Chapter 16 Part 2

Question 1

What is a weak base?

Answer 1

A weak base only partially accepts H+ ions, generating an equilibrium mixture containing the intact weak base, hydroxide ion, and the conjugate acid of the weak base.

Question 2

Write the general equation for a weak base in water.

Answer 2

B(aq) + H2O(l) ⇄ OH-(aq) + HB+(aq)

Question 3

What is the equilibrium constant for a weak base denoted as?

Answer 3

Kb

Question 4

How is the equilibrium constant Kb expressed for a weak base?

Answer 4

Kb = Kc [H2O]

Question 5

What are common characteristics of weak bases?

Answer 5

Weak bases are often analogs of ammonia (NH3) or the conjugate bases of weak acids (can be anions).

Question 6

What is the relationship between Kb and pKb?

Answer 6

pKb = - log Kb

Question 7

How do you convert pKb to Kb?

Answer 7

Kb = 10^(-pKb)

Question 8

How do you calculate the pH of a weak base solution using its starting concentration and Kb?

Answer 8

Set up the equilibrium expression and solve for [OH-].

Question 9

What is the formula for percent ionization of a weak base solution?

Answer 9

% ionization = ( [OH- eq] / [initial concentration] ) x 100

Question 10

As the concentrations of a weak base solution decrease, what happens to the percent ionization?

Answer 10

The percent ionization increases.

Question 11

What is the threshold for making assumptions about percent ionization?

Answer 11

It is based on the number of significant figures needed for your answers.

Question 12

What is the approximate percent ionization when working with 2 significant figures?

Answer 12

< 10%

Question 13

What is the approximate percent ionization when working with 3 significant figures?

Answer 13

< 1%

Question 14

What is the approximate percent ionization when working with 4 significant figures?

Answer 14

< 0.1%