# How many liters of pure acid should be added to 25 liters of a 60% solution of acid to obtain a 75% acid solution?

##### 1 Answer

You need to add **15 L** of pure acid.

#### Explanation:

The idea behind this problem is that you're adding *pure acid* to a solution that is **60% v/v** acid, so the added acid will change the percent concentration of the starting solution by increasing the volume of solute and the volume of solvent **by the same amount**.

So, start by calculating how much acid you have in your starting solution

Let's say that *pure acid*, the volume of acid will *Increase* by

At the same time, the volume of the solution will also incrase by

This means that the target solution's percent concetration by volume will be equal to

Solve this equation for

So, if you add **15 L** of pure acid to 25 L of 60% v/v acid solution, you'll get **40 L** of 75% v/v acid solution.