Question 1:

When 0.2250 g of magnesium is heated with 0.5331 g of nitrogen in a closed container, the magnesium iscompletely converted to 0.3114 g of magnesium nitride. What mass of unreacted nitrogen must remain?

 Question 2:

A compound of uranium and fluorine is used to generate uranium for nuclear power plants. The gas can be decomposed to yield 2.09 parts by mass of uranium for every 1 part by mass of fluorine. If the relative mass of a uranium atom is 238 and the relative mass of a fluorine atom is 19,  calculate the number of fluorine atoms that are combined with one uranium atom.