MCGRAW CHAPTER 19
Identify the major species in solution when the metal sulfide Ag2S dissolves in H2O. Select all that apply.
- OH- - HS- - Ag+
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
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
Which of the following statements correctly describe the solubility product constant Ksp for a slightly soluble substance? Select all that apply.
-Ksp is independent of the concentrations of the ions in solution. -Ksp depends on the temperature of the solution. -The value of Ksp indicates how far a dissolution equilibrium proceeds in favor of dissolved solute.
Which of the following combinations could be used in an acid- base buffer system?
-NH3/ NH4Cl -HNO2/ KNO2 -CH3COOH/ NaCH3COO-
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.
-Qsp = (0.025)2(0.075) -[SO42-] = 7.5 × 10-2 M
Which of the statements correctly describe selective precipitation? Select all that apply.
-Selective precipitation involves forming precipitates with specific classes of ions as a means for separation. -Selective precipitation is the separation of a mixture based upon the components' solubilities.
Which of the following options correctly describe the factors affecting buffer capacity? Select all that apply.
-The closer the ratio [HA]/[A−] is to 1, the higher the buffer capacity. -The more concentrated the buffer components, the greater the buffer capacity.
Which of the following is the correct Ksp expression for ZnS (s)?
Ksp = [Zn2+][HS-][OH-]
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 overall pH will decrease only slightly. -The ratio [HA]/[A−] will increase. -The [A-] in solution will decrease.
Which of the following statements correctly describe the titration curve for the titration of a strong acid with a strong base?
-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.
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
When comparing the titration curve for a weak acid- strong base titration and a strong acid- strong base titration the following differences are found.
-the curve for the weak acid- strong base titration rises gradually before the steep rise to the equivalence point. -the pH at the equivalence point is about 7.00 for the weak acid- strong base titration.
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
At the equivalence point for a weak acid-strong base titration, _______.
-the pH is greater than 7.00 -the pH is influenced largely by the conjugate base of the weak acid
Place the steps for preparing a buffer in the correct order, beginning with the first step at the top of the list.
1. Choose an appropriate conjugate acid-base pair 2. Use pH and pKa to determine the desired ratio of buffer component concentrations 3. Convert ratio to find the concentration of the two buffer components 4. Mix components together and correct pH if needed
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.
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.
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 the solution.
Buffer, Conjugate
Buffer _________ is a measure of the ability of a buffer to maintain pH following the addition strong acid or base.
Capacity
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
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-] = (1.9×10−70.0050) = 3.8 × 10-5 M.
Match each slightly soluble salt with the correct Ksp expression.
Fe(OH)2 = Ksp= [Fe2+][OH-]2 Fe(OH)3 =Ksp= [Fe3+][OH-]3
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
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-]
A slightly soluble ionic compound will dissolve to a small extent in H2O, and a saturated solution is formed at a fairly _______________ A slightly soluble ionic compound will dissolve to a small extent in H2O, and a saturated solution is formed at a fairly ________________ between undissolved solid and the dissociated ions in solution.
Low, Equilibrium.
Match the relationship between Qsp and Ksp to the correct description.
Qsp < Ksp = The solution is unsaturated and no precipitate forms. Qsp = The solution is saturated and no change occurs. Qsp > Ksp = Ksp A precipitate forms until the solution becomes saturated.
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 statements correctly describe a saturated solution of a slightly soluble ionic compound in H2O? Select all that apply.
The dissolved solute is assumed to be dissociated into ions. An equilibrium exists between the undissolved and dissolved solute.
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.
The S2- ion is so ______ that it completely reacts with water to form HS- and OH- ions in solution.
basic
the ph range over which the buffer is effective is called the ______ range. this range depends on the ______ concentrations of the buffer components, but usually btwn +/- ___ of the pKa of the acid component.
buffer, relative, 1
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
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.
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
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.
https://i.imgur.com/KRWJoA4.png
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
For a slightly soluble ionic compound such as Ag2SO4, Qsp= [Ag+]^2 [SO4^2-] 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
ion, solubility
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
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])
