AP Chem Titrations

Question

Limestone can be considered to essentially be calcium carbonate. Acid rain, for the purposes of the question, will be considered sulfuric acid. When limestone buildings are eroded by acid rain the unbalanced reaction can be summarized as:

___CaCo3 (s) + ___H2SO4 (aq) + ___CO2 (g) + ___ H2O (l)

a. This reaction can be replicated by performing a titration. If 7.21 grams of calcium carbonate is added to 1.20 L of 0.211 M sulfuric acid, how many moles of acid will remain after the reaction?

b. What volume of 0.400 M potassium hydroxide must be added to neutralize the excess acid?

___KOH (aq) + ___H2SO4 (aq) ---> ___K2SO4 (aq) + H2O (l)

Answer 1

CaCO₃ (s) + H₂SO₄ (aq) ==> CaSO₄ + CO₂ (g) + H₂O (l) ... balanced equation

7.21 g.......1.2L x 0.211M

mols CaCO₃ = 7.21 g CaCO₃ x 1 mol / 100 g = 0.0721 mols

mols H₂SO₄ = 1.2 L x 0.211 mol/L = 0.2532 mols

Limiting reactant = CaCO₃

mols H₂SO₄ ued = 0.0721 mols CaCO₃ x 1 mol H₂SO₄ / mol CaCO₃ = 0.0721 mols H₂SO₄ used

mols H₂SO₄ left over = 0.2532 mols - 0.0721 mol = 0.2261 mols H₂SO₄ left over

2KOH + H₂SO₄ ==> K₂SO₄ + 2H₂O ... balanced equation

0.2261 mols H₂SO₄ x 2 mol KOH / mol H₂SO₄ = 0.4522 mols KOH needed

0.4522 mols KOH x 1 L / 0.400 mols = 1.13 L KOH needed