Molarity Calculator

In short Molarity is moles of solute per litre of solution, and every molarity question is the same three-way relationship: moles equals mass divided by molar mass, and molarity equals moles divided by volume in litres. Give any two and the third follows. Weighing 5.844 g of sodium chloride, molar mass 58.44 g/mol, gives 0.1 mol; dissolving that and making it up to 100 mL gives exactly 1.000 M. The detail that trips people up is the word solution. Molarity is per litre of finished solution, not per litre of solvent — you dissolve the solid first and then make the volume up to the mark. Adding a solid to a litre of water gives more than a litre of solution and therefore a lower concentration than you intended, and for a concentrated solution the error is large enough to matter. The second detail is that molarity is temperature-dependent, because volume is. The same flask holds fewer moles per litre when it is warm, so where precision matters over a temperature range chemists use molality — moles per kilogram of solvent — because a kilogram stays a kilogram whatever the temperature. A useful shortcut for converting units: a solution's concentration in mg/mL is molarity multiplied by molar mass, and mg/mL and g/L are the same number, so a 1.000 M sodium chloride solution is 58.44 g/L.