Acids and Bases

Question 1

Bronsted-Lowry acid?

Answer 1

proton donor

Question 1

Bronsted-Lowry base?

Answer 1

proton acceptor

Question 2

conjugate acid?

Answer 2

species formed when a proton is added to a base

Question 3

conjugate base?

Answer 3

species formed when a proton is removed from an acid

Question 4

Define buffer solution

Answer 4

solution that resists changes to pH when small amounts of an acid or a base is added

Question 5

Bronsted-Lowry acid-base reaction

Answer 5

reaction involving the transfer of a proton

Question 6

difference between monoprotic acid and diprotic acid

Answer 6

Monoprotic acid = acid that releases one H+ ion per molecule
e.g. HCl (hydrochloric acid), HNO3 (nitric acid), CH3COOH (ethanoic acid)

Diprotic acid = acid that releases two H+ ions per molecule e.g. H2SO4 (sulfuric acid), H2C2O4 (ethanedioic acid)

Question 7

definition of pH?

Rearrange it

How many decimal places should pH be given to?

Answer 7

pH = – log [H+]

[H+] = 10^-pH

2 d.p.

Question 8

[H2SO4] when pH = 1.30

Answer 8

[H+] = 10^-1.30 = 0.0501
[H2SO4] = 0.0501/2 = 0.0251

Question 8

ionic product of water expression?

value of kW

Answer 8

[H+][OH-]

1.00 x 10^-14

Question 9

Work out pH of strong acids

Work out pH of weak acids

Work out pH of acid buffers

Answer 9

Strong acids:
-use pH equation

Weak acids:
Use Ka, assume that [H+] = [OH-]

Acidic buffers:
-the above does not apply

Question 10

Why does Kw increase when temp increases?

Answer 10

ionisation of water is an endothermic pocess
water only very slightly dissociates

Question 11

Why does the expression for Kw not include concentration of water? (2 marks)

Answer 11

M1: [H2O] is very high
OR
very few H+ and OH- ions
OR
Only/very slightly dissociates

M2: [H2O] is relatively constant

Question 12

Which reaction is favoured when strong acids/bases dissociate?

Answer 12

Forward
More H+/OH- ions produced

Question 13

Which reaction is favoured when weak acids/bases dissociate?

Answer 13

Backwards
Less H+/OH- ions produced

Question 14

Acidic buffers are made from…
Give an example of an acidic buffer

Answer 14

Weak acid and its salt
E.g. ethanoic acid and sodium ethanoate

Question 15

Purpose of an acidic buffer is to…

Answer 15

-resist changes in pH keep the solution below pH 7

Question 16

What happens when we add H+ to buffer with ethanoic acid and its salt

Answer 16

H+ reacts with CH3COO- ions in solution
More CH3COOH produced
Equilibrium shifts to the left

Question 17

What happens when we add OH- to buffer with ethanoic acid and its salt

Answer 17

OH- ions react with H+
Lower concentration of H+
Equilibrium shifts to the right to replace the reacted H+ ions

Question 18

Basic buffers are made from…
Give an example of an basic buffer

Answer 18

Weak base and its salt
E.g. NH3 and NH4+Cl-

Question 19

Purpose of a basic buffer is to…

Answer 19

Resist changes in pH to keep the solution above pH 7

Question 20

What happens when we add OH- to a buffer with ammonia and ammonium chloride

Answer 20

OH- ions react with NH4+ ions
More NH3 and H2O produced
Equilibrium shifts to the left

Question 21

What happens when we add H+ to a buffer with ammonia and ammonium chloride

Answer 21

H+ reacts with OH-
Lower conc of OH-
Equilibrium shifts to the right