Aluminum Hydroxide Precipitation

AlCl₃ + 3NaOH → Al(OH)₃↓ + 3NaCl

Overview

Aluminum chloride reacts with sodium hydroxide to form a white gelatinous precipitate of aluminum hydroxide (Ksp = 3 × 10⁻³⁴). Al(OH)₃ is amphoteric: it dissolves in excess NaOH to form aluminate [Al(OH)₄]⁻. The gelatinous precipitate is an excellent flocculating agent.

Participants

Role	Substance	Coefficient	State
Product	Aluminum Hydroxide Al(OH)₃	1	(s)
Product	Sodium Chloride NaCl	3	(aq)

Everyday Example

Water treatment plants use aluminum salts to form Al(OH)₃ flocs that trap suspended particles, clarifying drinking water.

Industrial Importance

Al(OH)₃ coagulation is the most widely used water purification method globally. Aluminum hydroxide is also used as a fire retardant and antacid.

Properties

Type: Precipitation
Reversible: No
Energy: Exothermic
ΔH: -115.0 kJ/mol

Related Reactions

Barium Carbonate Precipitation Barium Sulfate Precipitation Cadmium Sulfide Precipitation (Yellow) Calcium Carbonate Precipitation Calcium Fluoride Precipitation (Fluorite) Calcium Oxalate Precipitation (Kidney Stones) Calcium Phosphate Precipitation (Bone Mineral) Calcium Sulfate Precipitation (Gypsum) Chromium(III) Hydroxide Precipitation Cobalt(II) Hydroxide Precipitation

Frequently Asked Questions

What is the equation for Aluminum Hydroxide Precipitation?

The balanced equation is: AlCl₃ + 3NaOH → Al(OH)₃↓ + 3NaCl.

What type of reaction is Aluminum Hydroxide Precipitation?

Aluminum Hydroxide Precipitation is a precipitation reaction.

Is Aluminum Hydroxide Precipitation exothermic or endothermic?

Aluminum Hydroxide Precipitation is exothermic (releases energy). The enthalpy change (ΔH) is -115.0 kJ/mol.