Baking soda and washing soda are both manufactured starting from sodium chloride, yet they serve very different purposes. (i) Trace the sequence of industrial/chemical steps (Solvay process and beyond) that connect NaCl to each of these two products. (ii) For each product, explain one specific use that depends directly on its chemical nature — acidic, basic, or otherwise. (iii) How are baking soda and washing soda chemically related to each other?
Generated by claude-sonnet-4-6 · 2026-06-26 01:06 · grounding rag
Model Answer
(i) Steps from NaCl to each product:
Baking soda (NaHCO₃): NaCl is treated with water, CO₂, and NH₃ (Solvay-type reaction):
$$\text{NaCl} + \text{H}_2\text{O} + \text{CO}_2 + \text{NH}_3 \rightarrow \text{NH}_4\text{Cl} + \text{NaHCO}_3$$
Washing soda (Na₂CO₃·10H₂O): Baking soda is heated to give Na₂CO₃, which is then recrystallised with water:
$$2\text{NaHCO}_3 \xrightarrow{\Delta} \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2$$
$$\text{Na}_2\text{CO}_3 + 10\text{H}_2\text{O} \rightarrow \text{Na}_2\text{CO}_3.10\text{H}_2\text{O}$$
(ii) Uses linked to chemical nature:
- Baking soda is a mild non-corrosive base (NaHCO₃). Being alkaline, it neutralises excess acid in the stomach, making it effective as an antacid.
- Washing soda is a basic salt. It removes permanent hardness of water by reacting with dissolved calcium/magnesium salts.
(iii) Chemical relationship:
Baking soda (NaHCO₃) and washing soda (Na₂CO₃·10H₂O) are chemically related — washing soda is produced from baking soda itself. Heating NaHCO₃ gives Na₂CO₃, which on recrystallisation becomes washing soda. Both are sodium salts of carbonic acid; baking soda has one Na⁺ (acid salt) while washing soda has two Na⁺ (normal salt).
Source: Chapter 2, Section 2.4.3
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Explanation
- Examiners expect the equations for both products — write them clearly for full marks.
- For part (ii), always link the use to the chemical property (basic nature → neutralises acid; basic salt → softens water). Don't just list uses.
- For part (iii), the key point is that washing soda is made from baking soda, and both are sodium carbonate salts differing in the number of Na⁺ ions and water of crystallisation. This shows their direct chemical relationship.
- Keep equations balanced; the heating arrow (Δ) over the arrow is expected.