Molarity Calculator

About the Molarity Calculator

A molarity calculator computes solution concentration (molarity, M), moles of solute, mass of solute, or volume of solution when three of the four quantities are known. Molarity — moles of solute per litre of solution — is the most widely used concentration unit in chemistry because it directly relates to stoichiometry: equal volumes of equimolar solutions contain equal numbers of molecules, enabling straightforward reaction calculations. The core formula is M = n/V = (mass/MW)/V_litres, where n is moles of solute and V is the solution volume in litres. Laboratory solution preparation, titration analysis, pharmaceutical formulation, industrial chemical processes, and academic chemistry homework all depend on accurate molarity calculations. Common examples: preparing 1 L of 0.1 M NaOH (dissolve 4.00 g NaOH per litre), performing an acid-base titration, or calculating the concentration of a commercial reagent after dilution. Used by chemistry students, laboratory technicians, pharmacists, and chemical engineers worldwide.

How It Works

M = n / V_L = (mass / MW) / V_L. Rearrangements: mass = M × V_L × MW; moles = M × V_L; V_L = moles / M = mass / (M × MW). Dilution: M₁V₁ = M₂V₂ (moles are conserved on dilution). Step-by-step to make 250 mL of 0.5 M glucose solution: MW of glucose (C₆H₁₂O₆) = 180.16 g/mol. Moles needed = 0.5 × 0.250 = 0.125 mol. Mass needed = 0.125 × 180.16 = 22.52 g. Dissolve 22.52 g glucose in water and make up to exactly 250 mL in a volumetric flask. For dilutions: to make 500 mL of 0.1 M HCl from 6 M stock: V₁ = M₂V₂/M₁ = (0.1 × 0.5) / 6 = 0.00833 L = 8.33 mL. Add 8.33 mL stock to ~450 mL water, mix, make up to 500 mL.

Tips & Best Practices

• ✓Always add concentrated acid or base to water — never water to concentrated acid. The heat of dilution can cause violent spattering if water is added to a concentrated acid. This is standard laboratory safety practice (ASAW: Always Slowly Add to Water).
• ✓Use volumetric flasks for accurate solution preparation. A volumetric flask has a single calibration mark at the neck for exact volume at a specified temperature (usually 20°C). Beakers and graduated cylinders are not accurate enough for analytical work — they have ±5% tolerance vs ±0.1% for a class A volumetric flask.
• ✓Molarity vs molality: molarity (M) uses solution volume as denominator and changes with temperature; molality (m) uses solvent mass and is temperature-independent. For precise work at varying temperatures (cryoscopy, osmometry, colligative properties), molality is preferred.
• ✓Commercially supplied reagents have labelled concentrations and densities. To find molarity from "% w/w" (weight percent): M = (% × 10 × density) / MW. Example: 37% HCl, density 1.19 g/mL, MW 36.46: M = (37 × 10 × 1.19) / 36.46 = 12.1 mol/L.

Who Uses This Calculator

Chemistry students and teachers preparing for and running titration experiments and quantitative analysis. Laboratory technicians preparing standard solutions and calibration standards. Pharmaceutical formulators calculating drug concentrations in preparations. Industrial chemists designing reaction mixtures and calculating reagent requirements for scale-up.