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2022 O Level Chem P1 Q12 — Stoichiometry / Reacting Masses Solution

Stoichiometry / Reacting Masses 2022 O Level Pure Chemistry · Paper 1 · Q12

Question

Aqueous sodium chloride and aqueous silver nitrate react according to the equation shown. NaCl(aq) + AgNO₃(aq) → AgCl(s) + NaNO₃(aq). No other reactions occur in the solution. A mixture of solid sodium chloride and solid sodium nitrate is analysed. 0.060 g of this mixture is dissolved in water. It is reacted with 0.02 mol/dm³ aqueous silver nitrate, using a suitable indicator to show when the reaction is complete. The volume of aqueous silver nitrate required is 29.4 cm³. What is the percentage by mass of sodium chloride in the mixture?

A42.7%
B57.3%
C58.8%
D83.3%

Correct answer: B

Video Solution

Explanation

Answer: B. Only the NaCl in the mixture reacts with \(\text{AgNO}_3\); the \(\text{NaNO}_3\) is inert here.

Moles of \(\text{AgNO}_3\) used \(= 0.02 \times \dfrac{29.4}{1000} = 5.88 \times 10^{-4}\) mol. Mole ratio \(\text{NaCl} : \text{AgNO}_3 = 1 : 1\), so moles of NaCl in the mixture \(= 5.88 \times 10^{-4}\) mol.

\(M_r(\text{NaCl}) = 23 + 35.5 = 58.5\). Mass of NaCl \(= 5.88 \times 10^{-4} \times 58.5 = 0.0344\) g.

Percentage by mass of NaCl in the mixture \(= \dfrac{0.0344}{0.060} \times 100 \approx 57.3\%\) — option B.

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