WAEC Chemistry 2010 Theory — Question 9
Question 9 of 46 from the West African Examinations Council (WAEC) Chemistry 2010 Theory paper, with the correct answer and a full explanation.
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2a(ii) The solubility of KNO3 at 20°C was 3.00 mol dm⁻³. If 67.0 g of KNO3 was added to 250 cm³ of water and stirred at 20°C, determine whether the solution formed was saturated or not at that temperature. [KNO3=101.0]
Model answer
Mass = 67.0g. Molar mass of KNO3 = 101 gmol⁻¹. Mole of KNO3 = 67.0g/101gmol⁻¹ = 0.6634 mol. Volume = 250cm³ = 0.25dm³. Concentration = 0.6634mol/0.25dm³ = 2.6536 moldm⁻³. Since the solubility of KNO3 at 20°C (3 moldm⁻³) is greater than the concentration of the solution formed (2.6536 moldm⁻³), the solution is unsaturated.
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