# Question 7bb32

Jul 18, 2017

$\text{26% v/v}$

#### Explanation:

The thing to keep in mind about a solution's volume by volume percent concentration, $\text{v/v %}$, is that is will always tell you the volume of solute present in $\text{100 mL}$ 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 $\text{100 mL}$ 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 $\text{45 mL}$ of solute in $\text{170 mL}$ of solution, so you can say that $\text{100 mL}$ 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

$\textcolor{\mathrm{da} r k g r e e n}{\underline{\textcolor{b l a c k}{\text{% v/v = 26% ethanol}}}}$

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