WAEC Chemistry 2021 Theory — Question 18
Question 18 of 31 from the West African Examinations Council (WAEC) Chemistry 2021 Theory paper, with the correct answer and a full explanation.
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3(c). 25.0cm³ of hydrochloric acid was completely neutralized by 24.0cm³ of 0.150 mol dm⁻³ aqueous KOH using a suitable indicator. (i) Write a balanced chemical equation for the reaction. (ii) Calculate the concentration of the acid.
Model answer
(i) KOH + HCl → KCl + H2O. (ii) Moles of KOH = 0.150 × 24/1000 = 0.0036 mol. Since the mole ratio acid:base = 1:1, moles of HCl = 0.0036 mol. Concentration of HCl = 0.0036 / (25/1000) = 0.144 mol dm⁻³.
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