Molarity Calculator

Three ways round the same relationship: find the molarity from a mass and a volume, the mass you need for a target concentration and volume, or the volume that a given mass will make up to a given concentration. Mass takes mg, g or kg, volume takes mL or L, concentration takes mM or M, and the molar mass defaults to 58.44 g/mol, which is sodium chloride — so the starting figures, 5.844 g made up to 1 L, describe a 0.1 M saline.

The arithmetic is three lines long; what the arithmetic cannot tell you is the part that ruins solutions. Molarity is moles per litre of solution, not per litre of solvent — and the distinction is the whole game. Adding 1 mol of solute to 1 L of water does not give you 1 M, because the solute takes up room of its own — you dissolve it in less water and then bring the total up to the mark in a volumetric flask. The tool's volume field means final volume throughout, and if you read it as "water added" every result is quietly too dilute.

Two more traps sit in the molar mass rather than the volume. It has to match the form you are actually weighing: copper(II) sulfate is 159.60 g/mol anhydrous but 249.68 as the familiar blue pentahydrate, so weighing the pentahydrate against the anhydrous figure leaves you at 63.9% of the concentration you wanted. And because molarity is defined per unit volume, it drifts with temperature while the mass does not — water is about 2.6% less dense at 80 °C than at 20 °C, so a solution made up to 1.000 M on the bench reads near 0.974 M once it is hot. Where that matters, molality, in moles per kilogram of solvent, is the quantity that holds still.