Question

How many liters of oxygen gas at STP are needed to react completely with 8.0 of magnesium?

Answer 1

1. Write the balanced chemical equation.
2Mg + O2 → 2MgO

2. Convert grams to moles of magnesium.
\[8/24.3 = .33 mol\]
3. Use moles of magnesium to find moles of oxygen.
\[\frac{ 1 mol O2 }{ 2 mol Mg } = \frac{ x }{ .33 mol Mg}\]
\[x = \frac{ .33 }{ 2 } = .166 mol O2\]
5. One mole of an ideal gas will occupy a volume of 22.4 liters at STP. If you know one mole of O2 takes up 22.4 liters, you can find how much 4 moles will take up.
\[\frac{ 1 mol }{ 22.4 L } = \frac{ .166 mol }{ x }\]
6. Solve for x (liters)
\[x = (.166)(22.4 L) = 3.7 L\]

Answer: 3.7 liters O2