Question

from a laboratory process designed to separate water into hydrogen and oxygen gas, a student collected 10.0 g of hydrogen and 79.4 g of oxygen. how much water was originally involved in the process?

Explanation:

Step1: Recall law of conservation of mass

In a chemical reaction, the total mass of reactants equals the total mass of products. Water is decomposed into hydrogen and oxygen here.

Step2: Calculate mass of water

The mass of water is the sum of the mass of hydrogen and oxygen produced. So, mass of water = mass of hydrogen + mass of oxygen.
Let $m_{H_2}=10.0\ g$ and $m_{O_2}=79.4\ g$. Then $m_{water}=m_{H_2}+m_{O_2}=10.0 + 79.4=89.4\ g$.

Answer:

$89.4\ g$