Question

1)Suppose the reaction Ca₃(PO₄)₂ + 3H₂SO₄ → 3CaSO₄ + 2H₃PO₄ is carried out starting with 149 g of Ca₃(PO₄)₂

and 91.0 g of H₂SO₄. How much phosphoric acid will be produced?

2)For the reaction N₂(g) + 2H₂(g) → N₂H₄(l), if the percent yield for this reaction is 60.0%, what is the actual mass of hydrazine (N₂H₄) produced when 22.00 g of nitrogen reacts with 5.25 g of hydrogen?

Answer 1

Ca₃(PO₄)₂ + 3H₂SO₄ ---- > 3CaSO₄ + 2H₃PO₄

Solution: After calculation of limiting reactant we get moles of phosphoric acid

And by using molar mass we get mass in g

Calculation of moles of Ca3(PO4)2

Mol Ca(PO4)2 = Mass of Ca(PO4)2 in g / Molar mass of Ca3(PO4)2

= 149 g of Ca3(PO4)2/ 310.1767 g per mol

= 0.048

Mol H2SO4 = 91.0 g H2SO4 / 98.079 g per mol

= 0.928 mol

Limiting reactant

Mol of phosphoric acid

From moles of Ca3(PO4)2

= 0.048 mol Ca3(PO4)2 * 2 mol phosphoric acid / 1 mol Ca3(PO4)2

=0.961 mol phosphoric acid

Mol of phosphoric acid from H2SO4

= 0.928 mol H2SO4 * 2 mol phosphoric acid / 3 H2SO4

= 0.64 mol phosphoric acid

Mole of H2SO4 is limiting reactant

0.64 mol phosphoric acid

Now we multiply it by molar mass of phosphoric acid

Mass of phosphoric acid= 0.64 mol * 98 g per mol

= 6.28 g

Amount of phosphoric acid = 6.28 g

Q. 2 )

       N2(g) + 2H2(g) --- > N2H4(l)

We calculate theoretical yield

Calculation of limiting reactant :

Mol of N2 =

= 22.00 g / 28.014 g per mol

= 0.785 mol N2

Mol H2

= 5.25 g / 2.0158 g per mol

= 2.60

mol of hydrazine from mol of N2

= 0.785 mol * 1 mol hydrazine / 1mol N2

= 0.785 mol hydrazine

Mol of hydrazine from H2

= 2.60 mol H2 * 1 mol hydrazine / 2 mol H2

= 1.3 mol hydrazine

N2 is limiting reactant and mole of hydrazine produced = 0.785 mol

Mass of hydrazine = 0.785 mol * molar mass

= 0.785 mol hydrazine * 32.0456 g per mol

= 25.17 g

This is theoretical yield

Percent yield = (actual mass/ theoretical yield ) * 100

60.0 = (actual mass/ 25.17 g ) * 100

0.60 = (actual mass/ 25.17 g )

Actual mass = 15.1 g

Actual mass of hydrazine produced = 15.1 g