15 Acid-Base Equilibria Flashcards
Arrhenius Theory
An acid is a compound that dissolves in water to yield hydrogen ions
A base is a compound that dissolves in water to yield hydroxide ions
Bronsted-Lowery Theory
- An acid is a substance that donates a proton to another substance
- A base is a substance that accepts a proton from another substance
Lewis Theory
- An acid is a substance that can accept a pair of electrons from a base to form a dative covalent bond
- A base is a substance that can donate a pair of electrons to an acid to form a dative bond
Strong acid/base
Ionizes completely in aqueous solutions
Weak acid/base
Ionizes partially in aqueous solutions
Degree of ionisation, α
amount of molecules which ionised at equilibrium/
amount of molecules present initially
pH
pH = -lg [H+]
[H+] = 10^-pH
pOH
pOH = -lg [OH-]
[OH-] = 10^-pOH
Ionic product of water, Kw
Kw = [H+][OH-]
Kw at 25°C = 1.00 *10^-4 mol^2 dm^-6
Relationship between p Kw, pH, pOH
p Kw = pH + pOH (=14 at 25°C)
Acid dissociation constant, Ka
Ka = [H+][A-]/[HA]
p Ka
-lg Ka
Base dissociation constant, Kb
Kb = [BH+][OH-]/[B]
p Kb
-lg Kb
Conjugate acid-base pair
An acid and a base differing by the presence or absence of a proton
Relationship between Ka, Kb and Kw
Ka*Kb = Kw = 1.00 *10^-4 mol^2 dm^-6 (at 25°C)
p Ka + p Kb = p Kw (= 14 at 25°C)
pH of salt of strong acid + strong base
7 (neutral)
pH of salt of weak acid + strong base
> 7 (basic)
pH of salt of strong acid + weak base
<7 (acidic)
pH of salt of weak acid + weak base
depends on Ka and Kb of resulting conjugate acid/base
Buffer solution
A buffer solution is one that can resist a change in pH when a small amount of acid/base is added to it
Acidic buffer solution
A solution with a weak acid and its conjugate base
Basic buffer solution
A solution with a weak base and its conjugate acid
Henderson-Hasselbalch Equation
pH= p Ka + lg ([A-]/[HA])
pOH= p Kb + lg ([BH+]/[B])
