Question

determine the % composition of iron in iron(iii) carbonate. ~report 2 significant digits and the % sign ~

Explanation:

Step1: Find formula of iron(III) carbonate

Iron(III) carbonate has the formula $\text{Fe}_2(\text{CO}_3)_3$

Step2: Calculate molar mass of compound

First, get atomic masses: $\text{Fe}=55.85\ \text{g/mol}$, $\text{C}=12.01\ \text{g/mol}$, $\text{O}=16.00\ \text{g/mol}$
Molar mass = $2\times55.85 + 3\times(12.01 + 3\times16.00)$
$= 111.7 + 3\times(12.01 + 48.00)$
$= 111.7 + 3\times60.01$
$= 111.7 + 180.03 = 291.73\ \text{g/mol}$

Step3: Calculate total mass of Fe in compound

Total Fe mass = $2\times55.85 = 111.7\ \text{g/mol}$

Step4: Compute mass percent of Fe

Mass % = $\frac{\text{Total mass of Fe}}{\text{Molar mass of compound}} \times 100\%$
$= \frac{111.7}{291.73} \times 100\% \approx 38.29\%$

Step5: Round to 2 significant digits

Round $38.29\%$ to 2 sig figs: $38\%$

Answer:

38%