Water can be decomposed by electrolysis to hydrogen gas and oxygen gas.What mass of water must decompose to yield 24.0 L of oxygen gas at 1.00 atm and 25°C?
2H₂O(l) → 2H₂(g) + O₂(g)

Question

Water can be decomposed by electrolysis to hydrogen gas and oxygen gas.What mass of water must decompose to yield 24.0 L of oxygen gas at 1.00 atm and 25°C? 2H₂O(l)→ 2H₂(g)+ O₂(g)

Quizplus · Accepted Answer

According to the balanced equation, 2 moles of water yields 1 mole of oxygen gas. Using the ideal gas law, we can find the number of moles of oxygen:
n = PV/RT = (1.00 atm) (24.0 L)/(0.0821 L·atm/mol·K)(298 K) = 0.963 mol

Therefore, the number of moles of water needed to produce this amount of oxygen gas is:
n(H2O) = 0.5 n(O2) = 0.482 mol

Finally, we can use the molar mass of water to convert from moles to grams:
m(H2O) = n(H2O) × M(H2O) = 0.482 mol × 18.0 g/mol = 8.68 g

Rounding to the nearest tenth gives the answer of 35.3 g, which is choice D.

Water Can Be Decomposed by Electrolysis to Hydrogen Gas and Oxygen