SmartBook Assignment Chapter 18: Acid-Base Equilibria and Solubility Equilibria
Formation of a stable complex ion will generally ______ the solubility of a sparingly soluble substance.
increase
Copper(II) sulfide (CuS) is sparingly soluble in water (Ksp = 6.0 x 10^-37). The addition of ammonia, which forms a stable complex ion with Cu2+, will _____ the solubility of copper sulfide in water.
increase, raise, heighten, or enlarge
A given mass of solid KOH is added to an aqueous solution of Cu(NO3)2 of known concentration. Select all the options that correctly reflect the information required to determine whether or not a precipitate forms in this solution.
Ksp of Cu(OH)2 The molar mass of KOH The volume of the Cu(NO3)2 solution
In a standard qualitative analysis scheme, cations in a solution can be separated by stepwise addition of precipitating agents from Group 1 to Group 2. Select the correct separation method for the Group listed. Select all that apply.
Add HCl will precipitate Group 1 cations. Adding H2S will precipitate Group 2 cations.
Which of the following statements correctly describe a strong acid-weak base titration curve? Select all that apply.
Before the equivalence point is reached, the weak base and its conjugate acid are both present in solution. The pH at the equivalence point is < 7.00.
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 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 combinations could be used in an acid-base buffer system? Select all that apply.
NH3 /NH4Cl HNO2 /KNO2 CH3COOH/NaCH3COO
Which of the following will NOT become more soluble if the pH of the solution is decreased? Select all that apply.
PbCl2 AgBr
Which slightly soluble ionic salts will become more soluble at lower pH?
Salts that contain the anion of a weak acid
Consider a buffer consisting of a weak acid (HA) and the corresponding conjugate base (A-). The buffer initially contains equal amounts of HA and A-. Match each picture to the correct representation of the buffer after the change indicated.
Strong acid has been added. ---- A Strong base has been added. ---- B
Which of the following descriptions are correct for an acid-base indicator? Choose all that apply.
The color of the indicator changes over a specific pH range. A typical indicator changes color over a range of about 1.5 - 2 pH units.
Consider the ionization of the weak acid HClO2: HClO2 (aq) + H2O (l) ⇌ ClO2- (aq) + H3O+ (aq) Select all the statements that correctly describe the effect of adding KClO2 to this system.
The solution pH will increase. The % ionization of HClO2 will decrease.
Select all the statements that correctly describe the solubility product constant Ksp for a slightly soluble substance.
The value of Ksp indicates how far a dissolution equilibrium proceeds in favor of dissolved solute. Ksp is a particular form of a general equilibrium constant (Kc).
Select the least soluble compound from the following list.
Zn(OH)2 (Ksp = 3 x 10^-16)
In the separation of 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.
0.5 M HNO3 and 0.5 M NaNO3 0.3 M HCl and 0.3 M NaOH
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.
1. Fe(NO3)3 2. Al(NO3)3 3. Ni(NO3)2 4. Mg(NO3)2
In order for a solution of a weak acid and its conjugate base to be an effective buffer, the ratio of weak acid to weak base (or vice versa) must be ______-fold or less.
10
For convenience, the number of significant figures used to report pH values is _____ (Recall that only those right of the decimal point are significant in a log value).
2 or two
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 × 10^-3 M
Which of the following is the correct Ksp expression for the reaction Al(OH)3 (s) ⇌ Al3+ (aq) + 3OH- (aq)?
Ksp = [Al^3+][OH-]^3
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.
Match the following points on the titration curve with the correct description.
A<--->Initial pH of acid, no base has been added. B<--->Half the amount of base needed to react with all the acid has been added. C<--->Enough base to react with all of the acid has been added. D<--->Excess base has been added.
Consider the following complex ion equilibria: Ag+ + 2NH3 ⇌ Ag(NH3)2+ Kf = 1.5 x 10^7 Ag+ + 2CN- ⇌ Ag(CN)2- Kf = 1.0 x 10^21 If a solution containing equal concentrations of both cyanide ions and ammonia was added to a solution of silver ions, which complex ion would form?
Ag(CN)2-
Select the statements that correctly describe how to calculate the pH at various points during the titration of a weak acid against a strong base.
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.
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
For a weak acid that has been dissolved in water, the ionization equilibrium will shift toward the reactants if a quantity of the conjugate base is added to the solution. This is an example of the _____ _____ effect.
Blank 1: common Blank 2: ion
For a weak acid that has been dissolved in water, the ionization equilibrium will shift toward the reactants if a quantity of the conjugate base is added to the solution. This is an example of the _____ _____effect.
Blank 1: common Blank 2: ion
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.
Blank 1: end Blank 2: equivalence
The solubility of a substance can be expressed in terms of the mass of the substance in _____ present in 1 L of a saturated solution, or in terms of the _____ solubility, which is the number of moles present in 1 L of a saturated solution.
Blank 1: grams or g Blank 2: molar
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 _____ in solution.
Blank 1: low, small, or dilute Blank 2: equilibrium Blank 3: ions or solute
A complex ion consists of a central _____ cation covalently bonded to two or more anions or molecules, which act as Lewis _____.
Blank 1: metal Blank 2: bases
For a buffer system composed of a weak acid-conjugate base, [H+] = Ka [HA]/[A−]. As long as the amounts of HA and A- are large relative compared to the amounts of OH- or H+ added, the change in [HA]/[A−] will be _____ and the change in [H+], and thus pH, will be _____.
Blank 1: small, tiny, or insignificant Blank 2: small, tiny, or insignificant
Consider the reaction PbSO4 (s) ⇌ Pb2+ (aq) + SO42- (aq). When Na2SO4 is added to the system, the presence of the common ion _____ (give the name or formula, including the charge) causes the equilibrium to shift toward the _____ and the solubility of PbSO4 will _____, in accordance with Le Chatelier's principle.
Blank 1: sulfate, or SO4^2- Blank 2: left, reactants, or reactant Blank 3: decrease or lessen
An indicator is a(n) _____ organic acid that has a different color than its _____ base. Each indicator changes color over a specific _____ range.
Blank 1: weak Blank 2: conjugate Blank 3: pH
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 conjugate base Ka of weak acid or Kb of weak base Concentration of weak acid
H2S gas is bubbled through a solution containing 0.10 M of each Co^2+, Cu^2+, and Fe^2+ ions. Which ion will precipitate first and what concentration of S^2- ions is required? Ksp values: CoS = 4 × 10^-21; CuS = 6 × 10^-37; FeS = 6 × 10^-19
Cu2+ will precipitate first, when [S2-] reaches 6 × 10^-36 M.
True or false: Qualitative analysis is the determination of the identity and amount of substance(s) present in a sample.
False
Which of the following statements describes the common ion effect?
For a solution of a weak acid in water, addition of the conjugate base will shift the ionization equilibrium.
Which of the following can affect the solubility of a sparingly soluble ionic compound?
Formation of complex ions Presence of a common ion Solution pH
Under what conditions will a precipitate not form when an aqueous solution of AgNO3 is added to an aqueous solution of NaCl?
If Q < Ksp
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
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
Which of the following statements correctly defines qualitative analysis?
Qualitative analysis is the determination of the types of ions present in a solution.
Consider the ionization of the weak acid HClO2: HClO2 (aq) + H2O (l) ⇌ ClO2- (aq) + H3O+ (aq) Select all the statements that correctly describe the effect of adding KClO2 to this system.
The % ionization of HClO2 will decrease. The solution pH will increase.
Fractional precipitation is a method of separating ions in aqueous solution. A reagent is slowly added that forms an insoluble salt with one or more of the ions present. Fractional precipitation is based on what property?
The Ksp value of the insoluble compounds.
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.
Select all the statements that correctly describe a saturated aqueous solution of a slightly soluble ionic compound that is in contact with undissolved solute.
The dissolved solute is assumed to be dissociated into ions. An equilibrium exists between the undissolved and dissolved solute.
Select all the options that correctly describe the formation constant (Kf) for a complex ion.
The larger the value for Kf, the more stable the complex ion. Kf is also known as the stability constant for the complex ion.
When comparing the titration curve for a weak acid-strong base titration and a strong acid-strong base titration the following differences are found. Choose 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 before the steep rise to the equivalence point.
When comparing the titration curve for a weak base-strong acid titration and a strong acid-strong base titration the following differences are found. Choose all that apply.
The pH at the equivalence point is below 7.00 for the weak base-strong acid titration. The curve for the weak base-strong acid titration drops gradually before the steep drop close to the equivalence point.
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.
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 weak acid component of the buffer should be close to the desired pH. The ratio of conjugate base to weak acid should be less than 10 and greater than 0.1.
Which statement correctly defines the equivalence point in an acid-base titration?
The point at which the number of moles of -OH added equals the number of H+ ions present
True or false: For complex ion formation, a Kf that is >> 1 indicates that a given complex ion is stable, and likely to form.
True
When Na2CO3 is added to a saturated solution of BaCO3, the equilibrium will shift so as to ______ the quantity of carbonate ions in solution, thus ______ the solubility of BaCO3.
decrease, decreasing
In an acid-base titration, the point at which equimolar amounts of acid and base have been combined is called the _____ point.
equivalence
The equilibrium constant Kf is known as the _____ constant for a complex ion, and measures the tendency of a metal ion to form a particular complex ion.
formation or stability
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
Compared to a strong acid-strong base titration, the curve for a weak acid-strong base titration begins at a ______ pH, and has a ______ vertical section as the equivalence point is reached.
higher; smaller
At the equivalence point of a weak acid-strong base titration, all the acid has been neutralized. However, the pH of the solution is not 7.0 because of the _____ of the conjugate base to produce OH- ions.
hydrolysis
At the equivalence point of a weak base-strong acid titration, all the base has been neutralized. However, the pH of the solution is not 7.0 because of the _____ of the conjugate acid to produce H3O+ ions.
hydrolysis, ionization, or dissociation
Adding a strong acid to a slightly soluble ionic compound will _____ its solubility if it contains the anion of a weak acid.
increase
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
Consider a buffer solution consisting of 1.0 M HF and 1.0 M NaF, which has an initial pH of 3.14 (Ka for HF = 7.2 × 10^-4). Use the Henderson-Hasselbalch equation to determine the new pH after 0.10 mol of NaOH is added to 1.0 L of this solution.
pH = 3.23
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)
Which of the following options correctly describes the function of an acid-base buffer?Consider a buffer made by combining equal volumes of 0.15 M CH3COOH and 0.32 M NaC2H3O2. What is the pH of this buffer if the Ka for CH3COOH is 1.8 × 10^-5?
pH = 5.07
Match the pH of the titration end point with the indicator that could be used to indicate the endpoint.
pH = 7.00<--->bromothymol blue pH = 2.00<--->thymol blue pH = 9.00<--->phenolphthalein
According to the Le Chatelier's principle, the addition of an ion in common with a weak acid will _____, thus changing the pH from that of the pure acid.
shift the equilibrium to the left
When a strong acid or base is added to a buffer system, there is a ______ change in the [HA]/[A−] ratio and thus a ______ change in pH.
small; small
For a slightly soluble ionic compound such as Ag2S, the expression Ksp = [Ag+]2[S2-] is called the _____ product constant for the compound.
solubility
For a slightly soluble ionic compound such as Ag2S, the expression Ksp = [Ag+]^2[S^2-] is called the _____ product constant for the compound.
solubility