Ionic Equilibria

Question 1

What is the Arrhenius Theory?

Answer 1

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

Arrhenius acid:
HCl → H+ + Cl-
H2SO4 → 2H+ + SO4 2-

Arrhenius base:
NaOH → Na+ + OH-
NA2O + H2O → 2Na + + 2OH-

Question 2

What is the Bronsted-Lowry Theory?

Answer 2

A bronsted acid is a proton donor
HCl → H+ + Cl-

A bronsted base is a proton acceptor
NH3 + H+ → NH4+
OH- + H+ → H2O

Question 3

What is the Lewis Theory?

Answer 3

A lewis base is an electron-pair acceptor
A lewis base is an electron-pair donor

H+ (acid) + :NH3 (base) → NH4+
H+ (acid) + :H2O (base) → H3O+

Question 4

What is a strong acid?

Answer 4

A strong acid is almost completely ionised or dissociated in aqueous solution
e.g. HCl, HBr, HI, oxoacids (H2SO4, HNO3, HClO4)

HCl + H2O → Cl- + H3O+

Question 5

What is a weak acid?

Answer 5

A weak acid is partially ionised or dissociated in aqueous solution
e.g. HF, HCN, H2S, organic acids (—COOH, —OH)

CH3COOH + H2O ⇌ CH3COO- + H3O+

Question 6

What is a strong base?

Answer 6

A strong base is almost completely ionised or dissociated in aqueous solution
e.g. Group 1 & 2 oxides/hydroxides (NaOH, Na2O, BaO, Ba(OH)2)

NaOH → Na+ + OH-

Question 7

What is a weak base?

Answer 7

A weak base is partially ionised or dissociated in aqueous solution
e.g. inorganic bases (MgO, NH3), organic bases (amides)

NH3 + H2O ⇌ NH4+ + OH-

Question 8

What is the degree of ionisation of weak acid/bases?

Answer 8

The degree of ionisation of weak acid/bases refers to the fraction of molecules that ionise in aqueous solution

α = (amount ionised)/(original amount)

α=1 for strong acids/bases
0<α<1 for weak acids/bases

Degree of dissociation increases with decreasing [acid] or [base]

Question 9

What is the Ka for weak monoprotic acid HA?
HA (aq) + H2O (l) ⇌ A- (aq) + H3O+ (aq)

Answer 9

Ka = [A-][H3O+] / [HA]
units: mol dm-3

Question 10

What is Ka and pKa?

Answer 10

Ka is the measure of strength of acid
pKa = -lg(Ka)

The stronger the acid, the larger the Ka, the smaller the pKa

Question 11

What is the Kb for weak monoprotic base B?
B (aq) + H2O (l) ⇌ BH+ (aq) + OH- (aq)

Answer 11

Kb = [BH+][OH-] / [B]
units: mol dm-3

Question 12

What is Kb and pKb?

Answer 12

Kb is the measure of strength of base
pKb = -lgKb

The stronger the base, the larger the Kb, the smaller the pKb

Question 13

What is Kw and pKw?

State the relationship of Kw with Ka and Kb

Answer 13

2 H2O (l) ⇌ [H3O+] + [OH-]
Kw = [H3O+][OH-]

At 25°C,
pKw = -lg(Kw) = 14.0

Kw = Ka x Kb

Question 14

What is pH of a solution?

Answer 14

The pH of a solution is the negative logarithm to abse 10 of the hydrogen ion concentration in mol dm-3

pH = -lg[H3O+]
The greater the [H3O+], the smaller the pH, the stonger the acid

Question 15

What is the relationship between Kw, pH, pOH?

Answer 15

pKw = pH + pOH = 14.0

Question 16

How do you calculate pH of weak acids?

Answer 16

[H3O+] = √Ka[HA]initial
pH = -lg[H3O+]

Question 17

How do you calculate pH of weak bases?

Answer 17

[OH-] = √Kb[B]initial
pOH = -lg[OH-]
pH = 14.0 - pOH

Question 18

What is the difference between the strength of acid vs pH of acid?

Answer 18

The strength depends on the extent of dissociation in aqueous solution
The pH depends on [H3O+] in aqueous solution

Question 19

stop at pg22 salt hydrolysis!