Question

How many grams of Na₂SO₄ (MW 142 g/mol) are required to make 1.2 liters of 0.5 N solution?

Answer 1

To make a 1.2 L 0.5 N solution of Na₂SO₄, you need 42.6 grams of Na₂SO₄. The calculation involves converting normality to molarity, then calculating the number of moles needed, and finally finding the mass based on the molar mass of Na₂SO₄.

Step-by-step explanation:

The student is asking how many grams of sodium sulfate (Na₂SO₄) are needed to prepare a 1.2-liter solution with a normality of 0.5 N. To answer this question, we must first understand the relationship between normality (N) and molarity (M). Normality is the number of equivalents of solute per liter of solution, and for Na₂SO₄, the number of equivalents equals its valency, which is 2 (since SO₄ has a -2 charge).

First, we need to determine the molarity (M):

1. 0.5 N solution of Na₂SO₄ will have a molarity of 0.25 M because 0.5 N * (1 equivalent/2) = 0.25 M
2. Then, calculate the number of moles: Molarity (M) = moles/volume (L), so moles = Molarity * Volume = 0.25 mol/L * 1.2 L = 0.3 moles of Na₂SO₄
3. Finally, calculate the mass: mass = moles * molar mass. The molar mass of Na₂SO₄ is 142 g/mol. Therefore, the mass required = 0.3 moles * 142 g/mol = 42.6 grams of Na₂SO₄.