Chapter 17 (Buffers and Solubility)

Question 1

What is a buffer solution?

Answer 1

A buffer is a mixture of a weak acid and its conjugate base (and vice versa). It resists changes to pH.

Question 2

What is the A- in the Henderson-Hasselbach equation?

Answer 2

Base

Question 3

What is the HA in the Henderson-Hasselbach equation?

Answer 3

Acid

Question 4

What is the common ion effect?

Answer 4

The common ion effect is when the addition of a strong electrolyte sharing a common ion with a weak electrolyte will suppress its ionization.

Question 5

What is an electrolyte?

Answer 5

Substances that break apart into ions in water.

Question 6

What is a weak electrolyte?

Answer 6

Weak acids and bases.

Question 7

What is a strong electrolyte?

Answer 7

Strong acids, bases, and salts.

Question 8

Define titrant

Answer 8

A solution with a known concentration (this one is usually in the buret).

Question 9

What is Ksp?

Answer 9

The solubility product constant (sp). This tells you how much of that substance will dissolve in water.

Question 10

What is a ligand?

Answer 10

Ligands are ions or neutral molecules that bind to one central metal atom or ion (usually, the give away is the molecule in square brackets).

Question 11

Define buffering capacity

Answer 11

The ability of a buffer to resist pH changes when acid or base is added.

Question 12

Name the four types of titration combinations

Answer 12

1. Strong acid + strong base
2. Strong acid + weak base
3. Weak acid + strong base
4. Weak acid + weak base

Question 13

What effect does pH have on solubility?

Answer 13

If the ionic compound has a basic anion (OH-), decreasing the pH will also decrease the amount of (OH-) left in the solution. Then, according to Le Chatelier’s principle, this will shift the equilibrium to the right (dissolution). This increases solubility.

Question 14

If Q > Ksp, the compound will precipitate (True or False).

Answer 14

True; if Q is greater than K, this will force the reaction to favor the reactants, favoring precipitation (going until Q = Ksp).

Question 15

Is NaCl acidic, basic, or neutral?

Answer 15

Neutral; NaOH (SB) and HCl (SA) create a neutral salt.

Question 16

Is NH4Cl acidic, basic, or neutral?

Answer 16

Acidic; NH4OH (WB) and HCl (SA) create an acidic salt.

Question 17

Is CH3COONa acidic, basic, or neutral?

Answer 17

Basic; NaOH (SB) and CH3COOH (WA) create a basic salt.

Question 18

Define equivalence point.

Answer 18

Equivalence point is where # moles acid = # moles base.

Question 19

Define midpoint.

Answer 19

Where half of the analyte is neutralized. This is where there are equal amounts of HA and A-. Therefore, when we plug it in to the Henderson-Hasselbach equation, (A-/HA) = 1, and log(1) = 0. So at the midpoint, pH = pKa.

Question 20

What is the pKa?

Answer 20

The relative strength of an acid [-log(Ka)].