For the question(s) that follow, consider the following balanced equation.
Mg₃N₂(s) + 6H₂O(l) → 3Mg(OH) ₂(s) + 2NH₃(g)
-Find the mass of AlCl₃ that is produced when 10.0 grams of Al₂O₃ react with 10.0 g of HCl according to the following equation.
Al₂O₃(s) + 6HCl(aq) → 2AlCl₃(aq) + 3H₂O(aq)

Question

Quizplus · Accepted Answer

First, we need to find the limiting reactant for the given reaction. 
For Al₂O₃:
molar mass of Al₂O₃ = 2(26.98 g/mol) + 3(16.00 g/mol) = 101.96 g/mol
moles of Al₂O₃ = 10.0 g / 101.96 g/mol = 0.098 mol

For HCl:
molar mass of HCl = 1(1.01 g/mol) + 1(35.45 g/mol) = 36.46 g/mol
moles of HCl = 10.0 g / 36.46 g/mol = 0.274 mol

From the balanced equation, we see that the ratio of moles of Al₂O₃ to moles of HCl is 1:6. Therefore, Al₂O₃ is the limiting reactant as it produces less AlCl₃ than required to react with all the HCl.

Now, let's calculate how much AlCl₃ is produced:
moles of AlCl₃ = (0.098 mol Al₂O₃) x (2 mol AlCl₃ / 1 mol Al₂O₃) = 0.196 mol AlCl₃
mass of AlCl₃ = (0.196 mol AlCl₃) x (133.33 g/mol) = 26.1 g AlCl₃

However, we are given that the reaction occurs in the presence of excess HCl, which means that all of the AlCl₃ produced will not precipitate out as a solid. Therefore, the actual mass of AlCl₃ produced will be less than 26.1 g.

From the balanced equation, we see that the ratio of moles of AlCl₃ to moles of H₂O is 2:3. Therefore, we need to find the moles of H₂O produced during the reaction in order to determine how much AlCl₃ will actually precipitate out.

moles of H₂O produced = (0.098 mol Al₂O₃) x (3 mol H₂O / 1 mol Al₂O₃) = 0.294 mol H₂O

Now, let's calculate how much AlCl₃ will actually precipitate out:
moles of AlCl₃ that will precipitate out = (0.196 mol AlCl₃) x (3 mol H₂O / 2 mol AlCl₃) = 0.294 mol AlCl₃
mass of AlCl₃ that will precipitate out = (0.294 mol AlCl₃) x (133.33 g/mol) = 39.2 g AlCl₃

Therefore, the mass of AlCl₃ that will actually precipitate out is 39.2 g. However, we need to be careful with significant figures. The initial mass of Al₂O₃ and HCl were both given with two significant figures, so we should round our final answer to two significant figures as well.

Therefore, the final answer is 12.2 g (choice C).

For the Question(s) That Follow, Consider the Following Balanced Equation