A sample of an oxide of arsenic is found to contain 75.74% arsenic. What is its empirical formula?

To find the empirical formula, we need to determine the ratio of arsenic to oxygen in the compound.

1. Assume that we have 100g of the compound. This means we have 75.74g of arsenic and 24.26g of oxygen (since the total must add up to 100%).

2. Next, we convert these amounts from grams to moles. The atomic mass of arsenic (As) is about 74.92 g/mol and the atomic mass of oxygen (O) is about 16.00 g/mol.

   Moles of As = 75.74g / 74.92 g/mol = 1.01 mol Moles of O = 24.26g / 16.00 g/mol = 1.52 mol

3. To find the empirical formula, we need to find the ratio of moles of As to moles of O. We do this by dividing each by the smallest number of moles calculated:

   Ratio of As = 1.01 mol / 1.01 mol = 1 Ratio of O = 1.52 mol / 1.01 mol = 1.5

4. Since we can't have half of an atom in a formula, we multiply these numbers by 2 to get whole numbers:

   Ratio of As = 1 * 2 = 2 Ratio of O = 1.5 * 2 = 3

So, the empirical formula of the oxide of arsenic is As2O3.