Question

The chemical formula of washing soda is :

• A. \(Na_2CO_3 \cdot 10H_2O\)
• B. \(NaHCO_3\)
• C. \(CH_3COONa\)
• D. \(Na_2CO_3\)

Hint:

Distinguish between the two forms of sodium carbonate:
- \(Na_2CO_3\) = Soda Ash (Anhydrous, no water).
- \(Na_2CO_3 \cdot 10H_2O\) = Washing Soda (Decahydrate, has 10 water molecules).

Answer 1

The Correct Option is A

Step 1: Name the compound behind washing soda.
Washing soda is the crystallised, hydrated form of sodium carbonate, made through the Solvay process.
Step 2: Count its water molecules.
When sodium carbonate crystallises out of solution, it locks in ten water molecules per formula unit, giving \[ Na_2CO_3 \cdot 10H_2O \]
Step 3: Eliminate the look alike options.
$NaHCO_3$ is baking soda, a different compound entirely. $CH_3COONa$ is sodium acetate, the salt of vinegar's acid. Plain $Na_2CO_3$ without any water attached is soda ash, the anhydrous starting material, not washing soda itself.
Step 4: Conclude.
Washing soda's formula is $Na_2CO_3 \cdot 10H_2O$. \[ \boxed{Na_2CO_3 \cdot 10H_2O} \]