How Anhydrous Differs from Washing Soda in Properties and Uses

The key difference is the presence of water of hydration. Both are forms of sodium carbonate, but their physical properties and, consequently, their primary uses, are distinct.

Anhydrous Sodium Carbonate (Soda Ash)

• Chemical Formula: Na₂CO₃
• Description: A dry, white, powdered or granular solid. "Anhydrous" means "without water."
• Potency: This is the pure, concentrated form (100% Na₂CO₃ by weight).
• Properties: Highly hygroscopic (absorbs moisture from air). It is more chemically reactive by weight due to its concentration.
• Primary Uses: Predominantly industrial. Used in glassmaking, chemical manufacturing, detergents, and metallurgy where purity, concentration, and lack of water are essential.

Washing Soda (Sodium Carbonate Decahydrate)

• Chemical Formula: Na₂CO₃·10H₂O
• Description: A translucent, crystalline solid. The "decahydrate" means each molecule of sodium carbonate is bound to ten molecules of water.
• Potency: This form is much less concentrated. By weight, it is only about 37% Na₂CO₃ (the rest is water).
• Properties: It is efflorescent, meaning it will lose its water of hydration to the air and crumble into a white powder if left exposed (the opposite of hygroscopic). It is generally sold in a crystalline form that dissolves readily in water.
• Primary Uses: Predominantly domestic and commercial. Sold as a laundry booster, water softener, and general-purpose household cleaner. Its crystalline, easy-to-dissolve nature makes it suitable for household use.