Question

measurements show that unknown compound x has the following composition:

element | mass %
chromium | 68.5%
oxygen | 31.6%

write the empirical chemical formula of x.

Explanation:

Step1: Assume 100g of compound X

So, mass of Cr = 68.5g, mass of O = 31.6g.

Step2: Calculate moles of Cr

Molar mass of Cr = 52 g/mol. Moles of Cr = $\frac{68.5}{52} \approx 1.317$ mol.

Step3: Calculate moles of O

Molar mass of O = 16 g/mol. Moles of O = $\frac{31.6}{16} \approx 1.975$ mol.

Step4: Find mole ratio

Divide moles by the smallest (1.317):
Cr: $\frac{1.317}{1.317} = 1$
O: $\frac{1.975}{1.317} \approx 1.5$
Multiply by 2 to get whole numbers: Cr = 2, O = 3.

Answer:

$\text{Cr}_2\text{O}_3$