A 17.77 g sample of a compound contains 5.67 g of potassium, K, 5.14 g of chlorine, Cl, and oxygen, O. Calculate the empirical formula.

Question

A 17.77 g sample of a compound contains 5.67 g of potassium, K, 5.14 g of chlorine, Cl, and oxygen, O. Calculate the empirical formula.

Answer 1

Hi Nicole,

We'll need to convert the masses of each element to moles by using the molar masses on the periodic table:

However, you're not directly given the mass of O, but it's safe to assume that the remaining mass of the sample belongs to O. We'll add the masses of K and Cl and subtract that from the total mass of the sample.

Mass of O = 17.77 g - (5.67 g + 5.14 g) = 6.96 g

Now we have all 3 masses:

K = 5.67 g, Cl = 5.14 g and O = 6.96 g

Divide each by the mass on the periodic table:

K ------- 5.67/39.0983 = 0.145

Cl --------- 5.14/35.4527 = 0.145

O --------- 6.96/15.9994 = 0.435

For each element we will divide the answer by the smallest number (which is 0.145). This gives us the ratio of each atom in the formula.

For K ----- 0.145/0.145 = 1

For Cl------- 0.145/0.145 = 1

For O -------- 0.435/0.145 = 3

We will use these numbers to get the formula to get KClO₃