What is the molarity of a solution that has 525 grams of sodium chloride (NaCl) in 800 mL of water?

Answer 1

Since molarity is defined as moles of solute per liter of solution, we need to find both values.

moles solute = 525 g NaCl x 1 mol NaCl / 58.4 g = 8.9897 mols

volume in liters = 800 ml x 1 L / 1000 ml = 0.800 L (assuming the volume didn't change when adding NaCl which is not a valid assumption - see below).

Molarity = 8.9897 mols / 0.800 L = 11.24 M = 11.2 M (3 sig. figs.)

NOTE: since molarity is based on 1 liter of solution, not 1 liter of added solvent, you'd have to assume that the final volume of solution is 800 ml and that the 525 g of NaCl didn't increase the volume. This is not the case, so this answer is just an exercise and not a valid response.

Perhaps, you wanted to know the molality which is moles solute per kg of solvent. In that case, we have...

8.9897 mols solute

0.800 kg of solute (assuming a density of 1g/ml for water)

m = molality = 11.2 m