Question

A 4.08 g sample of a compound of nitrogen and oxygen contains 3.02 g of oxygen. What is the empirical formula?

Answer 1

The empirical formula is `"N"_4"O"`.

Explanation:

An empirical formula is the lowest whole number ratio of elements in a compound. Each ratio will be the subscript of each element.

Determine the mass of each element in grams.

`"N":` `"4.08 g"-"3.02g"="1.06 g"`

`"O":` `"3.02 g"` (given)

Determine moles of each element by dividing the mass of each element by its molar mass (atomic weight on the periodic table in g/mol.

`"N":` `"1.06 g N"/"14.007 g/mol"="0.0756764 mol N"`

`"O":` `"3.02 g O"/"15.999 g/mol"="0.188761 mol O"`

Determine mole ratios by dividing the moles of each element by the least number of moles.

`"N":` `"0.0756764 mol"/"0.188761 mol"="4.01"~~4`

`"O":` `"0.188761 mol"/"0.188761"=1.00=1`

The empirical formula is `"N"_4"O"`.

The compound with this formula is called nitrosylazide with the following structure.

For more examples of this type of empirical formula problem, check out the following website: http://www.chemteam.info/Mole/Emp-formula-given-mass-data.html

For examples of determining an empirical formula from percent composition, check out this website: https://www.chem.tamu.edu/class/majors/tutorialnotefiles/empirical.htm