Molarity of common concentrated solutions
Lab solutions are often purchased as concentrated solutions of a standard strength. This strength is often given as a percentage (e.g. w/w) however it is usually more convenient to know these as molarity. The calculations are simple enough but are tedious and require knowledge of the density of the solution as well as molecular mass of the molecule.
This list includes commonly used commercially available solutions and their molar equivalent.
- Glacial acetic acid - 17.47M
- 98-100% formic acid (density = 1.22 g/cm³) - 26.51M
- 70% perchloric acid (density = 1.664 g/cm³) - 11.65M
- 60% perchloric acid (density = 1.535 g/cm³) - 9.17M
- 35% NH3OH (ammonium hydroxide) (by mass) - 18.08M
- 70% HNO3 (nitric acid) (density = 1.4 g/cm³) - 17.46M
- 32% HCl (hydrochloric acid) (density = 1.159 g/cm³) - 10.17M
- 38% HCl (hydrochloric acid) (density = 1.189 g/cm³) - 12.39M
This is an example calculation for perchloric acid (HClO4; molar mass = 100.46 g/mol) which is commonly provided commercially as a 70% w/w solution with a density of 1.664 g/cm³.
1 L x density (1.664 g/cm³) = 1.664 kg
1.664 kg x 0.7 (w/w percentage of PCA) = 1.165 kg PCA/L
1165 g PCA / molar mass of PCA (100.46 g/mol) = 11.6 Molar
First published on 30th May 2011 and last modified on 19th May 2013.