The empirical formula of the oxide is Co₂O₃.
<em>Step 1</em>. Calculate the <em>mass of oxygen</em>
Your reaction is
Cobalt + oxygen ⟶ cobalt oxide
29.05 g + x g ⟶ 40.88 g
According to the <em>Law of Conservation of Mass</em>, the total mass of the reactants must equal the total mass of the products. Thus,
29.05 g + <em>x</em> g ⟶ 40.88 g
<em>x</em> = 40.88 – 29.05 = 11.83
<em>Step 2</em>. Calculate the <em>moles of each element</em>
The empirical formula is the simplest whole-number ratio of atoms in a compound.
The ratio of atoms is the same as the ratio of moles.
So, our job is to calculate the molar ratio of Co to O.
<em>Moles of Co</em> = 29.05 g Co × (1 mol Co /(58.93 g Co) = 0.492 96 mol Co
<em>Moles of </em>O = 11.83 g O × (1 mol O/16.00 g O) = 0.739 38 mol O
<em>Step 3</em>. Calculate the <em>molar ratio</em> of the elements
Divide each number by the smaller number of moles
Co:O = 0.429 26:0.739 38 = 1:1.4999
<em>Step 4</em>. Multiply each number by a factor that makes the <em>ratio close to whole numbers
</em>
Multiply by 2. Then
Co:O = 2:2.998 ≈ 2:3
<em>Step 5</em>: Write the <em>empirical formula</em>
EF = Co₂O₃
