Equations Topic 8/18

Question 1

Definition of pH

Answer 1

pH = -log ([H+])
=>
[H+] = 10^-pH

Question 2

Water dissociation constant

Answer 2

Kw = [H+][OH-]

where
Kw = water dissociation constant

**values of Kw varies with temperature and can be found in the data booklet

Question 3

Negative log of Kw

Answer 3

pKw = pH + pOH
OR
pKw = pKa + pKb

Question 4

Acid and base dissociation constant

Answer 4

Ka = [H3O+][A-] / [HA] and Kb = [BH+][OH-] / [B]

where
Ka = acid dissociation constant
[H3O+] = proton concentration or hydronium ion concentration
[A-] = conjugate acid
[HA] = generic acid
[B] = generic base

**weak bases because weak bases don’t fully dissociate
**stronger weak bases have a larger Ka than weak weak acids. The other way around for weak bases

Question 5

negative log of acid and base dissociation constant

Answer 5

pKa = -lgKa and pKb = -lgKb

**lower pKa, stronger acid. weaker pKa, weaker acid