Fill in any three of mass, molecular weight, volume and concentration to find the fourth, and see the moles of solute too.
Molarity = mass ÷ (molecular weight × volume). Leave blank the one box you want to find. The default finds the concentration of 100 g of table salt in 2 L.
Molarity, also called molar concentration, is the number of moles of a dissolved substance in each liter of solution. It is written as M, so a 2 M solution has 2 moles per liter. It is the usual way to describe the strength of a solution in a laboratory, in pharmacy and in industry. The formula is M = n ÷ V, where n is the amount of solute in moles and V is the volume of the solution in liters.
You often know the mass of the solute and not the number of moles. Divide the mass by the molecular weight, which is the mass of one mole in grams per mole, to get the moles. So molarity = mass ÷ (molecular weight × volume). For 100 g of sodium chloride, which has a molecular weight of 58.44 g/mol, in 2 liters of solution, there are 1.711 moles, and the molarity is 0.8556 M. The calculator uses the term molecular weight as it is used for molar mass in g/mol.
Rearrange the same equation to find any of the four values. The mass is volume × molarity × molecular weight. The volume is mass ÷ (molecular weight × molarity). The molecular weight is mass ÷ (volume × molarity). If you give the concentration as a mass concentration, such as g/L, the mass and volume can be found without the molecular weight, but the molecular weight itself cannot, because mass divided by volume already is the concentration.
Molar units are M, mM, μM, nM and mol/m³. Mass units are kg/L, g/L, mg/L, kg/m³ and g/m³. The units ppm and ppb are treated as mg/L and μg/L, which holds for dilute solutions in water, where one liter has a mass of about one kilogram. Volume units include liters, milliliters, US gallons, quarts, pints, cups and fluid ounces, and mass units reach from micrograms to metric tons, pounds, ounces and atomic mass units.
Divide the moles of solute by the volume of the solution in liters. If you know the mass, first divide it by the molecular weight to get the moles.
The molecular weight of NaCl is 58.44 g/mol, so 58.44 g is 1 mole, and 1 mole in 1 liter is a 1 M solution.
Molarity is moles per liter of solution. Molality is moles per kilogram of solvent. Molarity changes with temperature because the volume does, and molality does not.
For a dilute water solution, 1 ppm is 1 mg per liter. Divide the milligrams per liter by 1,000 to get grams per liter, then divide by the molecular weight to get molarity.
A concentration in g/L is already mass over volume, so it carries no information about how many moles the mass contains. You need a molar concentration to find the molecular weight.
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