pH 0–6.9: acidic. pH 7: neutral (pure water). pH 7.1–14: basic/alkaline. Each whole number change = 10× difference in concentration. pH 4 is 10× more acidic than pH 5.
The 6 strong acids — memorize them, everything else is weak
Hydrochloric, Hydrobromic, Hydroiodic, Nitric, Sulfuric, Perchloric. These fully dissociate in water. Everything else is a weak acid (partial dissociation). If it's not on this list, it's weak.
⚗️ Acids & Bases
Bronsted-Lowry: acid gives H⁺, base takes H⁺
Bronsted-Lowry Definition
The most useful acid-base definition for general chemistry
An acid is a proton (H⁺) donor. A base is a proton acceptor. Every acid-base reaction involves proton transfer. This is broader than the Arrhenius definition and applies to non-aqueous reactions.
⚗️ Acids & Bases
Buffer = weak acid + its conjugate base
Buffer Composition
Buffers resist pH change — always a weak acid/base pair
A buffer contains a weak acid and its conjugate base (or weak base and conjugate acid). They absorb added H⁺ or OH⁻. Blood (pH 7.4) is buffered by the bicarbonate/carbonic acid system.
⚗️ Acids & Bases
Equivalence point = moles acid = moles base
Titration Endpoint
The equivalence point — where titration is complete
At the equivalence point, moles of acid exactly equals moles of base (for 1:1 reactions). Use M₁V₁ = M₂V₂ to find unknown concentration. The endpoint is when the indicator changes color.
pH decreases by 1 for every 10× increase in [H⁺]. pH 3 is 10× more acidic than pH 4. pH + pOH = 14 at 25°C. [H⁺][OH⁻] = 10⁻¹⁴ (Kw). Strong acid HCl 0.1 M → [H⁺] = 0.1 M → pH = 1.
Every acid has a conjugate base, every base has a conjugate acid
HCl donates H⁺ → conjugate base Cl⁻. NH₃ accepts H⁺ → conjugate acid NH₄⁺. Strong acid has weak conjugate base. Weak acid has strong conjugate base. This is why acetate (CH₃COO⁻) is a decent base — it's the conjugate base of a weak acid.
Neutralization Reactions
Neutralization: acid + base → salt + water. HCl + NaOH → NaCl + H₂O
Neutralization Reactions
Acids and bases cancel each other out
Strong acid + strong base → neutral salt (pH 7). Weak acid + strong base → basic salt solution (pH > 7). Strong acid + weak base → acidic salt solution (pH < 7). The net ionic equation for strong acid + strong base: H⁺ + OH⁻ → H₂O.
The equation that predicts buffer pH without a full ICE table
pH = pKa + log([conjugate base]/[weak acid]). When [A⁻] = [HA]: pH = pKa (half-equivalence point). Buffer works best within 1 pH unit of the pKa. Used by biochemists to prepare solutions and by the body to maintain blood pH at 7.35-7.45.
Lewis Acid-Base Theory
Lewis acid = electron pair acceptor. Lewis base = electron pair donor.
Lewis Acid-Base Theory
The broadest definition of acids and bases — no H⁺ required
Extends acid-base chemistry beyond proton transfer. Lewis acid: accepts electron pair (BF₃, metal ions, H⁺). Lewis base: donates electron pair (NH₃, H₂O, F⁻). Explains reactions in non-aqueous systems and coordination chemistry.
Acid-Base Titration
Titration: slowly add known concentration until indicator changes color at equivalence point
Acid-Base Titration
How to find the concentration of an unknown acid or base
Add standard solution (known concentration) to unknown until neutralization. Indicator (phenolphthalein: colorless→pink at pH ~8.2) signals equivalence point. At equivalence point: moles acid = moles base. Calculate: M₁V₁ = M₂V₂ for strong acid-strong base.