Question

measurements show that unknown compound x has the following composition: element mass % calcium 38.7% phosphorus 19.9% oxygen 41.2% write the empirical chemical formula of x.

Explanation:

Step1: Assume 100g of compound

We assume 100g of compound X, so mass of Ca = 38.7g, P = 19.9g, O = 41.2g.

Step2: Calculate moles of each element

Molar - mass of Ca = 40.08g/mol, moles of Ca $n_{Ca}=\frac{38.7g}{40.08g/mol}\approx0.966mol$. Molar - mass of P = 30.97g/mol, moles of P $n_{P}=\frac{19.9g}{30.97g/mol}\approx0.642mol$. Molar - mass of O = 16.00g/mol, moles of O $n_{O}=\frac{41.2g}{16.00g/mol}=2.575mol$.

Step3: Find mole - ratio

Divide each mole value by the smallest mole value (0.642mol). For Ca: $\frac{0.966mol}{0.642mol}\approx1.5$. For P: $\frac{0.642mol}{0.642mol}=1$. For O: $\frac{2.575mol}{0.642mol}\approx4$. Multiply all by 2 to get whole - numbers. So, the ratio of Ca : P : O is 3 : 2 : 8.

Answer:

$Ca_3P_2O_8$