The Chemistry of Acids and Bases

Acid

Substance donating hydrogen ions (H+) in water.

Base

Substance donating hydroxide ions (OH-) in water.

Arrhenius Definition

Acid/base theory focusing on H+ and OH- ions.

Bronsted-Lowry Definition

Acid donates protons; base accepts protons.

Lewis Definition

Acid accepts electron pairs; base donates electron pairs.

Conjugate Acid-Base Pair

Compounds differing by one hydrogen ion.

Hydronium Ion

H3O+; indicates an acidic solution.

Hydroxide Ion

OH-; indicates a basic solution.

Monoprotic Acid

Acid donating one proton (e.g., HC₂H₃O₂).

Diprotic Acid

Acid donating two protons (e.g., H₂C₂O₄).

Polyprotic Acid

Acid donating multiple protons (e.g., H₃PO₄).

Amphiprotic

Substance acting as either acid or base.

Acid Dissociation Reaction

Reaction showing acid ionization in water.

Conjugate Base

Base formed when an acid donates a proton.

Conjugate Acid

Acid formed when a base accepts a proton.

Weak Acid

Partially ionizes in solution; equilibrium established.

Strong Acid

Completely ionizes in solution; no equilibrium.

Buffer System

Resists changes in pH; utilizes conjugate pairs.

Sulfuric Acid

Economic indicator; strong diprotic acid.

Ammonia

Major exception in acid-base theories; acts as base.

Coordinate Covalent Bond

Bond formed when one atom donates both electrons.

Ionization Reaction

Process of an acid or base dissociating in solution.

Alkaline Solution

Solution with excess hydroxide ions (OH-).

Acidic Solution

Solution with excess hydronium ions (H3O+).

pH Scale

Measures acidity or basicity; ranges from 0 to 14.

Neutral Compound

Substance with equal concentrations of H+ and OH-.

Hydrated Aluminum Ion

[Al(H₂O)₆]³⁺ complex in solution.

Dissociation

Process where compounds separate into ions.

Strong Acid

Completely dissociates in water, large K value.

Weak Acid

Partially dissociates in water, small K value.

Hydrochloric Acid

Strong acid, formula HCl, fully dissociates.

Nitric Acid

Strong acid, formula HNO₃, fully dissociates.

Sulfuric Acid

Strong acid, formula H₂SO₄, fully dissociates.

Perchloric Acid

Strong acid, formula HClO₄, fully dissociates.

Bond Strength

Energy required to break a bond, measured in kJ/mol.

Hydrogen Halides

Group of strong acids including HCl, HBr, HI.

Oxyacid

Acids containing oxygen, strength increases with more oxygen.

Acid Dissociation Constant (Ka)

Equilibrium constant for acid dissociation reactions.

Conjugate Base

Species formed when an acid donates a proton.

Equilibrium Position

Location of equilibrium in a dissociation reaction.

Electron Density

Distribution of electrons around atoms in a molecule.

Hydronium Ion

H₃O⁺, formed when acids dissolve in water.

Acid Strength

Determined by the position of dissociation equilibrium.

Strong Base

Completely dissociates in water, includes IA and IIA hydroxides.

Weak Base

Partially dissociates in water, includes organic bases.

Relative Strengths

Comparison of acid/base strength based on dissociation.

Polyatomic Ion

Ion composed of two or more atoms.

Carboxyl Group

Functional group -COOH, found in organic acids.

Acetic Acid

Weak organic acid, formula CH₃COOH.

Benzoic Acid

Weak organic acid, formula C₇H₆O₂.

Hydrogen Sulfate Ion

Anion formed from sulfuric acid, HSO₄⁻.

Ionization

Process of forming ions from neutral molecules.

Equilibrium Expression

Mathematical representation of concentrations at equilibrium.

Chlorous acid

Weak acid with formula HClO₂.

Monochloracetic acid

Chlorinated acetic acid, formula C₂HClO₂.

Hydrofluoric acid

Strong acid with formula HF.

Nitrous acid

Weak acid with formula HNO₂.

Acetic acid

Weak acid with formula CH₃COOH.

Hydrated aluminum(III) ion

Aluminum ion in aqueous solution, Al³⁺.

Hypochlorous acid

Weak acid with formula HClO.

Hydrocyanic acid

Weak acid with formula HCN.

Ammonium ion

Positively charged ion, NH₄⁺.

Phenol

Aromatic compound with hydroxyl group, C₆H₅OH.

Methylamine

Weak base with formula CH₃NH₂.

Dimethylamine

Weak base with formula (CH₃)₂NH.

Trimethylamine

Weak base with formula (CH₃)₃N.

Pyridine

Aromatic nitrogen-containing weak base, C₅H₅N.

Equilibrium expression for acids

Ka = [H₃O⁺][A⁻]/[HA].

Equilibrium expression for bases

Kb = [HB⁺][OH⁻]/[B].

Autoionization of water

Water dissociates into H₃O⁺ and OH⁻.

Kw

Autoionization constant of water, 1.008 × 10⁻¹⁴.

Neutral solution

[H⁺] = [OH⁻] = 1.0 × 10⁻⁷ M.

Endothermic reaction

Absorbs heat, shifts equilibrium right.

pH scale

Logarithmic scale measuring hydrogen ion concentration.

Weak bases examples

Includes ammonia, methylamine, ethylamine.

Relative base strength

Rank based on Kb values.

Hydronium ion

H₃O⁺, formed when acids dissociate.

Hydroxide ion

OH⁻, produced by bases in solution.

Conjugate acid

Species formed when a base accepts H⁺.

Conjugate base

Species remaining after an acid donates H⁺.

Strong acid

Completely dissociates in solution.

Weak acid

Partially dissociates in solution.

Weak base

Partially reacts with water to form OH⁻.

pH

Measure of hydrogen ion concentration in solution.

pOH

Measure of hydroxide ion concentration in solution.

pH scale

Ranges from 0 (acidic) to 14 (basic).

Acidic solution

pH less than 7.000.

Neutral solution

pH equal to 7.000.

Basic solution

pH greater than 7.000.

Significant figures in pH

Match decimal places to least accurate measurement.

Logarithmic scale

pH scale based on logarithm of ion concentration.

[H+]

Concentration of hydrogen ions in molarity.

[OH-]

Concentration of hydroxide ions in molarity.

Water dissociation constant

Kw = [H+][OH-] = 1 × 10^-14.

Calculating pH

pH = -log[H+].

Calculating pOH

pOH = -log[OH-].

pH and pOH relationship

pH + pOH = 14 at 25°C.

Strong acid example

pH of 0.10 M HNO3 is 1.00.

Strong base example

pH of 5.0 × 10^2 M NaOH is 12.70.

Weak acid equilibrium

Set up Kₐ expression for weak acids.