How can I calculate the empirical formula of an oxide?

Question

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Answer 1 · 2014-07-29T21:23:11

You calculate the molar ratios of each element in the oxide.

EXAMPLE

When a 2.50 g sample of copper is heated, it forms 3.13 g of an oxide. What is its empirical formula.

Solution

Step 1. Determine the masses

Mass of Cu = 2.50 g

Mass of O = (3.13 – 2.50) g = 0.63 g

Step 2. Determine the moles

Moles of Cu = 2.50 g Cu × #(1"mol Cu")/(63.55"g Cu")# = 0.3934 mol Cu

Moles of O = 0.63 g O × #(1"mol O")/(16.00"g O")# = 0.394 mol Cu

Step 3. Determine the Molar Ratios

#"Moles of Cu"/"Moles of O" = (0.3934"mol")/(0.394"mol") = 1/1.00 ≈ 1/1#

Step 4. Write the Empirical Formula

The empirical formula of the oxide is CuO.