Determine the empirical formula of an oxide of iron which has 69.9% iron and 30.1% dioxygen by mass.

The correct option is Fe2O3.

To determine the empirical formula of the oxide of iron, we calculate the ratio of the number of moles of iron (Fe) and oxygen (O) present in the compound. Let us break down the steps below:

Step 1: Understand the given mass percentages
We are given that the compound contains:
• Iron ($\text{Fe}$) = $69.9\%$ by mass
• Dioxygen (${\text{O}}_2$, representing oxygen atoms in the compound) = $30.1\%$ by mass

If we assume we have a $100\text{g}$ sample of the iron oxide, the masses of the constituent elements will be:
• Mass of Iron ($\text{Fe}$) = $69.9\text{g}$
��� Mass of Oxygen ($\text{O}$) = $30.1\text{g}$

Step 2: Find the number of moles of each element
We use the molar masses of iron and oxygen:
• Molar mass of Iron ($\text{Fe}$) ≈ $55.85\text{g/mol}$
• Molar mass of Oxygen ($\text{O}$) ≈ $16.00\text{g/mol}$

Now, calculate the moles of each element:

$\text{Moles of Fe}=\frac{69.9\text{g}}{55.85\text{g/mol}}\approx 1.25\text{mol}$

$\text{Moles of O}=\frac{30.1\text{g}}{16.00\text{g/mol}}\approx 1.88\text{mol}$

Step 3: Determine the simplest molar ratio
Divide the number of moles of both elements by the smallest number of moles obtained (which is $1.25$):

$\text{Ratio of Fe}=\frac{1.25}{1.25}=1$

$\text{Ratio of O}=\frac{1.88}{1.25}\approx 1.5$

Step 4: Convert to the simplest whole number ratio
Since the ratio of oxygen is a decimal ($1.5$), we multiply both values by $2$ to obtain the simplest whole number ratio:
• Iron ($\text{Fe}$) = $1\times 2=2$
• Oxygen ($\text{O}$) = $1.5\times 2=3$

Therefore, the empirical formula of the oxide of iron is Fe₂O₃.