# How many liters each of 15% acid and 33% acid should be mixed to get 120 L of 21% acid?

Jul 24, 2018

The volume of 15% is $= 80 L$ and the volume of 33% is $= 40 L$

#### Explanation:

Perform a material balance

The total volume is $= 120 L$

Let the volume of 15% acid be $= v L$

Then,

The volume of 33% acid is $= \left(120 - v\right) L$

The final percentage is =21% acid

Therefore,

$v \cdot \frac{15}{100} + \left(120 - v\right) \cdot \frac{33}{100} = 120 \cdot \frac{21}{100}$

$15 v + 120 \cdot 33 - 33 v = 120 \cdot 21$

$18 v = 120 \left(33 - 21\right) = 1440$

$v = \frac{1440}{18} = 80 L$