Acids, Bases and Salts
Arrhenius definition of acids and bases:
Acid: a chemical compound that increases the concentration of hydrogen ions (H+) in
aqueous solution
Base: a substance that increases the concentration of hydroxide ions (OH -) in
aqueous solution
Brønsted- Lowry definition of acids and bases:
Acid: a molecule or an ion that is a proton donor
Base: a molecule or an ion that is a proton acceptor
Lewis definition of acids and bases:
Acid: atom, ion or molecule that accepts an electron pair to form a covalent bond
Base: atom, ion or molecule that donates an electron pair to form a covalent bond
Properties of Acids
 substances that produces hydrogen ions (H+) in solution - combine with
water and become hydronium ions (H3O+)
Acids:
HCl + H2O  H3O+ + Cl



taste sour
are electrolytes
are corrosive
react w/ indicators to produce a color change
indicator – organic compound that changes color in an acid or base (phenolphthalein)
Common acids –
4 most important industrial acids:
1.
sulfuric acid – car batteries, fertilizers
2. phosphoric acid – detergents, fertilizers
3. nitric acid – fertilizers, explosives (TNT = trinitrotoluene)
4. hydrochloric acid (muriatic acid)- cleaner, gastric juices
Properties of Bases
 substance that produces hydroxide ions (OH-) in solution
Bases:
NaOH + H2O → Na+ + OH




feel slippery
taste bitter
are electrolytes
are corrosive
react w/ indicators to produce a color change

Common bases –
1. ammonia (NH3) – most widely used – cleaners, fertilizers, rayon/nylon production
NH3 + H2O → NH4+ + OH- → NH4OH
2. calcium hydroxide – “caustic lime” used to make mortar and plaster
3. sodium hydroxide “lye” used to make soap, drain cleaner
Strength of acids and bases:
Strong Acid: acid that ionizes almost completely in solution (electrolytes)
HCl(g) + H2O(l) → H3O+(aq) + Cl-
(aq)
Weak Acid: acid that partially ionizes in solution (weak -non electrolytes)
CH3COOH(l) + H2O(l) ↔ H3O+(aq) + Cl-
(aq)
Strong Base: dissociates completely in solution (alkaline)
NaOH + H2O(l) → Na+(aq) + OH-(aq)
Weak Base: partly dissociates in solution
NH3(g) + H2O(l) ↔ NH4+(aq) + OH-
(aq)
Strength
Strong
Acid
HCl, H2SO4, HNO3
Weak
CH3COOH, H2CO3, H3BO3
Base
NaOH, KOH, LiOH, Ca(OH)2,
Ba(OH)2
NH3, Al(OH)3, Fe(OH)3
pH = measure of the concentration of hydronium ions in solution
pH < 7 = acid
pH = 7 = neutral
pH > 7 = base
Neutralization reactions: chemical reaction between an acid and a base.
(produces water and a salt)
H3O+ + OH-  2H2O
Salt: compound formed when the negative ion from an acid combine with positive ions from a
base (any ionic formula).
HCl(g) + NaOH(aq)  H3O+(aq) + Na+(aq) + Cl-(aq) + OH-(aq)
Water formation: H3O+ + OH-(aq)  2H2O
Salt formation: Na+ + Cl-  NaCl
Common Salts:
Sodium chloride (NaCl): table salt
Sodium bicarbonate (NaHCO3): baking soda
Calcium carbonate (CaCO3): calcite/chalk
Potassium nitrate (KNO3): saltpeter
Titration: process in which a solution of known concentration is used to determine the
concentration of another solution
Known concentration: standard: added to unknown with indicator
Endpoint: when one drop of standard causes a color change; usually pink (phenolphthalein
used)