Question

Question #7bb32

Answer 1

`"26% v/v"`

Explanation:

The thing to keep in mind about a solution's volume by volume percent concentration, `"v/v %"`, is that is will always tell you the volume of solute present in `"100 mL"` of solution.

So in order to find a solution's volume by volume percent concentration, all you need to do is to figure out how many milliliters of solute are present for every `"100 mL"` of solution.

In this case, you know that the total volume of the solution is equal to

`overbrace("45 mL ethanol")^(color(blue)("volume of solute")) + overbrace("125 mL water")^(color(blue)("volume of solvent")) = overbrace("170 mL solution")^(color(blue)("volume of solution"))`

You know that this solution contains `"45 mL"` of solute in `"170 mL"` of solution, so you can say that `"100 mL"` of solution will contain

`100 color(red)(cancel(color(black)("mL solution"))) * "45 mL ethanol"/(170color(red)(cancel(color(black)("mL solution")))) = "26.47 mL ethanol"`

Therefore, you can say that this solution is

`color(darkgreen)(ul(color(black)("% v/v = 26% ethanol")))`

The answer must be rounded to two sig figs, the number of sig figs you have for your values.