Question

A pharmacy wishes to mix a solution that is 5 minoxidil. She has on hand 60ml of a 4% solution and wishes to add some 7% solution to obtain the desired 5% solution. How much 7% solution should she add

Answer 1

30 ml of 7% solution should be added.

Explanation:

Given:

A solution of 5% minoxidil. On hand is 60ml of a 4% solution and wishes to add some 7% solution to obtain the desired 5% solution.

Now, to get how much 7% solution should be added.

So, we put formula to express concentration as amount of volume of solution:

c = concentration, n = substance.

`c=(n)/(v)`

Thus, the amount of substance is:

`c* v=n`

Now, in this the total amount of minoxidil is the same before and after mixing as given in question.

So, we can set the equation where V is the volume of the 7% solution:

`(60+V)5=(60* 4)+7V`

⇒
`300+5V=240+7V`

Getting the variables one side and the numbers other side we get:

⇒
`300-240=7V-5V`

⇒
`60=2V`

Dividing both sides by 2 we get:

⇒
`30=V`

Volume of the solution = 30 ml

Therefore, 30 ml of 7% solution should be added.