Chapter 20 Acids, bases and pH

Question 1

Describe a Bronsted-Lowry acid

Answer 1

Proton donors that release hydrogen ions when they’re in solution

Question 2

Describe a Bronsted-Lowry base

Answer 2

Proton acceptors that accept hydrogen ions when they’re in solution

Question 3

What are conjugate pairs?

Answer 3

Species that are linked by the transfer of a proton. They are always on opposite sides of the reaction equation

Question 4

Describe the difference between a conjugate base and a conjugate acid

Answer 4

A conjugate base is a species that has lost a proton

A conjugate acid is a species that has gained a proton

Question 5

What is the pH scale a measurement of?

Answer 5

Hydrogen Ion concentration

Question 6

What is the rule for strong Monobasic acids regarding concentrations?

Answer 6

For strong monobasic acids, [H+] == [Acid]

Question 7

Explain why for strong monobasic acids, [H+] == [Acid]

Answer 7

Strong monobasic acids fully ionise in solution which means one mole of acid produces one mole of hydrogen ions so the H+ concentration is the same as the acid concentration

Question 8

What is the ionic product of water equation

Answer 8

Kw = [H+][OH-]

Question 9

Describe the effect of changing concentration of [H+] or [OH-] for the value of Kw

Answer 9

Changing the concentration of [H+] or [OH-] in solution has no effect on the value of Kw as the equilbrium will shift if you change the concentration to keep the value of Kw the same

Question 10

Describe the effect of changing temperature of the solution for the value of Kw

Answer 10

Changing the temperature of the solution changs the value of Kw because dissociation of water is an endothermic process so for example warming the solution will shift the equilibrium to the right and Kw increases

Question 11

Describe the method using Kw to find the pH of a strong base

Answer 11

1. put all the values you are given into the expression for the ionic product of water, Kw
2. Rearrange the expression to find [H+]
3. Use the value of [H+] to find the pH of the solution

Question 12

What is Ka?

Answer 12

Ka is the Acid dissociation constant

Question 13

Why isnt [H+] the same as the acid concentration for weak acids?

Answer 13

Weak acids don’t fully ionise in solution so the concentration of H+ ions isn’t the same as the acid concentration

Question 14

Describe the two concentration assumptions that can be made regarding weak acids

Answer 14

1. The concentration of the acid at the start is the same as the concentration of the acid at equilibrium,
2. [H+] = [A-]

Question 15

What are the two equations that link pKa and Ka?

Answer 15

pKa = -log Ka
Ka = 10^-pKa

Question 16

What are the two equations that link pH and [H+]?

Answer 16

pH = -log[H+]
[H+] = 10^-pH

Question 17

What is a monobasic acid?

Answer 17

Acids that have only one proton that they can release into solution