AP Chemistry - Avogadro's Number and Moles Exercise Sheet 1. What are the units of molar mass? 2. The mass of 2.5 X 104 grapes is 50 kilograms, and that of an equal number of oranges is 1.2 X 103 kg.  What is the mass ratio of a single single grape to a single orange? 3. A mole of carbon atoms has a mass of 12 grams, and a mole of magnesium atoms, 24 grams. What is the mass ratio of a single carbon atom to a single magnesium atom? 4. Aluminum and oxygen combine in a mass ratio of 9.00 to 8.00.  If a flashbulb contains 5.4 X 10-3 grams of aluminum, what mass of oxygen must be present for complete combustion of the aluminum? 5. If there are 'x' atoms in 5 grams of carbon, how many atoms are there in 5 grams of silicon? 6. If 10 grams of iron contain 'y' atoms, how many grams of aluminum will contain 'y' atoms. 7. If  8 grams of oxygen contain 3.01 X 1023 atoms, calculate the number of atoms present in 2 grams of oxygen. 8. Using Avogadro's number, calculate the number of atoms in 0.005 kilograms of carbon.