# A recipe for chili calls for 3 g of sodium chloride. How many formula units of NaCl is that?

Feb 29, 2016

$3$ $g$ is $0.075$ $m o l$ of $N a C l$. Multiply this by Avogadro's number to find that this amount of salt contains $4.5 \times {10}^{22}$ formula units of $N a C l$.

#### Explanation:

First find the number of moles.

The molar mass is $23 + 17 = 40$ $g m o {l}^{-} 1$, so $n = \frac{m}{M} = \frac{3}{40} = 0.075$ $m o l$.

Now one mole of any substance contains Avogadro's number, $6.02 \times {10}^{23}$ units of that substance: in this case formula units (one $N a$ and one $C l$) of $N a C l$.

That means the $3$ $g$ of salt (and therefore the chili) will contain $4.5 \times {10}^{22}$ formula units of $N a C l$.