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About This Calculator
Molarity measures the concentration of a solute dissolved in a solution, expressed in moles per liter. This calculator helps chemists and students determine how much solute is needed to prepare a solution of a specific concentration. Understanding molarity is fundamental to stoichiometry, titration experiments, and pharmaceutical formulations.
Quick Tips
- 1 Divide solute grams by molar mass, then divide by solution liters.
- 2 Dilution follows C1V1 = C2V2, making concentration changes easy to calculate.
- 3 Always add solute to solvent, never the reverse, for accurate molar solutions.
Example Calculation
58.44g NaCl (molar mass 58.44 g/mol) dissolved in 2 liters of water.
Moles: 1.0 mol | Molarity: 0.5 M | Concentration: 0.5 mol/L
What Is Molarity?
Molarity (M) is the number of moles of solute per liter of solution. It is the most common way to express concentration in chemistry. A 1 M solution contains 1 mole of solute in 1 liter of total solution.
How to Calculate Molarity
Molarity = moles of solute / volume of solution in liters. To find moles from mass, divide the mass in grams by the molar mass (g/mol) from the periodic table. Then divide by the volume to get molarity.
Molarity vs Molality
Molarity (M) uses liters of solution, while molality (m) uses kilograms of solvent. Molality does not change with temperature because mass is constant, while molarity changes as liquid volume expands or contracts with temperature.
Dilution Calculations
When diluting a solution, use M1V1 = M2V2. If you have 100 mL of 2 M solution and add water to make 500 mL, the new molarity is (2 x 0.1) / 0.5 = 0.4 M. This formula is essential for laboratory preparation.
Frequently Asked Questions
Molarity (M) is moles per liter of solution. Molality (m) is moles per kilogram of solvent. Molality is preferred for precise work because it does not change with temperature, while molarity does as the solution volume changes.
Divide the mass in grams by the molar mass of the substance. The molar mass is found on the periodic table. For example, NaCl has a molar mass of 58.44 g/mol, so 29.22 grams equals 0.5 moles.
Normality (N) equals molarity multiplied by the number of equivalents. For acids, the number of equivalents is the number of ionizable hydrogens. A 1 M H2SO4 solution is 2 N because sulfuric acid has two ionizable hydrogens.
Molarity is used to prepare solutions of known concentration, calculate reaction stoichiometry, perform titrations, and standardize reagents. Most chemical reactions in solution require knowing the molarity of the reactants.