Write chemical formula of washing soda. How is it obtained from baking soda? List two uses of washing soda.
Generated by claude-sonnet-4-6 · 2026-06-15 06:45 · grounding rag
Model Answer
Chemical formula of washing soda: Na₂CO₃.10H₂O
Preparation from baking soda:
Baking soda (NaHCO₃) is heated to obtain sodium carbonate (Na₂CO₃). Recrystallisation of sodium carbonate gives washing soda.
$$2\text{NaHCO}_3 \xrightarrow{\Delta} \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2$$
$$\text{Na}_2\text{CO}_3 + 10\text{H}_2\text{O} \rightarrow \text{Na}_2\text{CO}_3.10\text{H}_2\text{O}$$
Two uses of washing soda:
- It is used in glass, soap and paper industries.
- It is used for removing permanent hardness of water.
Source: Chapter 2, Section 2.4.3
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Explanation
- The examiner expects the formula with water of crystallisation (10H₂O) — writing just Na₂CO₃ loses a mark.
- Both steps must be shown: heating NaHCO₃ → Na₂CO₃, then recrystallisation → washing soda. Equations add scoring value.
- For uses, pick any two from the textbook list. "Cleaning agent" and "removing hardness of water" are the most commonly expected answers.