A compound contains 38.7% K, 13.9% N, and 47.4% O by mass. What is the empirical formula of the compound? A) KNO₂ B) K₄NO₅ C) KNO₃ D) K₂NO₃ E) K₂N₂O₃

Question

Quizplus · Accepted Answer

To determine the empirical formula, we need to find the smallest whole number ratio of atoms in the compound. 
Assume that we have a 100g sample, this means we have 38.7g K, 13.9g N, and 47.4g O. 
Next, we need to convert these masses to moles by dividing by their respective molar masses: 
38.7g K / 39.10 g/mol = 0.989 moles K 
13.9g N / 14.01 g/mol = 0.992 moles N 
47.4g O / 15.99 g/mol = 2.963 moles O

The next step is to divide each of the mole values by the smallest mole value to get the mole ratio: 
0.989 mol K / 0.989 mol = 1.00 (or 1) 
0.992 mol N / 0.989 mol = 1.01 (or ~1) 
2.963 mol O / 0.989 mol = 3.00 (or 3)

Therefore, the empirical formula is KNO3, with a 1:1:3 ratio of K, N, and O atoms. 
The correct answer choice is C.

A Compound Contains 38