Chemistry 120 Lab Question

Question

1. upon heating a 4.250 gram sample of Na2SO4 x nH2O sample loses 2.388 grams upon heating. What is n for this hydrate?

Answer 1

mass of H₂O = 2.388 g

moles H₂O = 2.388 g H₂O x 1 mol H₂O / 18 g = 0.1327 moles H₂O

mass of Na₂SO₄ = 4.250 g - 2.388 g = 1.862 g Na₂SO₄ anhydrous

moles Na₂SO₄ = 1.862 g Na₂SO₄ x 1 mol Na₂SO₄ / 142.0 g = 0.01311 moles Na₂SO₄

If we divide moles H₂O and moles Na₂SO₄ by 0.01311 to get whole numbers, we end up with

moles Na₂SO₄ = 0.01311 / 0.01311 = 1 mol Na₂SO₄

moles H₂O = 0.1327 / 0.01311 = 10 which means n = 10

The formula of the hydrate would be Na₂SO₄ • 10H₂O