How to prepare a molar solution from a solid
A step by step guide to weighing out a solute, dissolving it, and topping up to the mark so your solution hits the target molarity.
Start from the concentration you need
Preparing a solution begins with the target molarity and the final volume you want to make. Multiply the molarity by the volume in litres to get the moles of solute required, then multiply those moles by the molar mass to get a mass in grams to weigh out. For example, one litre of 1 M sodium chloride needs one mole, and since the molar mass is 58.44 g/mol you weigh 58.44 grams. This calculator does the first two steps for you when you solve for moles or enter mass and molar mass.
Weigh, dissolve, then dilute to volume
Accurately weigh the solid on a balance and transfer it into a volumetric flask that matches your final volume. Add a portion of solvent and swirl until the solid fully dissolves, because adding all the water first leaves less room to mix. Once dissolved, top the flask up to the calibrated line, which fixes the total solution volume and therefore the molarity. Filling to the mark, rather than measuring the solvent separately, is what makes molarity accurate.
Why final volume, not solvent volume, matters
Molarity is defined per litre of solution, so the number that counts is the volume after the solute has dissolved, not the volume of water you poured in. Dissolving a solid can change the total volume slightly, and for concentrated solutions the difference is real. That is why laboratory recipes always say to dissolve and then dilute to a set volume in a volumetric flask. Skipping the flask and simply adding a litre of water to the powder gives a slightly weaker solution than intended.
Checking your result
After making the solution you can verify it by plugging the actual mass, molar mass and volume back into the calculator to confirm the molarity landed where you expected. If the number is off, the usual culprits are a weighing error, an unaccounted hydrate in the salt, or measuring solvent instead of final volume. Keeping the molar mass value handy and rechecking it against the compound formula catches most mistakes before they reach the bench.