Composition of aluminum in aluminum oxide

1. A 3.53-gsample of aluminum completely reacts with oxygen to form 6.67gof aluminum oxide. Use this data to calculate the mass percent composition of aluminum in aluminum oxide.

2. A 1.912-g sample of calcium chloride is decomposed into its constituent elements and found to contain 0.690 gCa and 1.222 gCl.

Calculate the mass percent composition of Ca and Cl in calcium chloride.

Enter your answers numerically separated by a comma.

3. A 1.45-g sample of phosphorus burns in air and forms 2.57 g of a phosphorus oxide.

Calculate the empirical formula of the oxide.

Express your answer as a chemical formula.

4. Copper (II) fluoride contains 37.42 % F by mass.

Use this percentage to calculate the mass of fluorine in grams contained in 34.5 g of copper (II) fluoride.