MOLARITY www.chemistry-dictionary.com C H E M I S T R Y- D I C T I O N A R Y. C O M · E X P L A I N E R How Molarity Works You dissolved the solid in exactly one litre of water, and your solution is still not 1 M. That one detail costs more marks than any other part of this topic. Molarity counts moles per litre of finished solution, not per litre of the water you started with. The solid takes up room once it dissolves, so the water you poured in and the solution you ended up with are two different volumes. That is why a volumetric flask has a line on its neck instead of markings up the side. You dissolve first, then top up to the line. Once that clicks, molarity stops being a formula to memorise and becomes an exchange rate. Volume is the thing you can measure in a lab. Moles are the thing a chemical equation actually wants. Molarity is what converts between them. Here is the mental model you should have: Molarity is a ratio, not an amount. It tells you how crowded the solute is, not how much of it you own The formula is moles of solute divided by litres of solution, and the units are mol per litre, written M Grams mean nothing to that formula. Divide by molar mass first to turn them into moles Sodium chloride has a molar mass of 58.44 grams per mole, so 58.44 grams made up to 1.000 litres is 1.00 M The volume on the bottom of that fraction is always the final solution, measured to the mark Multiply molarity by volume in litres and you get moles, which is the number a balanced equation needs Diluting adds volume but adds no moles, which is the whole reason M1V1 equals M2V2 Millilitres are not litres. Divide by 1000 before that number goes anywhere near the formula The common mistake is not the algebra. Most students can rearrange the formula fine. They lose the marks by feeding the wrong volume into it, or by leaving millilitres in place and being wrong by a factor of a thousand without noticing, because the answer still looks like a number. The second mistake is treating a concentration like a quantity. A drop of 12 M acid contains far fewer moles than a bucket of 0.1 M acid. Concentration alone never tells you how much is there. You need the volume as well. Chemists read a pipette as a counting device. When they draw 25.0 mL from a bottle labelled 0.100 M, they are not thinking about liquid. They are thinking that they have just counted out 0.00250 moles of something, and that number is what goes into the equation. The glassware is only there to make the count trustworthy. If someone handed you a bottle labelled 0.100 M and a 25.0 mL pipette right now, could you say how many moles you had just delivered without reaching for a calculator? Molarity calculator with the working shown: https://www.chemistry-dictionary.com/tools/molarity-calculator/ Full definition: https://www.chemistry-dictionary.com/molarity/