Question

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

Answer 1

You would calculate percent compositon by mass by first converting from grams of `NaClO_2` to mols of `NaClO_2` to find your mol to mol ratio of each element.

Explanation:

We are given 100g of `NaClO_2` and we want the mass of each individual element `(Na, Cl, O)`

Step 1

Convert 100g of `NaClO_2` to mols
`Na` = `22.98g`
`Cl` = `35.45g`
`O` = 16.00g * 2 = `32.00g`

`NaClO_2` = `(90.43g)/(1mol)`

`100g` `NaClO_2` * `(1mol)/(90.43g)` = `1.11` `mols` `NaClO_2`

Step 2

With mols of `NaClO_2`, we can now use our mol to mol ratio and find the percent composition by mass of the three elements

`1.11` `mols` `NaClO_2` `(1mol Na)/(1mol NaClO_2)` * `(22.98g Na)/(1mol Na)` = `25.5g` `Na`

`1.11` `mols` `NaClO_2` `(1mol Cl)/(1mol NaClO_2)` * `(35.45g Cl)/(1mol Cl)` = `39.3g` `Cl`

`1.11` `mols` `NaClO_2` `(2mol O)/(1mol NaClO_2)` * `(16.0g O)/(1mol O)` = `35.5g` `O`

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