Question

20.4 g of carbon reacts with 54.4 g of oxygen. What is the empirical formula for this compound?

Answer 1

Atomic mass of carbon (C) is 12.0, i.e. 1 mole carbon is 12.00 g. Therefore, 20.4 g of carbon = 1.7 moles

Atomic mass of oxygen (O) is 16.0, i.e.

1 mole oxygen is 16.0 g. Therefore, 54.4 g of oxygen = 3.4 moles

Therefore, the compound contains 1.7 moles of C and 3.4 moles of O.

The molecular formula is C_1.7O_3.4 i.e. CO₂ (remember that during writing chemical formula, less electronegative elements will be kept at left side. Here C is less electronegative element than O. So the formula is written as CO₂ but not O₂C)