Question

Nts) How many moles of oxygen gas are needed to react completely with 23.6 mL Mg, which has a density of 1.74 g/mL? unbalanced equation: Mg + O2 “yields”/ MgO

0.845 mol O2
1.12 mol O2
3.38 mol O2
20.5 mol O2

Answer 1

Answer is: 0.845 moles of oxygen gas are needed.

Balanced chemical reaction: 2Mg + O₂ → 2MgO.
V(Mg) = 23.6 mL.
d(Mg) = 1.74 g/mL.
m(Mg) = V(Mg) · d(Mg).
m(Mg) = 23.6 mL · 1.74 g/mL.
m(Mg) = 41.064 g; mass of magnesium.
n(Mg) = m(Mg) ÷ M(Mg).
n(Mg) = 41.064 g ÷ 24.3 g/mol.
n(Mg) = 1.69 mol.
From chemical reaction: n(Mg) : n(O₂) = 2 : 1.
n(O₂) = n(Mg) ÷ 2.
n(O₂) = 1.69 mol ÷ 2.
n(O₂) = 0.845 mol.