Chapter 20 - Acids, Bases, and pH

Question 1

What is meant by a monobasic acid?

Answer 1

One H+ ion can be replaced
HNO₃

Question 2

What is meant by a dibasic acid?

Answer 2

Two H+ ions can be replaced
H₂SO₄

Question 3

What is meant by a tribasic acid and give an example

Answer 3

Three H+ ions can be replaced
H₃PO₄

Question 4

What is a Brønsted-Lowry acid?

Answer 4

Proton/H⁺ donor

Question 5

What is a Brønsted-Lowry base?

Answer 5

Proton/H⁺ acceptor

Question 6

Ultimately, what does an acid-base reaction involve?

Answer 6

A proton/H⁺ transfer

Question 7

An example:

Answer 7

Question 8

What is a conjugate acid-base pair?

Answer 8

Contains two species that can be interconverted by a transfer of a proton

Question 9

Example of a conjugate acid-base pair in a reaction

Answer 9

Question 10

What is the conjugate base of HNO₃?

Answer 10

NO₃⁻

Question 11

What is the conjugate acid of HPO₄²⁻?

Answer 11

H₂PO₄⁻

Question 12

What is the conjugate base of H₂O?

Answer 12

OH⁻

Question 13

What is the conjugate acid of CO₃²⁻

Answer 13

HCO₃⁻

Question 14

What are the conjugate acid/base pairs in the following equilibrium?

Answer 14

Question 15

When does dissociation only take place?

Answer 15

If water is present

Question 16

What is H₃O⁺ known as?

Answer 16

The hydronium ion
Active ingredient in many aqueous acid

Question 17

What is pH a measure of?

Answer 17

The concentration of H⁺ ions in solution

Question 18

How do we calculate the pH?

Answer 18

-log[H⁺ (aq)]

Question 19

What does a small value of pH suggest?

Answer 19

A large concentration of H⁺ ions in solution

Question 20

What is a change in pH by one unit equivalent to in terms of H⁺ concentration?

Answer 20

A 10x change

Question 21

How do we calculate the H⁺ concentration using pH?

Answer 21

10⁻ᵖᴴ

Question 22

What is a strong monobasic acid?

Answer 22

Completely dissociates in aqueous solution

Question 23

What must we assume for a strong monobasic acid?

Answer 23

[HA(aq)] = [H⁺(aq)]

Question 24

What is the acid dissociation constant?

Answer 24

Kₐ

Question 25

What is the expression for Kₐ for weak acids?

Answer 25

Question 26

How do we write this equation in terms of Kₐ?

Answer 26

Question 27

If the position of equilibrium is further to the right, what does this suggest about the weak acid?

Answer 27

The stronger it is

Question 28

What does a larger Kₐ value suggest?

Answer 28

The stronger the weak acid

Question 29

Is Kₐ temperature dependent?

Answer 29

Yes Normally standardised at 298K

Question 30

What do all Kₐ values usually have in common?

Answer 30

Very small values With negative indices Making it difficult to compare the strengths of acids

Question 31

Why do we convert Kₐ into pKₐ?

Answer 31

To make comparison of acids easier

Question 32

How do we calculate pKₐ?

Answer 32

-log Kₐ

Question 33

What does a smaller pKₐ value suggest?

Answer 33

The stronger the weak acid

Question 34

What must we assume for a strong monobasic acid?

Answer 34

[HA] = [H⁺]

Question 35

What must we assume for a weak acid?

Answer 35

[H⁺] ≠ [HA]

Question 36

How do we calculate the pH of weak acids?

Answer 36

Question 37

What are the two approximations we can use to simplify the equation of weak acids?

Answer 37

1. [H⁺] = [A⁻] 2. [HA]eqm = [HA]eqm

Question 38

What are the limitations with using approximations for Kₐ? ([H⁺] = [A⁻])

Answer 38

If pH > 6 then [H⁺] from the dissociation of water becomes more significant This approximation breaks down for very weak acids, or very dilute acids

Question 39

What is the value of [H⁺] at 25C and a pH value of 7?

Answer 39

1x10⁻⁷ mol dm⁻³

Question 40

What are the limitations with using approximations for Kₐ? ([HA]eqm = [HA]eqm)

Answer 40

This approximation holds for weak acids with small Kₐ values, but breaks down when [H⁺]eqm becomes more significant

Question 41

How do we determine the value of Kₐ from experiment?

Answer 41

Prepare a standard solution of the weak acid of known concentration Measure the pH of the standard solution using a pH meter

Question 42

Describe the ionisation of water

Answer 42

Ionises very slightly Acting as both an acid and a base

Question 43

How do we calculate the pH of pure water?

Answer 43

Kᵥᵥ = [H⁺][OH⁻]

Question 44

What is the value of Kᵥᵥ at 298K?

Answer 44

1 x 10⁻¹⁴mol² dm⁻⁶

Question 45

When is a solution neutral?

Answer 45

When [H⁺] = [OH⁻]

Question 46

When is a solution acidic?

Answer 46

[H⁺] > [OH⁻]

Question 47

When is a solution alkaline?

Answer 47

[H⁺] < [OH⁻]

Question 48

An acidic solution contains what?

Answer 48

OH⁻ ions

Question 49

An alkaline solution contains what?

Answer 49

H⁺ ions

Question 50

What is meant by a strong base?

Answer 50

Is an alkali that completely dissociates in solution Release OH⁻ ions