Empirical & molecular formula questions

Assignment: Questions on Empirical & molecular formula

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10.000 g of a sample of an oxide of copper was found to contain 8.882 g of copper.
Determine the empirical formula of the copper oxide.

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A salt was found to contain 11.33 % carbon, 43.38 % sodium and 45.29 % oxygen by mass.
Determine the empirical formula of the salt.

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A hydrocarbon contains 92.24 % carbon by mass and has a molar mass of 78.12 g mol−1.
Determine the empirical formula and molecular formula of the hydrocarbon.

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Aspirin contains 60.00 % carbon, 4.48 % hydrogen and 35.52 % oxygen. It has a molar mass of 180.17 g mol−1.
Determine the empirical and molecular formula of aspirin.

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An organic compound has a molar mass less than 100 g mol−1. The percentage composition by mass of this compound is: 71.38 % carbon, 9.60 % hydrogen with the remainder being oxygen.
Determine the empirical and molecular formula of this compound.

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A piece of magnesium with a mass of 5.867 g was heated in a crucible which was open to the air. After the magnesium had combusted and allowed to cool down the product was found to have a mass of 8.956 g.

i. Determine the empirical formula of the magnesium oxide formed.

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ii. The actual empirical formula of magnesium oxide is MgO.
Suggest three possible reasons why the value obtained in the experiment described above did not produce the correct formula.

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