A farmer finds that the crop yield in his field is poor and suspects soil acidity is the problem. Name two substances he could add to the soil to improve it and explain the chemical basis of their action.
Generated by claude-sonnet-4-6 · 2026-06-26 01:03 · grounding rag
Model Answer
Two substances the farmer can add are quicklime (CaO) or slaked lime [Ca(OH)₂].
Chemical basis: Acidic soil has excess H⁺ ions (low pH). Lime being basic produces OH⁻ ions, which neutralise H⁺ ions:
$$\text{H}^+(\text{aq}) + \text{OH}^-(\text{aq}) \rightarrow \text{H}_2\text{O(l)}$$
This raises the soil pH to a suitable level for crop growth.
Source: Chapter 2, Section 2.2
---
Explanation
- The examiner expects you to name two basic substances used to treat acidic soil — quicklime and slaked lime are the standard answers.
- The key concept is neutralisation: acid + base → salt + water. Showing the ionic equation (H⁺ + OH⁻ → H₂O) demonstrates the chemical basis clearly.
- Do not write baking soda here — it is used for acidity in the stomach, not typically for soil in CBSE context. Lime-based answers score full marks.
- 1 mark for naming two substances; 1 mark for the chemical explanation.