At 40°C Kw is
Correct answer: C. 3.8×10⁻¹⁴
- A. 1.0×10⁻¹⁴
- B. 2.8×10⁻¹⁴
- C. 3.8×10⁻¹⁴
- D. 1.8×10⁻¹⁴
Explanation
The ion product of water (Kw) is temperature-dependent. At 40°C, the correct value of Kw is 3.8×10⁻¹⁴. This increase from the standard 1.0×10⁻¹⁴ at 25°C is due to the endothermic nature of water dissociation, meaning it absorbs heat, which shifts the equilibrium to produce more ions. Therefore, Option C is the only accurate representation of Kw at 40°C. Option A reflects the value at 25°C, Option B is a close estimation but slightly low, and Option D underestimates the effect of temperature increase.
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Acid and base behaviour is explained through the Bronsted-Lowry transfer of protons and the Lewis donation or acceptance of electron pairs. The topic includes pH, pOH, ionisation and water equilibrium, plus salt formation and hydrolysis, where a salt solution may become acidic, basic or neutral.
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