Question

Through 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.) Report your answer to the nearest tenth

Answer 1

126.0g of water were initially present

Step-by-step explanation:

The electrolysis of water occurs as follows:

2H₂O(l) ⇄ 2H₂(g) + O₂(g)

Where 2 moles of water produce 2 moles of hydrogen and 1 mole of oxygen.

To find the mass of water we need to determine moles of oxygen and hydrogen, thus:

Moles Hydrogen:

14.0g H₂ ₓ (1mol / 2g H₂) = 7 moles H₂

Moles Oxygen:

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

Based on the chemical equation, the moles of water initially present were 7 moles (That produce 7 moles H₂ and 3.5 moles O₂). The mass of 7 moles of H₂O is:

7 moles H₂O * (18g / mol) =

126.0g of water were initially present