Concentration Calculator

Molarity (M) is the number of moles of solute per liter of solution. Molarity = moles / liters. To prepare a 1.0 M solution of NaCl, dissolve 58.44 g (1 mole) of NaCl in water and bring the total volume to 1.000 L. Molarity is the most common concentration unit in chemistry labs.

Molarity (mol/L) is moles per liter of solution - it changes with temperature because liquid volume expands. Molality (mol/kg) is moles per kilogram of solvent - it does not change with temperature. Molality is used for colligative properties (boiling point elevation, freezing point depression) because it is temperature-independent.

To convert molarity to g/L: multiply by molar mass (M x g/mol = g/L). To convert g/L to molarity: divide by molar mass. To convert to ppm (mg/L for dilute aqueous solutions): 1 ppm = 1 mg/L = 0.001 g/L. For w/w%: %(w/w) = (g solute / g solution) x 100. The w/w mode here asks for the mass of solute and the mass of solution in grams directly (not a density); to then turn that percentage into molarity you additionally need the solution density, which converts the solution mass into a volume.

For dilute aqueous solutions ppm and mg/L are the same thing: 1 ppm = 1 mg of solute per liter of solution. Compute mg/L by dividing the solute mass in milligrams by the solution volume in liters (mg/L = mg / L). From g/L, multiply by 1000: 1 g/L = 1000 mg/L = 1000 ppm. From molarity, ppm = molarity (mol/L) x molar mass (g/mol) x 1000. Example: a 0.001 M solution of a 60 g/mol compound is 0.001 x 60 x 1000 = 60 ppm.