Question 1:

When 0.2250 g of magnesium is heated with 0.5331 g of nitrogen in a closed container, the magnesium is completely 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.

1) Reaction: 3Mg + N₂ → Mg₃N₂.

m (Mg) = 0,225 g

n (Mg) = 0,225 g : 24,3 g/mol = 0,009 mol.

n (Mg) : n (N₂) = 3 : 1

n₁ (N₂) = 0,003 mol.

n₂ (N₂) = 0,5331 : 28 = 0,019 mol.

n₃ (N₂) = 0,019 mol - 0,003 mol = 0,016, m (N₂) = 0,016mol·28g/mol=0,4467g.

or simpler: m (N₂) = 0,225 g + 0,5331 - 0,3114 g = 0,4467 g.

2) Answer is: 6 of fluorine atoms are combined with one uranium atom.

m (U) = 209 g.

m (F) = 100 g.

n (U) = m (U) : M (U)

n (U) = 209 g : 238 g/mol.

n (U) = 0,878 mol.

n (F) = m (F) : M (F)

n (F) = 5,263 mol

n (U) : n (F) = 0,878 mol : 5,263 mol / : 0,878.

n (U) : n (F) = 1 : 6.

n - amount of substance