Concentration Calculator
Calculate molarity, solve dilution problems, and find percent composition, with step-by-step solutions.
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Molarity (M = mol / L)
How It Works
Concentration describes how much solute is dissolved in a given amount of solution. The most common unit in chemistry is molarity (M), defined as moles of solute per liter of solution. To calculate molarity you need the mass of solute, its molar mass, and the solution volume.
The dilution equation C₁V₁ = C₂V₂ relates the concentration and volume before and after a dilution of the same solute. It applies when solvent is added without reaction or solute loss, so the moles of solute stay constant. Use consistent volume units. Given any three of the four values, this calculator solves for the fourth.
Mass percent (w/w) expresses concentration as the mass of solute divided by the total mass of solution, multiplied by 100. It's commonly used in pharmacy, food science, and material preparation where volume measurements are impractical.
All three modes show the complete working so you can follow the algebra and check your homework. The molarity mode can auto-calculate molar mass from a chemical formula, saving you a separate calculation step.
Reference: OpenStax Chemistry 2e, Molarity.
Frequently Asked Questions
What is molarity?
Molarity (M) is the concentration of a solution expressed as moles of solute per liter of solution. A 1 M solution contains one mole of solute dissolved in enough solvent to make one liter of solution.
How do you calculate molarity?
Divide the moles of solute by the volume of solution in liters (M = mol ÷ L). To get moles from a mass, divide the mass in grams by the solute’s molar mass.
How does the dilution equation C₁V₁ = C₂V₂ work?
Adding solvent does not change the number of moles of solute, so the product of concentration and volume stays constant before and after dilution. Given any three of the four quantities, solve for the fourth.
What is the difference between molarity and molality?
Molarity is moles of solute per liter of solution (mol/L); molality is moles of solute per kilogram of solvent (mol/kg). Molality is preferred when temperature changes, because mass does not vary with temperature the way volume does.
What is mass percent concentration?
Mass percent (% w/w) is the mass of solute divided by the total mass of solution, times 100. For example, 10 g of salt in 200 g of solution is 5% by mass.