Q.Which of the following is the molecular formula of washing soda ?

Sodium Carbonate and Bicarbonate: The Two Faces of Soda

Think of a family where two siblings share the same basic nature but behave very differently. Sodium carbonate ($\text{Na}_2\text{CO}_3$) and sodium bicarbonate ($\text{NaHCO}_3$) are exactly that — close chemical relatives with one crucial difference: bicarbonate carries an extra hydrogen atom.

The Intuition: One Extra Proton Changes Everything

Both are salts of carbonic acid ($\text{H}_2\text{CO}_3$), a weak acid that forms when carbon dioxide dissolves in water. Carbonic acid has two hydrogen atoms it can lose. When it loses both hydrogens, you get the carbonate ion ($\text{CO}_3^{2-}$). When it loses only one, you get the bicarbonate ion ($\text{HCO}_3^-$).

This single hydrogen makes bicarbonate less alkaline and more reactive to heat and acids than carbonate.

The Precise Chemistry

Sodium Carbonate — $\text{Na}_2\text{CO}_3$ (washing soda)

• A white, odourless powder that dissolves in water to give a strongly alkaline solution (pH ~11).
• It does not decompose on heating — it's thermally stable up to its melting point (851°C).
• Made industrially by the Solvay process: ammonia, brine (NaCl), and limestone (CaCO₃) react in a cycle to produce $\text{Na}_2\text{CO}_3$.

Sodium Bicarbonate — $\text{NaHCO}_3$ (baking soda)

• A white crystalline powder that gives a mildly alkaline solution (pH ~8.3).
• Decomposes on heating above 50°C, releasing carbon dioxide gas:

• This CO₂ release is what makes baking soda puff up dough — the gas bubbles get trapped, giving cakes and bread their spongy texture.

Key Differences at a Glance

Why This Matters for Exams …