Question

A 13.00 g sample of a compound contains 4.15 g potassium (k), 3.76 g chlorine (cl), and oxygen (o). calculate the empirical formula.

Answer 1

To solve this problem, let us all convert the mass of each element into number of moles using the formula:

moles = mass / molar mass

Where,

molar mass K = 39.10 g / mol

molar mass Cl = 35.45 g / mol

molar mass O = 16 g / mol

and mass O = 13 g – 4.15 g – 3.76 g  = 5.09 g

 

moles K = 4.15 g / (39.10 g / mol) = 0.106 mol

moles Cl = 3.76 g / (35.45 g / mol) = 0.106 mol

moles O = 5.09 g / (16 g / mol) = 0.318 mol

 

The ratio becomes:

0.106 K: 0.106 Cl: 0.318 O

We divide all numbers with the smallest number, in this case 0.106. This becomes:

K: Cl: 3O

 

Therefore the empirical formula is:

$KClO_{3}$