Question

A pharmacist wishes to mix a solution that is 4% Minoxidil. She has on hand 60 ml of a 3% solution and wishes to add some 6% solution to obtain the desired 4% solution. How much 6% solution should she add?

Answer 1

She should add 30ml.

Explanation:

We can express concentration as amount of solute/volume of solution or:

`c=n/v`

So the amount of substance `n` is given by:

`n=cxxv`

In this problem the total amount of `"Minoxidil"^("tm")` is the same before and after mixing, so we can set up this equation where `V` is the volume of the 6% solution:

`(60+V)4=(60xx3)+6V`

`:.240+4V=180+6V`

`:.6V-4V=240-180`

`:.2V=60`

`V=60/2=30"ml"`