# A certain ionic compound is found to contain .012 mol of sodium, .012 mol of sulfur, and .018 mol of oxygen. What is its empirical formula?

##### 1 Answer

#### Explanation:

A compound's **empirical formula** tells you what the **smallest whole number ratio** between the elements that make up that compound is.

In your case, you know that this ionic compound contains

#0.012# moles of sodium#0.012# moles of sulfur#0.018# moles of oxygen

To get the mole ratio that exists between these elements in the compound, divide these numbers by the *smallest one*

#"For Na: " (0.012color(red)(cancel(color(black)("moles"))))/(0.012color(red)(cancel(color(black)("moles")))) = 1#

#"For S: " (0.012color(red)(cancel(color(black)("moles"))))/(0.012color(red)(cancel(color(black)("moles")))) = 1#

#"For O: " (0.018color(red)(cancel(color(black)("moles"))))/(0.012color(red)(cancel(color(black)("moles")))) = 1.5#

Now, since you can't have *fractional numbers* as mole ratios, you will need to find the *smallest whole number ratio* that satisfies the condition

Notice that if you multiply all the numbers by

#("Na"_1"S"_1"O"_1.5)_2 implies "Na"_2"S"_2"O"_3#

For *ionic compounds*, the empirical formula is always the same as the chemical formula, which is why you cn say that your unknown compound is actually *sodium thiosulfate*,