Bases and Alkalis
Bases are chemical substances that react with acids to form salt and water. They play an essential role in neutralization reactions and are found in many industrial, household, and biological applications.
Definitions of a Base
- Arrhenius Definition: A base is a substance that produces hydroxide ions (OH⁻) when dissolved in water.
$$ \text{NaOH (aq)} \rightarrow \text{Na}^+ (aq) + \text{OH}^- (aq) $$ - Brønsted-Lowry Definition: A base is a substance that accepts protons (H⁺) from an acid.
Example: $$ \text{NH}_3 + \text{H}^+ \rightarrow \text{NH}_4^+ $$ - Lewis Definition: A base is a substance that donates an electron pair to form a covalent bond.
Example: $$ \text{NH}_3 : + \text{BF}_3 \rightarrow \text{F}_3\text{B–NH}_3 $$
Bases and Alkalis
Although the terms are sometimes used interchangeably, there is a difference between a base and an alkali:
- Bases: Are substances that neutralize acids to form salts and water. They may be soluble or insoluble in water.
Example: CuO, ZnO, Fe(OH)₂. - Alkalis: Are soluble bases that release hydroxide ions (OH⁻) in aqueous solution.
Example: NaOH, KOH, Ca(OH)₂.
Bases & Chemical Formula
| Base | Chemical Formula |
|---|---|
| Sodium hydroxide(Caustic soda) | NaOH |
| Potassium hydroxide | KOH |
| Ammonium hydroxide | NH₄OH |
| Calcium hydroxide (slaked lime) | Ca(OH)₂ |
| Magnesium hydroxide(milk of magnesia) | Mg(OH)₂ |
| Copper(II) hydroxide | Cu(OH)₂ |
| Iron(II) hydroxide | Fe(OH)₂ |
| Iron(III) hydroxide | Fe(OH)₃ |
| Zinc hydroxide | Zn(OH)₂ |
| Aluminium hydroxide | Al(OH)₃ |
Strength of a Base
The strength of a base depends on the extent to which it dissociates in water to produce hydroxide ions (OH⁻).
- Strong Bases: Completely ionize in water to produce a high concentration of OH⁻ ions.
Examples: NaOH, KOH, Ca(OH)₂.
$$ \text{NaOH (aq)} \rightarrow \text{Na}^+ + \text{OH}^- $$ - Weak Bases: Partially ionize in water to produce a low concentration of OH⁻ ions.
Examples: NH₄OH, Mg(OH)₂.
$$ \text{NH}_4\text{OH (aq)} \rightleftharpoons \text{NH}_4^+ + \text{OH}^- $$
Precautions in Handling Bases
- Always wear protective gloves, goggles, and a lab coat when handling bases.
- Handle concentrated bases (like NaOH and KOH) with care as they are corrosive and can burn the skin.
- Avoid inhaling fumes from strong bases such as ammonia solution.
- In case of contact with skin, wash immediately with plenty of water.
- Store bases in properly labeled containers away from acids and flammable substances.
- Do not pipette bases by mouth; always use a pipette filler.
- Work in a well-ventilated area when using volatile bases such as NH₄OH.