Question

A solution containing 66 gram of acetone and 46 gram of water has a density of 1.926 gram/cc. Calculate the molarity of water in the solution.

Answer 1

Mass of solute, acetone = 66g
Molar mass of acetone = 58 g/mol

Moles of acetone = $\frac{\mathrm{Mass}\mathrm{of}\mathrm{solute}}{\mathrm{Molar}\mathrm{mass}\mathrm{of}\mathrm{solute}}=\frac{66}{58}=1.137\mathrm{mol}$

Mass of solvent, water = 46 g
Mass of solution = Mass of (solute + solvent) = 66 + 46 = 112 g
​Density of solution = 1.926 g/cc

Volume of solution = $\frac{\mathrm{Mass}\mathrm{of}\mathrm{solution}}{\mathrm{Density}\mathrm{of}\mathrm{solution}}=\frac{112}{1.926}=58.15\mathrm{cc}\mathrm{or}0.05815\mathrm{L}$

Molarity of solution = $\frac{\mathrm{Moles}\mathrm{of}\mathrm{solute}}{\mathrm{Volume}\mathrm{of}\mathrm{solution}(\mathrm{in}\mathrm{L})}=\frac{1.137}{0.05815}=19.56\mathrm{M}$