Question #a4ff2

1 Answer
Apr 5, 2016

Answer:

#"39 mL"#

Explanation:

Your stock solution is #"32% v/v"# isopropyl alcohol, which is commonly called rubbing alcohol, which means that every #"100 mL"# of this stock solution contain #"32 mL"# of rubbing alcohol.

Your target solution must be #"5% v/v"# rubbing alcohol, which means that every #"100 mL"# of this target solution must contain #"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)|)))#