⚗ Molarity Calculator
Calculate molar concentration (molarity), moles of solute, or volume of solution. Essential for chemistry labs and solution preparation.
Molarity (M) measures how many moles of solute are dissolved in one litre of solution. It is the most commonly used concentration unit in chemistry.
How to use this calculator: Enter any two values (moles, volume, or molarity) and click Calculate. The calculator will solve for the missing value using M = n / V (n = moles, V = litres).
Example: To prepare 500 mL (0.5 L) of 0.1 M NaCl: required moles = M × V = 0.1 × 0.5 = 0.05 mol. Convert moles to mass using molar mass (NaCl ? 58.44 g/mol): mass = 0.05 × 58.44 ? 2.922 g NaCl.
Dilution: Use the dilution equation M1 × V1 = M2 × V2 to calculate how much stock solution to dilute to obtain a desired concentration.
Units & conversions: Molarity is expressed in mol·L?1 (mol/L). To convert grams to moles: moles = mass (g) / molar mass (g·mol?1). For many lab tasks you will also need the molar mass of the solute.
Practical tips: Molarity depends on solution volume, which changes with temperature. For accurate work use volumetric flasks and record the temperature. When preparing solutions, add solute to solvent and mix; for acids, always add acid to water slowly and with cooling.
📊 Common Solution Concentrations
| Solution | Molarity | Use |
|---|---|---|
| Saline (0.9% NaCl) | 0.154 M | IV fluids, eye drops |
| HCl (stomach acid) | 0.1 M | Digestive acid |
| Vinegar (acetic acid) | 0.83 M | Food, cleaning |
| Seawater (NaCl) | ~0.6 M | Marine biology |
🔗 Related Calculators
Molarity and Solution Concentration Explained
Molarity (M) is the most common way to express solution concentration in chemistry: Molarity = Moles of Solute ÷ Liters of Solution. A 1 M (1 molar) solution contains 1 mole of solute per liter of solution. For example, a 1 M NaCl solution contains 58.44 g of sodium chloride per liter (since the molar mass of NaCl is 58.44 g/mol).
Moles, Molar Mass, and Avogadro's Number
A mole is 6.022 × 10²³ particles (Avogadro's number) — an enormous number chosen so that 1 mole of any element has a mass in grams equal to its atomic mass. Carbon has an atomic mass of 12 u, so 1 mole of carbon weighs exactly 12 grams. This relationship makes stoichiometry calculations practical: weigh out 12g of carbon and you have exactly 6.022 × 10²³ carbon atoms.
Dilution Calculations: C₁V₁ = C₂V₂
When you dilute a solution, the amount of solute stays constant even as the volume increases. The dilution formula is: C₁V₁ = C₂V₂ (initial concentration × initial volume = final concentration × final volume). To make 500 mL of 0.1 M HCl from 1 M HCl stock: 1 M × V₁ = 0.1 M × 0.5 L → V₁ = 0.05 L = 50 mL. Add 50 mL of 1 M HCl to enough water to make 500 mL total.
Understanding Molarity and Concentration
Molarity (M) measures the concentration of a solution: M = moles of solute ÷ liters of solution. A 1 M (1 molar) solution of NaCl contains 1 mole (58.44 grams) of sodium chloride per liter of solution. To find moles from grams: moles = grams ÷ molar mass. Molar mass is found by summing the atomic masses of all atoms in the molecule from the periodic table (H = 1.008, C = 12.011, N = 14.007, O = 15.999, Na = 22.990, Cl = 35.453, etc.). For glucose (C₆H₁₂O₆): molar mass = 6(12.011) + 12(1.008) + 6(15.999) = 72.066 + 12.096 + 95.994 = 180.156 g/mol. A 0.5 M glucose solution contains 180.156 × 0.5 = 90.08 g of glucose per liter.
Dilution Calculations
When diluting a solution, the number of moles of solute stays constant while the volume increases. The dilution formula is: C₁V₁ = C₂V₂ (initial concentration × initial volume = final concentration × final volume). To make 500 mL of 0.1 M HCl from a 12 M concentrated stock: V₁ = (0.1 × 0.500) ÷ 12 = 0.00417 L = 4.17 mL. Add 4.17 mL of concentrated HCl to enough water to make 500 mL total (always add acid to water, never water to acid — it's safer). In laboratory practice, always use volumetric flasks for precise concentration preparation, not graduated cylinders. Pipettes should be used to measure small volumes of concentrated stock solutions accurately.
Molarity in Everyday Chemistry and Medicine
Molarity appears throughout practical chemistry and medicine. IV fluids: normal saline (0.9% NaCl) has a concentration of 0.154 M — chosen to match blood plasma osmolarity (~308 mOsm/L). Dextrose 5% in water (D5W) is 0.278 M glucose. Blood chemistry: blood glucose is typically reported in mg/dL (US) or mmol/L (most of the world). Normal fasting glucose is 70–100 mg/dL or 3.9–5.6 mmol/L. Acids and bases: household vinegar is approximately 0.8 M acetic acid; stomach acid (HCl) is about 0.1 M; a pH 7 solution has [H⁺] = 10⁻⁷ M = 0.0000001 M. Drug dosing: intravenous medications are prepared in molar concentrations to ensure precise dosing by volume.
