Chapter 19 Ionic Equilibria in Aqueous Systems

What is the correct order of steps when preparing a buffer? 1. Choose an appropriate conjugate acid-base pair 2. Use pH and pKa to determine the desired ratio of buffer component concentration 3. Mix the components together and correct the pH if needed 4. Convert the ratio to find the concentration of the two buffer components

1, 2, 4, 3

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 reflects the steps required to calculate Ksp for this compound? A. Calculate molar solubility by converting g/100 mL to mol/L B. The molar solubility will give both [Mg 2+] and [CO3 2-] C. Calculate the molar mass for MgCO3 D. Temperature should be converted from C to K E. If [Mg 2+] = x, then [CO3 2-] = 2x.

A, B, C

Which of the following hydroxides will dissolve in basic solution? A. Zn(OH)2 (s) B. Fe(OH)3 (s) C. Al(OH)3 (s) D. Cu(OH)2 (s)

A, C

Which of the statements correctly describe selective precipitation? A. Selective precipitation is the separation of a mixture based upon the components' solubilities B. Selective precipitation can only be applied to a solution containing two different types of ions C. Selective precipitation involves forming precipitates with specific classes of ions as a means for separation D. Selective precipitation can be carried out with any solution containing a mixture of soluble ions without requiring any additional reagents

A, C

Which of the following descriptions is correct for an acid-base indicator? A. The color of the indicator changes over a specific pH range B. Indicators change color over a wide pH range C. A typical indicator changes color over a range of about 2 pH units D. Any mixture of a weak organic acid and its conjugate base can be used as an indicator E. Only a small amount of indicator is needed during a titration

A, C, E

Which of the following statements correctly describes a saturated solution of a slightly soluble ionic compound in H2O? A. The dissolved solute is assumed to be dissociated into ions B. There is a large amount of dissolved solute in a saturated solution C. There is no undissolved solute in a saturated solution D. An equilibrium exists between the undissolved and dissolved solute

A, D

Which of these describes what affects buffer capacity? A. The closer the ratio [HA]/[A-] is to 1, the higher the buffer capacity B. The stronger the acid or base in the conjugate acid-base pair, the higher the buffer capacity C. Two buffer solutions with the same pH will have the same buffer capacity D. The more concentrated the buffer components, the greater the buffer capacity

A, D

What is the correct description for A, B, C, and D

A. The 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 acids has been added D. Excess base has been added

What are the descriptions for points A, B, C, and D for the neutralization of the polyphonic acid H2SO3 with a strong base?

A. pH = pKa 1 B. The dominant species is HSO3- C. pH = pKa 2 D. The dominant species is SO32-

What are the descriptions for letters A, B, C, and D on the following titration curve for a polyphonic acid?

A. pKa 1 B. First equivalence point C. pKa 2 D. Second equivalence point

What is the relationship between Qsp and Ksp? A. Qsp < Ksp B. Qsp = Ksp C. Qsp > Ksp

A: The solution is unsaturated and no precipitate forms B: The solution is saturated and no change occurs C: A precipitate forms until the solution becomes saturated

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

Acid Base

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

What is considered when selecting/ preparing a buffer solution? A. The pH of the buffer will depend on the absolute concentrations of the acid and base solutions used B. The buffer capacity will be higher if more concentrated solutions are used C. The pKa of the acid component of the buffer should be close to the desired pH D. The pKb of the base component of the buffer should be close to the desired pH

B, C

Which of the following options correctly describes the differences between the titration curve for a weak acid-strong base titration and a strong acid-strong base titration? A. The weak acid-strong base titration curve has a greater pH range over the steep portion B. The curve for the weak acid-strong base titration rises gradually through a buffer region before the steep rise to the equivalence point C. The pH at the equivalence point is above 7.00 for the weak acid-strong base titration D. The initial pH for the weak acid-strong base titration is lower for the same initial concentration of acid

B, C

The solubility of Ag2CrO4 in water is equal to 0.029 g per 1 L of solution at 25 C. Which of the following options correctly reflects the steps required to calculate Ksp for this compound from the given information? A. [Ag +] = 4.35 x 10-5 M B. [CrO4 2-] = 8.7 x 10-5 M C. Molar solubility = (0.029g/ 1L) x (1mol/ 331.8g) = 8.7 x 10-5 M Ag2CrO4 D. Ksp = 2.5 x 10-12 E. Ksp = 2 x (8.7 x 10-5)^2 x (8.7 x 10-5)

B, C, D

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? A. Addition of 1.0 M NaOH (aq) B. Addition of 1.0 M HCl (aq) C. Addition of 1.0 M Fe(NO3)2 (aq) D. Addition of 1.0 M NaCN (aq)

B, D

Which of the following statements correctly describe the titration curve for the titration of a strong acid with a strong base? A. The pH rises slowly throughout the titration B. The equivalence point is at a pH of 7.00 C. The curve starts at a high pH and curves down as the base is added D. The pH rise is very steep close to the equivalence point of the titration

B, D

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.

Basic; Acidic; Zwitterion

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 solution

Buffer; Conjugate

Which of these correctly describes the function of an acid-base buffer? A. A buffer maximizes changes in pH when acid or base is added to the solution B. A buffer is used to determine if a precipitate is formed during a reaction C. A buffer minimizes changes in pH when acid or base is added to the solution D. A buffer is used to track pH changes during an acid-base titration

C

Which is true for a titration curve of a strong acid with a strong base? A. The curve starts at a high pH and curves down as the base is added B. The pH rises slowly throughout the titration C. The pH rise is very steep close to the equivalence point of the titration D. The equivalence point is at a pH of 7.00

C, D

Buffer _____ is a measure of the ability of a buffer to maintain the pH following the addition of strong acid or base

Capacity

What must be known in order to calculate the pH of an acid-base buffer solution using the Henderson-Hasselbalch equation?

Concentration of conjugate base Ka of a weak acid or Kb of a weak base Concentration of a weak acid

Consider the reaction PbSO4 (s) ⇌ Pb 2+ (aq) + SO4 2- (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.

SO4 2-; reactants; decrease

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

Salts that contain the anion of a weak acid

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

An indicator is a(n) _____ organic acid that has a different color than its _____ base. Each indicator changes color over a specific, narrow _____ range

Weak; Conjugate; pH

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.

acid; base; stronger

Amphoteric hydroxides are compounds that dissolve in both _____ and _____ solutions.

acidic; basic

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

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

complex

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

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

increase

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

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

What is the correct expression for the Henderson Hasselbalch equation? (Used to calculate the pH of an acid-base buffer solution)

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