When the acid present in tamarind is mixed with a base, a mixture is produced. When the base is mixed into kneaded flour and heated, cakes become soft and spongy. The base is prepared with common salt and is also used for faster cooking.
Generated by claude-sonnet-4-6 · 2026-06-15 06:44 · grounding rag
Model Answer
The clues identify:
- X = Tartaric acid (acid in tamarind) — Chemical formula: C₄H₆O₆
- Y = Baking soda (base mixed into flour) — Common name: Baking soda; Chemical formula: NaHCO₃
- Z = Washing soda (prepared from common salt, used for faster cooking) — Common name: Washing soda; Chemical formula: Na₂CO₃
(i) X = Tartaric acid, C₄H₆O₆; Y = Baking soda, NaHCO₃; Z = Washing soda, Na₂CO₃
(ii) Baking soda (NaHCO₃) is prepared by treating a solution of sodium chloride (brine) with ammonia and CO₂ (Solvay process), or from washing soda and CO₂:
$$\text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2 \rightarrow 2\text{NaHCO}_3$$
On heating, NaHCO₃ releases CO₂ gas:
$$2\text{NaHCO}_3 \xrightarrow{\Delta} \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2\uparrow$$
The CO₂ produced gets trapped in the dough, making the cake soft and spongy.
(iii) Milk of magnesia — Mg(OH)₂ — is a mild base used as an antacid.
Source: Chapter 2, Salts and their uses
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Explanation
- The question is a disguised identification puzzle: tamarind acid = tartaric acid (X), the base added to flour = baking soda (Y), prepared from common salt and used for faster cooking = washing soda (Z).
- Examiners expect all three names + formulae in (i); don't skip any.
- For (ii), the key points are: how NaHCO₃ is made and the decomposition equation showing CO₂ release — both are required for full marks.
- For (iii), Mg(OH)₂ (milk of magnesia) is the standard NCERT answer for a mild base antacid. Do not write NaOH (it is a strong base).