Acids and Bases

Acid: A substance that increases the concentration of H⁺ ions in solution when it dissolves. Alternatively, a proton (H⁺) donor. Note that H⁺_(aq) = H₃O⁺_(aq).
Base: A substance that increases the concentration of OH^- ions in solution when it dissolves. Alternatively, a proton (H⁺) acceptor. For example, be able to identify (label) acids and bases in any acid/base reaction.

CH₃CO₂H	+	NH₃	→	CH₃CO₂^-	+	NH₄⁺
H⁺ donor		H⁺ acceptor		H⁺ acceptor		H⁺ donor
acid		base		base		acid

Dissociation: The splitting apart of an acid into H⁺ and an anion. For example: H₂SO₄ H⁺ + HSO₄^-.
Acid Dissociation constant (K_a): Measure of acid strength. Large values indicate stronger acids. For the reaction given above:
K_a = ([H⁺] [A^-]) / [HA] = ([H⁺] [HSO₄^-]) / [H₂SO₄]
Ion-Product Constant for Water: K_w = [H⁺] [OH^-] = 1.00 x 10^-14

pH:

Measure of acid/base strength. pH = 7 is neutral. pH < 7 is acidic. pH > 7 is basic.

pH = -log₁₀ ( [H⁺] )

Buffers:

A buffer solution is a mixture of a weak acid and its conjugate base. Buffers are important because they prevent drastic pH changes from occurring. The pH of a buffer solution can be calculated using the Henderson-Hasselbalch equation:

pH = pK_a + log₁₀ ([A^-] / [HA])
where
pK_a = -log₁₀ ( K_a )

Calculator Hints:

Calculate pH given [H⁺] = 3.4 x 10+] = 3.4 x 10^-5. Use pH = -log(3.4x10^-5)

[3] [.] [4] [EE] [5] [+/-] [=] [log] [+/-]

(Answer should be +4.4685 = 4.47)

Calculate [H⁺] given pH = 4.30. Use pH = -log(H⁺)

[4] [.] [3] [0] [+/-] [EE] [=] [INV] [log]

(Answer should be +5.0119 x 10^-5 = 5.01 x 10^-5)