4.3 Acids and Bases

Question 1

What is a hydrogen ion identical to?

Answer 1

H+ is identical to a proton

Question 2

What is the Bronsted-Lowry definition of an acid?

Answer 2

A proton donor

Question 3

What is the Bronsted-Lowry definition of a base?

Answer 3

A proton acceptor

Question 4

What does “amphoteric” mean?

Answer 4

Can act as both an acid and a base

Question 5

According to the Bronsted-Lowry theory, when is an acidic substance an acid?

Answer 5

When a base is present

Question 6

What is an example of an amphoteric substance?

Answer 6

Water

Question 7

What is a conjugate acid formed from?

Answer 7

Formed from the ions of the base

Question 8

What pH numbers do acidic solutions have?

Answer 8

Less than 7 at 25C

Question 9

What is the pH of a neutral solution?

Answer 9

7 at 25C

Question 10

What pH numbers do basic solutions have?

Answer 10

Greater than 7 at 25C

Question 11

What is the equation for pH?

Answer 11

pH = -log[H+]

Question 12

What is the equation for [H+]?

Answer 12

[H+] = 10^(-pH)

Question 13

What is a strong acid?

Answer 13

A strong acid is fully dissociated in solution

Question 14

Why is HCl said to be monoprotic?

Answer 14

Because each molecule can donate just one proton

Question 15

Why is H2SO4 said to be diprotic?

Answer 15

Because each molecule can donate two protons

Question 16

What is the hydrogen ion concentration in 2.0M sulphuric acid?

Answer 16

4.0M

Question 17

What is a strong base?

Answer 17

A strong base is fully dissociated in solution

Question 18

What is the equation for Kw?

Answer 18

Kw = [H+][OH-]

Question 19

What is the value of Kw at 25C?

Answer 19

1 x 10^(-14)

Question 20

How can Kw be rewritten for pure water?

Answer 20

Kw = [H+]^2

Question 21

How can Kw be rearranged to find [H+] of pure water?

Answer 21

[H+] = √(Kw)

Question 22

What happens to the value of Kw as temperature increases? Why?

Answer 22

Kw increases as temperature increases due to the dissociation of water being endothermic

Question 23

What are weak acids and bases?

Answer 23

Weak acids and bases are partially dissociated in aqueous solution

Question 24

What is Ka?

Answer 24

Ka is the acid dissociation constant

Question 25

What is the equation for Ka?

Answer 25

Ka = ([H+][A-]) / ([HA])

Question 26

What is the equation for pKa?

Answer 26

pKa = -log(Ka)

Question 27

Why must Ka be taken into account when working out the pH of weak acids?

Answer 27

Because you cannot assume that the hydrogen ion concentration is the same as the acid concentration, due to it not dissociating fully

Question 28

How can Ka be rewritten for a weak acid?

Answer 28

Ka = [H+]^2 / [HA]

Question 29

How can Ka of a weak acid be rewritten to find [H+]?

Answer 29

[H+] = √(Ka X [HA])

Question 30

What are acid-base titrations used to find out?

Answer 30

They are used to find out the volumes needed to create a neutral solution

Question 31

What is a pH curve?

Answer 31

The graph of pH against volume of acid or base to create a neutral solution

Question 32

When does the equivalence point occur when the titration involves monoprotic acids and bases?

Answer 32

When there are equimolar amounts of acid and base present

Question 33

Where is the equivalence point with a strong acid into a strong base?

Answer 33

pH 7.0

Question 34

Where is the equivalence point with a strong acid into a weak base?

Answer 34

Below pH 7.0

Question 35

Where is the equivalence point with a weak acid into strong base?

Answer 35

Above pH 7.0

Question 36

Where is the equivalence point with a weak acid into weak base?

Answer 36

pH 7.0

Question 37

What are acid-base indicators?

Answer 37

Acid-base indicators are weak organic acids or bases

Question 38

Why is universal indicator unsuitable for use in titrations?

Answer 38

It is a mixture of four different indicators, giving it a range of different colours

Question 39

What is the general equation for an indicator?

Answer 39

HIn (aq) H+ (aq) + In- (aq)

Question 40

Only when will an indicator be effective in a particular indicator?

Answer 40

When its pH range matches the change in pH at equivalence

Question 41

What is the definition of a buffer?

Answer 41

A solution which resists small changes in pH when small amounts of acid or base are added to it, or when it is diluted

Question 42

What are some applications of buffers?

Answer 42

- to calibrate pH meters - to stop enzymes denaturing after being extracted - to achieve the correct conditions for dying fabrics - in shampoo to make the hair look smooth and shiny

Question 43

What does an acidic buffer contain?

Answer 43

A weak acid and its conjugate base

Question 44

What does a basic buffer contain?

Answer 44

A weak base and its conjugate acid

Question 45

What is the equation for working out the [H+] of a buffer?

Answer 45

[H+] + Ka x ([HA] / [A-])