Question

A 55.33 g KNO3 with molar mass of 101 g/mole was placed in 141g of H2O. with molar mass of 18.0 g/mole. What is the percent by mass of solution?

Answer 1

Molar mass of KNO₃ = 101 g/mol

Mass of KNO₃ = 55.33 g

Moles of KNO₃$(n_1)=$ $\dfrac{55.33}{101}=0.547\space mol$

Molar mass of H₂O = 18 g/mol

Mass of H₂O = 141 g

Moles of H₂O$(n_2)=\dfrac{18}{141}=0.127\space mol$

Mole fraction of KNO₃ $=\dfrac{n_1}{n_1+n_2}=0.81$

Mole fraction of H₂O $=0.19$

Total mass of solution = 196.33 g

Average Molecular mass of solution$(M_{av})=\sum M_i x_i=0.81\times 101+0.19\times18$

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Percent by weight = $\dfrac{85.23}{196.33}\times 100=43.41\%$