Molarity Calculator
Calculate molarity, moles, or volume of solutions using M = n/V formula.
Formula: M = n / V
What Is the Molarity Calculator?
The Molarity Calculator computes the molar concentration (molarity) of a solution from the mass of solute dissolved, the molar mass of the substance, and the total volume of solution. It also calculates how much solute to weigh to prepare a solution of target molarity and volume.
Formula
How to Use
Enter the mass of solute (grams), the molar mass of the compound (g/mol — from formula weight), and the volume of solution (liters or milliliters). The calculator outputs molarity in mol/L (M). To find mass needed: enter target molarity, volume, and molar mass.
Example Calculation
Dissolve 58.44g of NaCl (molar mass=58.44 g/mol) in 1 liter of water: Moles = 58.44÷58.44 = 1 mol. Molarity = 1 mol÷1 L = 1 M NaCl. To make 500 mL of 0.5M glucose (MW=180.16): Mass = 0.5×0.500×180.16 = 45.04g glucose.
Understanding Molarity
Molarity is the most fundamental concentration unit in chemistry, defining the amount of dissolved substance per unit volume of solution. Expressed in moles per liter (mol/L or M), it allows chemists to work with stoichiometric amounts precisely — essential for reaction yield calculations, dilution planning, titration analysis, and solution preparation.
Preparing a solution of known molarity requires two key pieces of information: the number of moles needed (= molarity × volume) and the molar mass of the solute (converting moles to grams for weighing). The process: calculate mass needed, weigh it accurately on an analytical balance, dissolve in a small amount of solvent, transfer to a volumetric flask, and add solvent to exactly the target volume.
Molarity is used universally in quantitative chemistry: acid-base titrations (standardized HCl and NaOH solutions), spectrophotometric assays (Beer-Lambert law uses molar concentration), enzyme kinetics (Km and Vmax expressed in molarity), electrochemistry (Nernst equation uses concentration), and pharmaceutical preparation (drug concentration in IV solutions and oral medications). Accurate molarity calculations are critical for reproducibility and safety in laboratory practice.
Frequently Asked Questions
What is the difference between molarity, molality, and normality?
Molarity (M) = moles/liter of solution. Molality (m) = moles/kilogram of solvent (not solution). Normality (N) = equivalents/liter, depending on the reaction type. Molarity is the most commonly used concentration unit in chemistry.
Why is molar mass important?
Molar mass (g/mol) converts between grams (what you weigh) and moles (what equations use). It is the sum of atomic masses from the periodic table. For NaCl: Na(23) + Cl(35.45) = 58.45 g/mol.
What does 1 M mean?
1 molar (1 M) means 1 mole of solute per liter of solution. 1 mole ≈ 6.022×10²³ molecules. For water, 1 liter weighs about 1 kg, but for solutions with dense solutes, 1 liter of solution weighs more.
What is a standard solution?
A standard solution is a precisely known concentration, used for calibration and titrations. Primary standards (high purity, stable solids) are weighed accurately and dissolved to prepare standard solutions of exact molarity.
Is this calculator free?
Yes, completely free with no registration required.
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