08: ionic equilibria

Question 1

the Arrhenius theory

Answer 1

Arrhenius acids form hydrogen ions in aqueous solution and Arrhenius bases form hydroxide ions in aqueous solutions

Question 2

the Bronsted-Lowry Theory

Answer 2

Bronsted acid is a proton donor. A Bronsted base is a proton acceptor

Question 3

acid dissociation constant, Ka

Answer 3

for a weak monoprotic acid HA: HA + H2O ↔ A- (conj. base of HA) + H3O+

Ka = [products]/ [reactants]

Question 4

base dissociation constant, Kb

Answer 4

for a weak monoprotic base B: B + H2O ↔ BH+ (conj. acid of B) + OH-

Kb = [products]/ [reactants]

Question 5

pH of solution

Answer 5

the pH of a solution is the negative logarithm to base 10 of the hydrogen ion concentration in moldm-3

pH = -lg[H3O+]

Question 6

ionic product of water, Kw

Answer 6

water undergoes self-ionisation:
2H2O (l) -> H3O+ (aq) + OH- (aq)

Kw = [H3O+][OH-]
only at 25 degrees, Kw = 1.0 x 10-14 mol^2 dm-6

Question 7

buffer

Answer 7

a buffer solution can resist large changes in pH changes when small amounts of acid or base is added

Question 8

acidic buffer

Answer 8

weak acid and its conjugate base
eg. CH3COOH + H2O <-> CH3COO- + H3O+

Question 9

alkaline buffer

Answer 9

weak base and its conjugate acid
eg. NH3 + H2O <-> NH4+ + OH-

Question 10

types of indicator (2)

Answer 10

methyl orange (strong acid - weak base)
pH: 3.1-4.4 (red to yellow)

phenolphthalein (weak acid - strong base)
pH: 8.2 -10 (colourless to red)

Question 11

pH change at equivalence point for buffers

Answer 11

strong acid -strong base : 3-11
strong acid - weak base: 3-7 (excess acid)
strong base - weak acid:
7 -11 (excess base)
weak acid - weak base : none