Molarity & Solution Concentration Calculator

Solution Concentration Guide

The Molarity Formula

Molarity (c) = moles of solute (n) ÷ volume of solution in litres (V). Unit: mol/L (also written as M). Example: dissolve 0.1 mol NaCl in 250 mL water → c = 0.1 ÷ 0.25 = 0.4 mol/L. Note: volume is the final solution volume, not the volume of water added. When making a solution, add solute to some water, dissolve, then make up to the required volume using a volumetric flask.

Making Standard Solutions

To make a solution of known concentration: calculate the mass needed = moles × molar mass. Weigh accurately on a 4-decimal place balance. Dissolve in a small volume of distilled water in a beaker with stirring. Transfer quantitatively to a volumetric flask of the required volume. Rinse the beaker 3 times with distilled water, adding rinsings to the flask. Make up to the graduation mark (bottom of meniscus on the line). Stopper and invert 10 times to mix. Common errors: measuring water volume rat

Dilution Calculations

The dilution formula: c₁V₁ = c₂V₂. Where c₁ = initial concentration, V₁ = volume of stock solution taken, c₂ = required final concentration, V₂ = required final volume. Example: make 100 mL of 0.1 mol/L HCl from 2.0 mol/L stock: V₁ = (0.1 × 100) ÷ 2.0 = 5 mL. Take 5 mL of stock acid and make up to 100 mL total volume. Serial dilution: diluting in stages (e.g., 1:10 three times = 1:1000 overall) — used when a single dilution would be impractical or inaccurate.

Concentration Units Beyond Molarity

Molarity (M or mol/L): moles per litre of solution. Most common in chemistry. Molality (m or mol/kg): moles per kilogram of solvent. Used when temperature changes matter (density-independent). Mass concentration (g/L): mass of solute per litre. Used in biology and medicine. Percent concentration: % w/v (g/100 mL), % w/w (g/100 g), % v/v (mL/100 mL). Conversion between these requires density data. For most GCSE and A-level chemistry: mol/L is the standard unit.