Salt
1. What Is a Salt?
In chemistry, a salt is an ionic compound made of:
a cation (positively charged ion, usually from a base)
an anion (negatively charged ion, usually from an acid)
General form: Salt = cation⁺ + anion⁻
Example:
NaCl (sodium chloride)
KNO₃ (potassium nitrate)
CaCO₃ (calcium carbonate)
Salts can be simple or complex, soluble or insoluble, colorless or colored.
2. How Salts Are Formed
A. Neutralization Reaction (most common)
Acid + Base → Salt + Water
Examples:
HCl + NaOH → NaCl + H₂O
H₂SO₄ + KOH → K₂SO₄ + H₂O
B. Metal + Acid
Forms a salt + hydrogen gas.
Example: Zn + 2HCl → ZnCl₂ + H₂
C. Metal Carbonate + Acid
Forms salt + water + CO₂.
Example: CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O
D. Precipitation Reaction
Two soluble salts react to form an insoluble salt.
Example: AgNO₃ + NaCl → AgCl (solid) + NaNO₃
E. Metal Oxide + Acid
Forms salt + water.
Example: CuO + 2HCl → CuCl₂ + H₂O
3. Structure of Salts
Salts are ionic compounds with:
strong electrostatic forces (ionic bonds)
crystalline lattice structure
high melting and boiling points
Example: NaCl forms a cubic crystal lattice.
4. Properties of Salts
A. Physical Properties
Solid at room temperature
Crystalline structure
Hard and brittle
High melting/boiling points
B. Electrical Conductivity
Do NOT conduct electricity as solids
DO conduct when:
melted (molten salt)
dissolved in water Because ions are free to move.
C. Solubility
Some salts are highly soluble, others barely dissolve.
Soluble:
NaCl
KNO₃
Na₂SO₄
Insoluble or low solubility:
AgCl
PbSO₄
CaCO₃
Solubility depends on lattice energy and hydration energy.
5. Types of Salts
A. Neutral Salt
Formed from strong acid + strong base. Example: NaCl
B. Acidic Salt
Has replaceable hydrogen. Example: NaHSO₄
C. Basic Salt
Contains OH⁻ in the structure. Example: Mg(OH)Cl
D. Double Salt
Contains more than one cation/anions but exists only in solid state. Example: Mohr’s salt (FeSO₄·(NH₄)₂SO₄·6H₂O)
E. Complex Salt
Contains a complex ion. Example: K₄[Fe(CN)₆]
6. Hydrated and Anhydrous Salts
Some salts trap water inside their crystal lattice.
Hydrated salts
contain water of crystallization. Example: CuSO₄·5H₂O (blue)
Anhydrous salts
no water molecules. Example: CuSO₄ (white)
Heating a hydrated salt usually drives off water.
7. Uses of Salts
A. Daily life
table salt (NaCl)
baking soda (NaHCO₃)
Epsom salt (MgSO₄)
B. Industry
fertilizers (KNO₃, NH₄NO₃)
explosives (NaNO₃)
glass and ceramics (Na₂CO₃)
metallurgy
pharmaceuticals
8. Important Concepts Related to Salts
A. Lattice Energy
Energy needed to separate ions—higher lattice energy = less soluble.
B. Hydration Enthalpy
Energy released when ions dissolve—higher hydration energy = more soluble.
C. pH of Salt Solutions
Salts can produce acidic, basic, or neutral solutions depending on the strengths of parent acid/base.
Examples:
NaCl → neutral
NH₄Cl → acidic
Na₂CO₃ → basic
9. How Salts Behave in Water
When dissolved:
they dissociate into ions
conduct electricity
may undergo hydrolysis
influence pH
Example: NaCl → Na⁺ + Cl⁻