WAEC Chemistry 2025 Theory — Question 66

Model answer

(a) C + distilled water + litmus: dissolves to give a blue solution, turns blue litmus red -> transition metal salt/Cu2+ present, solution is acidic. (b)(i) First portion + NaOH drops then excess: blue precipitate forms, dissolves in excess -> Cu2+ present. (ii) Second portion + NH3 drops then excess: light/pale blue precipitate forms, dissolves in excess to give a deep blue solution -> Cu2+ present. (iii) Third portion + BaCl2 then dilute HCl: white precipitate forms, insoluble in HCl -> SO4^2- present. (iv) Fourth portion + Fehling's solution, boil: brick red/orange precipitate forms -> reducing sugar/glucose present.