# Question #3e253

May 29, 2017

In 111 grams of $C a C {l}_{2}$ you have 40 grams of $C a$ due to the fact that Ca has a mass of 40 grams and Cl has a mass of 35.5 grams.
Therefore, you need to take $\frac{20 \cdot 111}{40}$ mg of $C a C {l}_{2}$ to get 20 mg/L Ca in a liter of water. It is 55.5 mg.