# How much pure acid must be added to 6 milliliters of a 5% acid solution to produce a 40% acid solution?

##### 1 Answer

You need to add **3.5 mL** of pure acid.

#### Explanation:

In order to solve this problem, you need to use the fact that percent concentration by volume is defined as the ratio between the volume of the solute, in your case the acid, and the volume of the solution, acid + water, multiplied by 100.

Use this equation to determine how much acid your original 6-mL sample contains

Since you're adding **pure acid** to this solution, the volume of the solute and the volume of the solution will increase by the **same amount**,

This is equivalent to

Solve this equation for

You thus need to add **3.5 mL** of *pure acid* to your original solution to get its percent concetration by volume to go from 5 to 40%.