Difference Between Sodium Hydroxide and Aluminum Hydroxide

Main Difference – Sodium Hydroxide vs Aluminum Hydroxide

Sodium hydroxide and aluminum hydroxide are metal hydroxides. The chemical formula of sodium hydroxide is NaOH. The common name for sodium hydroxide is caustic soda. It is an ionic compound. Aluminum hydroxide is an amphoteric hydroxide that has both acidic and basic properties. The chemical formula of aluminum hydroxide is Al(OH)3. The main difference between sodium hydroxide and aluminum hydroxide is that sodium hydroxide is a basic compound whereas aluminum hydroxide is an amphoteric compound.

Key Areas Covered

1. What is Sodium Hydroxide
     – Definition, Chemical Properties, Applications
2. What is Aluminum Hydroxide
     – Definition, Chemical Properties, Applications
3. What is the Difference Between Sodium Hydroxide and Aluminum Hydroxide
     – Comparison of Key Differences

Key Terms: Aluminum Hydroxide (Al(OH)3), Amphoteric, Brønsted-Lowry Base, Caustic Soda, Exothermic, Hygroscopic, Lewis Acid, Sodium Hydroxide (NaOH)

Difference Between Sodium Hydroxide and Aluminum Hydroxide - Comparison Summary

What is Sodium Hydroxide

Sodium hydroxide is a metal hydroxide having the chemical formula NaOH. The common name for sodium hydroxide is caustic soda. Sodium hydroxide is an ionic compound made of sodium cations (Na+) and hydroxide (OH) anions. It is a strong base.

The molar mass of sodium hydroxide is 39.99 g/mol. Sodium hydroxide is a solid at room temperature and appears as white, waxy crystals which are opaque. It is odorless. The melting point of sodium hydroxide is 318 °C and the boiling point is 1,388 °C.

Difference Between Sodium Hydroxide and Aluminum Hydroxide

Figure 1: Sodium Hydroxide Solid Compound

Since sodium hydroxide is a strongly basic compound, it can cause severe burns. It is highly water-soluble. When dissolved in water, this ionic compound dissociates into its ions. This dissolution in water is highly exothermic. Sodium hydroxide is hygroscopic. This means, sodium hydroxide can absorb water vapor and carbon dioxide from the air when exposed to normal air.

The applications of sodium hydroxide include its use in the manufacturing of many soaps and detergents, manufacture of medicine such as aspirin, controlling water acidity, dissolving unwanted material in the wood when producing wood and paper products, etc.

What is Aluminum Hydroxide

Aluminum hydroxide is an amphoteric hydroxide having the chemical formula Al(OH)3. Amphoteric means this compound shows both acidic and basic properties. Aluminum hydroxide is found in nature as the mineral known as gibbsite.

The molar mass of aluminum hydroxide is 78 g/mol. The melting point is 300 °C. Aluminum hydroxide appears as an amorphous white powder. When aluminum hydroxide is reacted with an acid, it acts as a Brønsted-Lowry base and accepts protons. When reacted with bases, it acts as a Lewis acid by accepting an electron pair from a hydroxyl anion.  

Main Difference - Sodium Hydroxide vs Aluminum Hydroxide

Figure 2: Aluminum Hydroxide Chemical Structure

The uses of aluminum hydroxide include:

  • feedstock for the production of other aluminum compounds
  • a fire retardant filler for polymer applications
  • an antacid in humans and animals, etc.

Difference Between Sodium Hydroxide and Aluminum Hydroxide

Definition

Sodium Hydroxide: Sodium hydroxide is a metal hydroxide having the chemical formula NaOH.

Aluminum Hydroxide: Aluminum hydroxide is an amphoteric hydroxide having the chemical formula Al(OH)3.

Hydroxide Anions

Sodium Hydroxide: There is one hydroxide anion per one sodium cation in sodium hydroxide.

Aluminum Hydroxide: There are three hydroxide anions per one aluminum cation in aluminum hydroxide.

Nature

Sodium Hydroxide: Sodium hydroxide is a basic compound.

Aluminum Hydroxide: Aluminum hydroxide is an amphoteric compound.

Molar Mass

Sodium Hydroxide: The molar mass of sodium hydroxide is 39.99 g/mol.

Aluminum Hydroxide: The molar mass of aluminum hydroxide is 78 g/mol.

Melting Point

Sodium Hydroxide: The melting point of sodium hydroxide is 318 °C

Aluminum Hydroxide: The melting point of aluminum hydroxide is 300 °C.

Reaction with Acids

Sodium Hydroxide: Sodium hydroxide reacts with acids, forming a sodium salt.

Aluminum Hydroxide: When aluminum hydroxide reacts with an acid, it acts as a Brønsted-Lowry base and accept protons.

Reaction with Bases

Sodium Hydroxide: Sodium hydroxide does not react with bases.

Aluminum Hydroxide: When reacted with bases, it acts as a Lewis acid by accepting an electron pair from a hydroxyl anion. 

Conclusion

Both sodium hydroxide and aluminum hydroxide are ionic compounds consist of metal cations and hydroxide anions. The main difference between sodium hydroxide and aluminum hydroxide is that sodium hydroxide is a basic compound whereas aluminum hydroxide is an amphoteric compound.

Reference:

1. “SODIUM HYDROXIDE.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, Available here.

Image Courtesy:

1. “Sodium hydroxide image” By Hari vinayak santhosh – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Aluminium hydroxide” By Copsi (Public Domain) via Commons Wikimedia

About the Author: Madhusha

Madhusha is a BSc (Hons) graduate in the field of Biological Sciences and is currently pursuing for her Masters in Industrial and Environmental Chemistry. Her interest areas for writing and research include Biochemistry and Environmental Chemistry.

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