How many moles are in 15.5 g SiO_2?

Feb 20, 2016

About a 1/4 of a mole.

Explanation:

Silicon dioxide has a molar mass of $60.08$ $g$ $m o {l}^{-} 1$. What does this mean? It means that Avogadro's number of $S i {O}_{2}$ units has a mass of $60.08$ $g$.

So to find the molar quantity of silicon dioxide, all I have to do is divide the mass by the molar mass:

$\text{Moles of silicon dioxide " = "Mass"/"Molar Mass}$

$=$ $\frac{15.5 \cdot \cancel{g}}{60.08 \cdot \cancel{g} \cdot m o {l}^{-} 1}$ $=$ ?? $m o l$

By doing the equation with units included it helps to prevent me from making mistakes. Should I divide or should I multiply? The fact that the calculation gave me an answer in moles persuades me that I did the right thing. It's all too easy to make a mistake.

What is silicon dioxide? How do you calculate its molar mass?