# Solid bismuth oxide can react with carbon to form bismuth metal and carbon monoxide. How many grams of bismuth oxide reacted if 60.7 grams of bismuth is formed?

The answer is $67.6$ $g$.
$B {i}_{2} {O}_{3 \left(s\right)} + 3 {C}_{\left(s\right)} \to 2 B {i}_{\left(s\right)} + 3 C {O}_{\left(g\right)}$
We know the molar masses of $B i$ ($209 \frac{g}{m o l}$) and $B {i}_{2} {O}_{3}$ ($466 \frac{g}{m o l}$), and the mole-to-mole ratio between $B i$ and $B {i}_{2} {O}_{3}$, so we could say that
$60.7 g B i \cdot \frac{1 m o l e B i}{209 g} \cdot \frac{1 m o l e B {i}_{2} {O}_{3}}{2 m o l e s B i} \cdot \frac{466 g}{1 m o l e B {i}_{2} {O}_{3}} = 67.6 g B {i}_{2} {O}_{3}$