Chemistry moles, molecules, ions, and molarity question

Question

A solution containing 50.8 g of sodium sulfate in a volume of 0.558 L was prepared.

1. Calculate the number of moles of sodium sulfate in this solution.
2. Calculate the number of molecules of sodium sulfate in this solution.
3. Calculate the total number of ions from the sodium sulfate in this solution.
4. What is the molarity of this solution?

Answer 1

Sodium sulfate = Na₂SO₄

molar mass = 142.0 g / mole

a) 50.8 g Na₂SO₄ x 1 mol Na₂SO₄ / 142 g = 0.358 moles Na₂SO₄

b) 0.358 moles Na₂SO₄ x 6.02x10²³ molecules / mole = 2.16x10²³ molecules of Na₂SO₄

(note: since Na₂SO₄ is a salt, we don't refer to molecules but rather formula units)

c) Na₂SO₄ ==> 2Na⁺ ions + 1 SO₄^2- ion = 3 ions from each molecule

2.16x10²³ molecules x 3 ions / molecule = 6.48x10²³ ions

d) molarity = moles Na₂SO₄ / liter = 0.358 moles / 0.558 L = 0.642 M