# Question a4ff2

Apr 5, 2016

$\text{39 mL}$

#### Explanation:

Your stock solution is $\text{32% v/v}$ isopropyl alcohol, which is commonly called rubbing alcohol, which means that every $\text{100 mL}$ of this stock solution contain $\text{32 mL}$ of rubbing alcohol.

Your target solution must be $\text{5% v/v}$ rubbing alcohol, which means that every $\text{100 mL}$ of this target solution must contain $\text{5 mL}$ of rubbing alcohol.

Your first goal here will be to determine how many milliliters of rubbing alcohol must be present in this target solution.

You will have

250 color(red)(cancel(color(black)("mL solution"))) * overbrace("5 mL rubbing alc."/(100color(red)(cancel(color(black)("mL solution")))))^(color(purple)("5% v/v")) = "12.5 mL rubbing alc."

Now all you have to do is figure out what volume of the stock solution will contain this many milliliters of rubbing alcohol

12.5 color(red)(cancel(color(black)("mL rubbing alc."))) * overbrace("100 mL solution"/(32color(red)(cancel(color(black)("mL rubbing alc.")))))^(color(blue)("32% v/v")) = "39.06 mL solution"

I'll leave the answer rounded to two sig figs

"volume of stock solution needed" = color(green)(|bar(ul(color(white)(a/a)"39 mL"color(white)(a/a)|)))#