Molarity & Solution Concentration Calculator
Calculate solution concentration (molarity), find moles of solute, mass needed to make a solution, or volume required. Essential for lab work and A-level chemistry.
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Solution Concentration Guide
What do I need to know about 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.
What's the key thing to understand about 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 rather than making up to the mark by eye (this overshoots or undershoots the true volume), reading the meniscus from above or below eye level (parallax error), and not rinsing the weighing vessel or funnel fully when transferring the solid or concentrated solution into the flask, which leaves some of the solute behind and gives a solution more dilute than intended.
What do I need to know about 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.
What should I know about 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.