A solution of ethanol in water is `10%` by volume. If the solution and pure ethanol have densities of `0.9866 g mL^(-1)` and `0.785 mL^(-1)` respectively, the mass precent will be

Options

A. 0.0957
B. 0.0759
C. 0.0579
D. 7.95%`

Answer

4

Explanation

`10%` by volume means in every `100 ml` of solution there is `10 ml` of ethanol. To get the mass percent we must divide the mass of ethanol by the mass of solution followed by multiplication with `100%`. Use densities to find the mass of ethanol and mass of solution.
According to volume percent `(10%)`, we have
Volume of ethanol `=10 mL`
Volume of solution `=100 mL`
Thus
`"Mass of ethanol" = "volume" xx "density"`
`=(10 mL)(0.785 g mL^(-1))`
`=7.85 g`
`"Mass of solution" = "volume" xx "density"`
`=(100 mL) (0.9866 g)`
`=98.66 g`
Thus,
Mass percent `=("Mass of component")/("Total mass of solution")xx100%`
`=(7.85g)/(98.66 g)xx100%`
`=7.95%`