Define : Common ion effect.(ii) Write preparation of glucose from starch.

Answer:

(i) Common ion effect: The decrease in the degree of dissociation of a weak electrolyte caused by adding a strong electrolyte that has an ion in common with it is called the common ion effect. Example: adding sodium acetate (common ion CH₃COO⁻) to acetic acid suppresses the dissociation CH₃COOH ⇌ CH₃COO⁻ + H⁺.

(ii) Glucose from starch: Starch is hydrolysed by boiling with dilute H₂SO₄ (or dilute HCl) at about 393 K under 2–3 atm pressure:

(C₆H₁₀O₅)_n (starch) + n H₂O —(dil. H₂SO₄, 393 K, 2–3 atm)→ n C₆H₁₂O₆ (glucose)

This is the commercial method of making glucose.