hrough the complete electrolysis of a sample of pure water, a student collects 14.0 grams of hydrogen gas and 112.0 grams of oxygen gas. What mass of water (in grams), if it reacted completely, was initially present? (The electrolysis of water is the use of an electric current to decompose it into its component elements.)

126g of H₂O

Explanation:

Electrolysis of water is:

2H₂O(l) → 2H₂(g) + O₂(g).

To know mass of water that reacted, we need to find moles of hydrogen and oxygen and, by using electrolysis chemical equation, we can determine moles of water and its mass, thus:

Moles hydrogen (Molar mass: 2.01g/mol):

14.0g H₂ * (1mol / 2.01g) = 6.97 moles hydrogen

Moles Oxygen (Molar mass: 32g/mol):

112.0g O₂ * (1 mol / 32g) = 3.5 moles oxygen

As 2 moles of hydrogen and 1 mole of oxygen are produced from 2 moles of water, and 7 moles of hydrogen and 3.5 moles of oxygen were collected, moles of water that reacted were 7 moles H₂O.

As molar mass of water is 18g/mol, mass of 7 moles of H₂O is:

7 mol H₂O * (18g / mol) =