. If 10. mL of a 2.0 M NaOH solution are added to 1.0 L of this buffer, select all the options that correctly reflect the steps required to calculate the change in pH.
[H3O+]new = 6.6 x 10-4 x 0.280.320.280.32 pHnew = -log(6.6×10−4×0.320.28)6.6×10-4×0.320.28= 3.24
An amino acid has a COOH group, which is a weak _____, and an NH2 group, which is a weak ____. At _____ pH both groups are protonated, but at physiological pH (around 7.00) the compound exists as a zwitterion, a species with opposite charges on the same molecule.
acid; base; low
The ______ is the pH range where a buffer effectively neutralizes added acids and bases while maintaining a relatively constant pH.
buffer range
Place the steps for preparing a buffer in the correct order, beginning with the first step at the top of the list. Instructions
chose use convert mix
In order to simplify Ksp calculations, we often assume that any amount of a slightly soluble ionic compound that dissolves in solution has ______.
completely dissociated into separate ions
When Na2CO3 is added to a saturated solution of BaCO3, the equilibrium will shift by _____ the amount of barium ions in solution, thus _____ the solubility of BaCO3.
decreasing; decreasing
Consider a buffer solution consisting of 0.35 M HNO2 and 0.50 M KNO2, which has an initial pH of 3.30 (Ka for HNO2 = 7.1 x 10-4). If 0.030 mol of HCl are added to 1.0 L of this solution, select all the options that correctly reflect the steps required to calculate the change in pH.
pH = -log(7.1×10−4×0.380.47)7.1×10-4×0.380.47 = 3.24 [H3O+] = 7.1 x 10-4 x 0.380.47
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])
Match the letter given on the following titration curve with the description for the neutralization of the polyportic acid H2SO3 with a strong base. A B C D
pH = pKa1 The dominant species is HSO3-. pH = pKa2 The dominant species is HSO3-.
Match the letter given on the following titration curve for a polyprotic acid with the description. A B C D
pKa1 First equivalence point pKa2 Second equivalence point
In the titration of a strong acid with a strong base, the equivalence point occurs when ______.
the number of moles of added OH- ions equals the number of moles of H3O+ initially present
The typical number of significant figures in reported pH values is ______ digits after the decimal point in acid-base titrations.
two
Under what conditions will a precipitate definitely not form when an aqueous solution of AgNO3 is added to an aqueous solution of NaCl?
If Qsp < Ksp
A complex ion is formed between a metal ion, acting as a Lewis , and a ligand acting as a Lewis . When the ligand is a Lewis base than H2O, the metal ion will form a complex ion with the ligand rather than with water.
Blank 1: acid Blank 2: base Blank 3: stronger, better, or greater
Select the least soluble compound from the following list.
Zn(OH)2 (Ksp = 3 x 10-16)
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
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
A chemist titrates a 25.00-mL portion of 0.15 M HCl with a 0.20 M solution of KOH. Which of the following options correctly describe how to calculate the pH at the beginning of this titration AND after 15.00 mL of base has been added? Select all that apply.
initial pH = -log(0.15) = 0.82 [H3O+] after base has been added = 7.5×10−40.0400L7.5×10-40.0400L initial moles of H3O+ = 3.75 x 10-3
For ionic compounds that have the same total number of _____ in their formulas, the larger the Ksp value, the _____ soluble the compound.
ions; more
Consider the equilibrium system NH3 (aq) + H2O (l) ⇌ NH4+ (aq) + OH- (aq). If some solid NH4Cl were added to the system, the equilibrium would shift to the _____ and the [OH-] would _____.
left; decrease
A complex ion consists of a central _____ ion covalently bonded to two or more anions or molecules, which are called _____.
metal; ligands
In order to separate two ionic compounds by selective precipitation, a solution of a precipitating ion is added to the mixture until the Qsp 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 solution consists of 0.23 M HF and 0.31 M NaF (pKa for HF = 3.18). Which option shows the correct calculation for the pH of the buffer using the Henderson-Hasselbalch equation after 0.010 mol of HCl is added to 1.0 L of the solution?
pH = 3.18 + log 0.30/0.24
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 + log 0.65/0.43
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 is a measure of the ability of a buffer to maintain the pH following the addition of strong acid or base.
Blank 1: capacity
Which of the following conjugate acid-base pairs is the best choice to prepare a buffer of pH 3.50?
HCOOH/HCOONa (pKa of HCOOH = 3.74)
Which of the following is the correct expression to calculate the molar solubility of Ag3PO4 in water at 25°C if Ksp = 2.6 × 10-18?
S = 4√ 2.6×10−1827
Sulfides can be separated selectively from solution by adjusting the pH. Addition of strong acid causes the [HS-] to _____ and the _____ soluble sulfide will precipitate. Strong base, which has the opposite effect to strong acid, causes the ____ soluble sulfide to precipitate.
decrease; less; more
