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Standard XII

Chemistry

Laws of Mass Conservation

1.0 g of a sa...

Question

$1.0$ g of a sample containing $N a C l$ , $K C l$ and some inert impurity is dissolved in excess of water and treated with excess of $A g N O_{3}$ solution. A $2.0$ g precipitate of $A g C l$ separate out also sample is $23 %$ by mass in sodium. Determine the mass percentage of $K C l$ in the sample.

45

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29.28

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10

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52.10

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Solution

The correct option is C $29.28$ %
The mass of sample is $1.0$ g.
The sample is $23$ % by mass in sodium.
The mass of sodium is $\frac{23}{100} \times 1.0 = 0.23$ g
The atomic masses of Na and Cl are 23.0 g/mol and 35.5 g/ mole.
In $N a C l$ , 0.23 g of Na corresponds to $\frac{35.5}{23.0} \times 0.23 = 0.355$ g of chlorine.
The molar mass of $A g C l$ is 143.5 g/mol and the atomic mass of $C l$ is 35.5 g/mol.
A 2.0 g precipitate of $A g C l$ separate out.
2.0 g of $A g C l$ corresponds to $\frac{35.5}{143.5} \times 2.0 = 0.495$ g of chlorine.
Out of 0.495 g of chlorine, 0.355 g of chlorine is from $N a C l$ . The remaining $0.495 - 0.355 = 0.140$ g is from $K C l$ .
The molar mass of $K C l$ is 74.6 g/mol. The atomic mass of chlorine is 35.5 g/mol.
0.140 of chlorine corresponds to $\frac{74.6}{35.5} \times 0.140 = 0.2928$ g of $K C l$ .
The mass of sample is 1.0 g. The mass of $K C l$ is 0.294 g. The mass percent of $K C l$ in sample is $\frac{0.2928}{1.0} \times 100 = 29.28$ %

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1.0 g of a sample containing NaCl, KCl and some inert impurity is dissolved in excess of water and treated with excess of AgNO3 solution. A 2.0 g precipitate of AgCl separate out also sample is 23% by mass in sodium. Determine the mass percentage of KCl in the sample.