Ex 4: A compound is found to be 42.1 % sodium, 18.9 %phosphorous, and the rest oxygen. What is the empirical formula

To find the empirical formula, follow these steps:

1. Assume you have 100g of the compound. This means you have 42.1g of sodium, 18.9g of phosphorous, and the rest (100g - 42.1g - 18.9g = 39g) is oxygen.

2. Convert the mass of each element to moles. The atomic mass of sodium is approximately 23g/mol, phosphorous is approximately 31g/mol, and oxygen is approximately 16g/mol.

   So, you have:

   • Sodium: 42.1g / 23g/mol = 1.83 mol
   • Phosphorous: 18.9g / 31g/mol = 0.61 mol
   • Oxygen: 39g / 16g/mol = 2.44 mol

3. Divide each mole quantity by the smallest number of moles calculated (which is for phosphorous, 0.61 mol) to get the ratio of atoms:

   • Sodium: 1.83 mol / 0.61 mol = 3
   • Phosphorous: 0.61 mol / 0.61 mol = 1
   • Oxygen: 2.44 mol / 0.61 mol = 4

So, the empirical formula of the compound is Na3P1O4, or simply Na3PO4.