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ICSE Class 10 Chemistry Question 13 of 28

Stoichiometry — Percentage Composition — Empirical & Molecular Formula — Chemical Equations — Question 21

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21
Question

Question 1(2009)

Commercial NaOH weighing 30 g. has some NaCl in it. The mixture on dissolving in water and treatment with excess AgNO3 soln. formed a precipitate weighing 14.3 g. What is the percentage of NaCl in the commercial sample of NaOH.

NaCl + AgNO3 ⟶ AgCl + NaNO3

[Relative molecular mass of NaCl = 58 ; AgCl = 143]

Answer

NaCl58g+AgNO3⟶AgCl143 g+NaNO3\underset{58 \text{g}}{\text{NaCl}} + \text{AgNO}_3 \longrightarrow \underset{143 \text{ g}}{\text{AgCl}} + \text{NaNO}_3

(i) 143 g AgCl is formed by 58 g NaCl

∴ 14.3 g of AgCl will be formed by 58143\dfrac{58}{143} x 14.3 = 5.8 g

Percentage of NaCl = 5.830\dfrac{5.8}{30} x 100 = 19.33%

Hence, percentage of NaCl is 19.33%