# Calculate the empirical formula for the compound found to contain 2.82g/Na, 4.35g/Cl and 7.83g/O. My biggest question is, when you get to the step where you divide all three subscripts, by the smallest number, how do I get rid of the decimal?

##### 1 Answer

You round to the nearest integer.

#### Explanation:

You know that your compound contains **2.82 g** of sodium, **4.35 g** of chlorine, and **7.83 g** of oxygen.

What you do next is use each element's molar mass to try and find how many *moles of each* you get in that sample of the compound.

In this case, you have

#"For Na: " (2.82color(red)(cancel(color(black)("g"))))/(23.0color(red)(cancel(color(black)("g")))/"mol") = "0.1226 moles Na"#

#"For Cl: "(4.35color(red)(cancel(color(black)("g"))))/(35.45color(red)(cancel(color(black)("g")))/"mol") = "0.1227 moles Cl"#

#"For O: "(7.83color(red)(cancel(color(black)("g"))))/(16.0color(red)(cancel(color(black)("g")))/"mol") = "0.4894 moles O"#

Now, the reason you divide these numbers by the *smallest* one is so that you ahve an idea of the **mole ratios** that exist between the elements that make up the compound.

In this case, you have

#"For Na: " (0.1226color(red)(cancel(color(black)("moles"))))/(0.1226color(red)(cancel(color(black)("moles")))) = 1#

#"For Cl: " (0.1227color(red)(cancel(color(black)("moles"))))/(0.1226color(red)(cancel(color(black)("moles")))) =1.001#

#"For O: " (0.4894color(red)(cancel(color(black)("moles"))))/(0.1226color(red)(cancel(color(black)("moles")))) = 3.992#

So, what do you do with the numbers that hav a decimal? You *round them to the nearest integer*.

For

#"For Cl: " 1.001 ~~ 1#

For

#"For O: " 3.992 ~~ 4#

This means that the *empirical formula*, which tells you what the **smallest integer ratio of atoms** you get in a compound, will be

#"Na"_1"Cl"_1"O"_4 " "# , or#" " "NaClO"""_4#