Question

A sample of a compound contains 7.89 g potassium, 2.42 g carbon, and 9.69 g oxygen. What is the empirical and molecular formulas of this compound, which has a molar mass of 198.22 g/mol?

Answer 1

The empirical formula is `KCO_3`. The molecular formula is `K_2C_2O_6`

Explanation:

Let the molecular formula be `K_mC_nO_p`

The weight of the sample is

`m=7.89+2.42+9.69=20g`

The number of moles of each element is

Potassium `=7.89/39.1=0.2`

Carbon `=2.42/12=0.2`

Oxygen `=9.69/16=0.6`

Divide by `0.2`

Potassium `=0.2/0.2=1`

Carbon `=0.2/0.2=1`

Oxygen `=0.6/0.2=3`

Therefore,

The empirial formula is `KCO_3`

Since the molar mass is `=198.22`

and

`M_K+M_C+M_O=39+12+3*16=99`

The molecular formula is `K_2C_2O_6`

And the name of this compound is probably

Potassium peroxydicarbonate