# If there are 100g of NaClO_2 how would you calculate the percent composition by mass of each element in NaClO_2?

Mar 1, 2016

You would calculate percent compositon by mass by first converting from grams of $N a C l {O}_{2}$ to mols of $N a C l {O}_{2}$ to find your mol to mol ratio of each element.

#### Explanation:

We are given 100g of $N a C l {O}_{2}$ and we want the mass of each individual element $\left(N a , C l , O\right)$

Step 1

Convert 100g of $N a C l {O}_{2}$ to mols
$N a$ = $22.98 g$
$C l$ = $35.45 g$
$O$ = 16.00g * 2 = $32.00 g$

$N a C l {O}_{2}$ = $\frac{90.43 g}{1 m o l}$

$100 g$ $N a C l {O}_{2}$ * $\frac{1 m o l}{90.43 g}$ = $1.11$ $m o l s$ $N a C l {O}_{2}$

Step 2

With mols of $N a C l {O}_{2}$, we can now use our mol to mol ratio and find the percent composition by mass of the three elements

$1.11$ $m o l s$ $N a C l {O}_{2}$ $\frac{1 m o l N a}{1 m o l N a C l {O}_{2}}$ * $\frac{22.98 g N a}{1 m o l N a}$ = $25.5 g$ $N a$

$1.11$ $m o l s$ $N a C l {O}_{2}$ $\frac{1 m o l C l}{1 m o l N a C l {O}_{2}}$ * $\frac{35.45 g C l}{1 m o l C l}$ = $39.3 g$ $C l$

$1.11$ $m o l s$ $N a C l {O}_{2}$ $\frac{2 m o l O}{1 m o l N a C l {O}_{2}}$ * $\frac{16.0 g O}{1 m o l O}$ = $35.5 g$ $O$

The answer comes out to 100.3g total, but this is purely from sig figs