SM-18.3, 18.4, 18.5

For a slightly soluble ionic compound such as Ag2S, the expression Ksp = [Ag+]2[S2-] is called the______ product constant for the compound.

Blank 1: solubility

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 Reason: The equivalence point is the point at which neutralization is complete. This occurs when equimolar amounts of acid and base have been combined.

Formation of a stable complex ion will generally ______ the solubility of a sparingly soluble substance.

increase

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

increase Reason: The anion of a weak acid is itself a weak base, which will react with the strong acid added. The equilibrium will shift to form more of the anion, increasing the solubility of the salt.

In calculations for acid-base titrations, pH values are usually reported to no more than:

2 places after the decimal

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: SO42-, sulfate, or SO4^2- Blank 2: left, reactants, or reactant Blank 3: decrease or lessen

An indictor is a ______ 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

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).

Blank: 2

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. Multiple select question. Moles of OH- in excess = 2.5 × 10-3

Moles of OH- in excess = 2.5 × 10-3 pH = 12.62 Moles of OH- added = 8.75 × 10-3

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.

Select all that apply 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. 1.) Ag2SO4 (Ksp = 1.5 x 10-5) 2.)PbI2 (Ksp = 7.9 x 10-9) 3.)Zn(OH)2 (Ksp = 3 x 10-16) 4.)BaF2 (Ksp = 1.5 x 10-6)

Zn(OH)2 (Ksp = 3 x 10-16)

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 not AgCl- Reason: Cl- is the anion of a strong acid, HCl, and will therefore not readily react with a strong acid to increase the solubility of AgCl.

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

1.) ksp = 8.7 x 10^-9 2.) ksp = 1.1 x 10^-10 3.) ksp = 6.3 x 10^-18

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.

1.2 × 10-3 moles of HClO remain in solution. 3.3 × 10-3 moles of OH- have been added. pH = -log(3.0 × 10-6) + log (3.3×10−3)/(1.2×10−3)

Calculate the molar concentration of Pb2+ ions at equilibrium in an aqueous solution of PbF2(s) if Ksp for PbF2is 3.6 x 10-8.

2.1 × 10-3 M Reason: Let [Pb2+] = x, then 3.6 × 10-8 = (x)(2x)2 = 4x3 and x = 3.6×10−84‾‾‾‾‾‾‾√3.

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- Reason: Formation of Ag(CN)2- is favored, since it has a much larger Kf value than Ag(NH3)2+.

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.

Assume [Pb2+]init = 0. Assume the change in solubility is small, so that [Cl-]eqm = 0.15. S = (1.7×10−5)/[(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 [IO−3]=2s. Ksp=4s3 Reason: Ksp must be divide by 4 before taking the cube root.

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.

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

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

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.

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 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.

Blank 1: formation or stability

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

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.

Blank 1: hydrolysis

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.

Blank 1: increase, raise, heighten, or enlarge

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

The solubility of MgCO3 in water at 25oC is equal to 1.6 x 10-3 g per 100 mL. Select the options that correctly reflect the steps required to calculate Ksp for this compound.

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

Which of the following can affect the solubility of a sparingly soluble ionic compound?

Formation of complex ions Solution pH Presence of a common ion

Select all that apply Which of the following are examples of complex ions?

HgCl42- Fe(SCN)(H2O)52+ Ag(NH3)2+

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

Match each point in a strong acid-base titration with the correct procedure for calculating the pH and/or [H3O+].

Initial pH: [H3O+] = [HA] and pH = -log[H3O+] Before equivalence point: Moles H3O+ remaining = (initial moles H3O+) - (moles H3O+ reacted); use total volume to calculate new [H3O+] and pH After equivalent point: Moles excess OH- present = (moles OH- added) - (moles OH- reacted); use total volume to calculate new [OH-]; calculate pH from pOH

Match each stage of a weak acid-strong base titration with the correct description of how to calculate [H3O+], [OH-], and/or pH.

Initial pH: use Ka and [HA]init to calculate [H3O+] = [A-] before equivalence point: pH = pKa + log[A−][HA]; [A-] = moles OH− addedtotal volume at equivalence point: [OH-] = Kb×[A−] where [A-] = after equivalence point: pH depends on moles excess OH- added

Select all the options that correctly describe the formation constant (Kf) for a complex ion.

Kf is also known as the stability constant for the complex ion. 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. The larger the value for Kf, the more stable the complex ion.

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 Reason: Ksp = (9.3 × 10-11)(2.8 × 10-10)3

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

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

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

PbCl2 AgBr Reason: Since Cl- is the conjugate base of a strong acid, it is not affected by decreasing pH. Reason: Br- is the anion of a strong acid and is not affected by decreasing pH. NOT Cu(OH)2 Reason: OH- is a strong base and reacts with H3O+ to form H2O. Cu(OH)2 will become more soluble at lower pH. NOT ZnS Reason: S2- is a strong base and reacts with H3O+ to form HS-. ZnS will become more soluble if the pH decreases.

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.

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

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

Salts that contain the anion of a weak acid Reason: The cation of a strong base generally does not react to any great extent with water. Addition of strong acid will have no effect in this case. Reason: In general cations are not weak bases. Reason: The cation of a weak base is a weak acid, which will not react with additional strong acid. Reason: The anion of a weak acid is itself a weak base, which will react with the strong acid added. The equilibrium will shift to form more of the anion, increasing the solubility of the salt.

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.

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 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 above 7.00 for the weak acid-strong base titration.

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 curve for the weak base-strong acid titration drops gradually before the steep drop close to the equivalence point. The pH at the equivalence point is below 7.00 for the weak base-strong acid titration.

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 the statements that correctly describe how to calculate the pH at various points during the titration of a weak acid against a strong base.

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.

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.

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.

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

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 Reason: Correct. The complex ion is the product of the equilibrium equation, so a large Kf value means that complex ion formation is favored.

Select all that apply Select all of the equations that correctly describe the steps required to calculate the concentration of free Ag+ remaining in solution when 0.10 mole of AgNO3 is added to 1.00 L of 0.60 M KCN. Kf for Ag(CN)2- = 1.0 × 1021.

[CN-] = 0.40 M ([Ag+][CN−]^2)/([Ag(CN)−2]) = 1.0 × 10^-21 (x(0.40)^2)/(0.10) = 1.0 × 10-21 [Ag(CN)2-] = 0.10 M

Match each condition with its effect on the solubility of a sparingly soluble ionic compound.

change in pH:Can either increase or decrease solubility, depending on the compound Addition of a common ion: Decreases solubility Formation pf a complex ion: Increases solubility

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 Reason: The equilibrium will shift to use up the excess CO32- ions, toward the undissociated salt, and the solubility of BaCO3 will decrease.

Match each term to the correct definition, with reference to an acid-base titration.

endpoint: the point at which the indicator changes color Equivalence point: the point at which the moles of -OH added are equal to the moles of H3O+ originally present

In an acid-base titration, the point at which equimolar amounts of acid and base have been combined is called the_______point.

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 Reason: The pH at the equivalence point in this type of titration is greater than 7.00. This is because the conjugate base of the weak acid interacts strongly with H2O to form additional OH- ions, making the solution 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

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 = (7.5×10−4)/(0.0400L) initial moles of H3O+ = 3.75 × 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 Reason: The overall charge of an ionic compound is always zero. The solubilities of two ionic compounds can meaningfully be compared using Ksp if the total number of ions in the formula is the same, for example, CaF2 and Ag2SO4, since both compounds have a total of 3 ions per formula unit. The larger the value of Ksp, the more soluble the compound. Reason: The overall charge of an ionic compound is always zero. The solubilities of two ionic compounds can meaningfully be compared using Ksp if the total number of ions in the formula is the same, for example, CaF2 and Ag2SO4, since both compounds have a total of 3 ions per formula unit.

Q > Ksp

precipitate forms until solution becomes saturated

Which of the following is the correct expression to calculate the molar solubility of Ag3PO4 in water at 25oC if Ksp = 2.6 × 10-18?

s = 4[square root] (2.6x10^-18)/27 Reason: [Ag+] = 3[PO43-] = 3s and Ksp = (3s)^3(s) = 27s^4

Match each term to its correct definition with regard to a slightly soluble ionic compound.

solubility: The number of grams of compound dissolved in a liter of saturated solution molar solubility: The number of moles of compound dissolved in a liter of saturated solution

Q = Ksp

solution is saturated and no change occurs

Q < Ksp

solution is unsaturated and no precipitate forms