Question

Question #c25e3

Answer 1

400-86/400 *100

Answer 2

Your solution is `78.5% "v/v"` ethanol.

Explanation:

A solution's percent concentration by volume is defined as the ratio between the volume of the solute, in your case ethanol, and the total volume of the solution, multiplied by 100.

`"%v/v" = "volume of solute"/"volume of solution" xx 100`

In your case, you know that the total volume of the solution is equal to `"400 mL"`. Moreover, you know that this solution contains `"86 mL"` of water, which also implies that it must contain

`V_"solution" = V_"water" + V_"ethanol"`

`V_"ethanol" = V_"solution" - V_"water"`

`V_"ethanol" = "400 mL" - "86 mL" = "314 mL ethanol"`

The percent concentration by volume of ethanol in this solution is

`"%v/v" = (314color(red)(cancel(color(black)("mL"))))/(400color(red)(cancel(color(black)("mL")))) xx 100 = color(green)("78.5%")`

I'll leave the answer rounded to thre sig figs.