What is the molarity of a solution containing 100 g NaCl dissolved in 1 liter of solution? (MW ≈ 58 g/mol)

• A. 1.72 M
• B. 3.45 M
• C. 0.86 M
• D. 29 M

Answer: (A)

Molarity measures how many moles of solute are in each liter of solution. To find it, convert the mass of solute to moles using the molar mass: 100 g NaCl ÷ 58 g/mol ≈ 1.72 mol. With a total solution volume of 1 liter, the molarity is 1.72 mol per liter, or about 1.72 M. Remember, NaCl’s dissociation into Na+ and Cl− in water doesn’t change the amount of NaCl you dissolved, which is what molarity reflects. If the volume were different, the molarity would change inversely with the volume.