Understanding the Concepts

* Law of Conservation of Mass: In a chemical reaction, the total mass of the reactants (starting materials) must equal the total mass of the products (substances formed).

* Electrolysis of Water: The process of separating water into hydrogen and oxygen gas is called electrolysis.

Solving the Problem

1. Identify the reactants and products:

* Reactant: Water (H₂O)

* Products: Hydrogen gas (H₂) and Oxygen gas (O₂)

2. Apply the Law of Conservation of Mass:

* The mass of the water (reactant) must equal the combined mass of the hydrogen and oxygen (products).

3. Set up the equation:

* Mass of water = Mass of hydrogen + Mass of oxygen

* 178.8 grams = Mass of hydrogen + 20.0 grams

4. Solve for the mass of hydrogen:

* Mass of hydrogen = 178.8 grams - 20.0 grams = 158.8 grams

Answer: The mass of hydrogen gas produced is 158.8 grams.