What is the molarity of a solution containing 50 g NaCl in 1 L of solution? (MW ≈ 58 g/mol)

• A. 0.86 M
• B. 1.72 M
• C. 3.45 M
• D. 0.045 M

Answer: (A)

Molarity is the number of moles of solute per liter of solution. Convert the mass of NaCl to moles using its molar mass (about 58 g per mole): 50 g ÷ 58 g/mol ≈ 0.862 mol. With 1 liter of solution, the molarity is 0.862 mol / 1 L ≈ 0.86 M. So the solution is about 0.86 M.

If you check the other numbers, they would come from using more or less NaCl per liter (for example, ~100 g per liter gives ~1.72 M, ~200 g per liter gives ~3.45 M, and ~2.6 g per liter gives ~0.045 M).