Kavita.docx

1. A 10.000 g sample of an oxide of copper was found to contain 8.882 g of copper. Determine the empirical formula of the copper oxide. Ans:

2. 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. Ans:

3. 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.

4. 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. Ans:

5. 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.

6. 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. 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. Ans:

7. Deduce the total number of atoms and molecules in: (a) one molecule of methane. (b) one mole of methane. (c) 1.605 g of methane. Ans:

8. What is the mass of: (a) One mole of sodium chloride, NaCl? (b) 2.00 x 10-2 mol of glucose, C6H12O6? (c) 3.62 mol of magnesium oxide, MgO? Ans:

9. What is the mass of: (a) 6.02 x 1023 atoms of sulfur, S? (b) 3.01 x 1022 iron(II) ions, Fe2+? (c) 1.204 x 1024 molecules of water, H2O? Ans:

10. What amount (in mol) is present in: (a) 100 g of calcium carbonate, CaCO3? (b) 132 g of carbon dioxide, CO2? (c) 2.497 g of copper(II) sulfate pentahydrate, CuSO4.5H2O? Ans:

11. How many atoms are present in: (a) 6.41 g of sulfur dioxide, SO2? (b) 262.6 g of xenon, Xe? (c) 3.603 g of aspirin, C9H8O4? Ans:

12.Deduce the number of nitrogen atoms in: (a) 5.00 x 10-3 mol of ammonia, NH3. (b) 14.01 g of nitrogen gas, N2. (c) 4.601 g of nitrogen dioxide, NO2. Ans: