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NCERT Class XII Chemistry
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Question : 5 of 53
Marks: +1, -0
A solution of glucose in water is labelled as 10% w/w. What would be the molality and mole fraction of each component in the solution? If the density of the solution is 1.2 g mL−1^{-1}, then what shall be the molarity of the solution?
Solution:  
Let mass of solution = 100 g
∴ Mass of glucose = 10 g
Mass of water = 90 g = 0.09 kg
No. of moles in 10 g glucose =10180= \frac{10}{180} = 0.0555 mol
No. of moles in 90g H2O\mathrm{H_2O} =9018= \frac{90}{18} = 5 moles
Volume of solution =100 g1.2 gmL−1= \frac{100\,\text{g}}{1.2\,\text{gmL}^{-1}} = 83.33 mL = 0.0833 L
(a) Molality =Number of moles of soluteMass of solvent in kg= \frac{\text{Number of moles of solute}}{\text{Mass of solvent in kg}} =0.0555 mol0.09 kg= \frac{0.0555\,\text{mol}}{0.09\,\text{kg}} = 0.617 m
(b) x (Glucose) =Number of moles of soluteNumber of moles of solution= \frac{\text{Number of moles of solute}}{\text{Number of moles of solution}} =0.05555.0555= \frac{0.0555}{5.0555} = 0.01
∴ x (H2O)(\mathrm{H_2O}) = 1 – 0.01 = 0.99
(c) Molarity =Number of moles of soluteVolume of solution in L= \frac{\text{Number of moles of solute}}{\text{Volume of solution in L}} =0.05550.0833= \frac{0.0555}{0.0833} = 0.666 M
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