What is Molarity (Concentration)?
Molarity is the most common way chemists express concentration — how much solute is dissolved in a given volume of solution. It links the amount of substance (moles) directly to the space it occupies in solution.
Molarity is calculated as M = n/V, where n is the moles of solute and V is the volume of solution in liters; its unit is mol/L, also written as M.
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Step-by-step worked examples
0.5 mol of NaCl is dissolved to make 2 L of solution. Find the molarity.
M = n/V M = 0.5/2 M = 0.25 mol/L
How many moles of solute are needed to make 3 L of a 1.5 M solution?
M = n/V → n = M × V n = 1.5 × 3 n = 4.5 mol
2 mol of HCl is dissolved in enough water to give a concentration of 4 M. Find the volume of solution.
M = n/V → V = n/M V = 2/4 V = 0.5 L
Flashcards
Quick quiz
Q1.What is the molarity of a solution with 3 mol of solute in 6 L?
Q2.A solution's molarity increases when…
Q3.How many moles are in 2 L of a 3 M solution?
Q4.What happens to molarity when you dilute a solution with water?
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Common mistakes
Using volume of solvent instead of total volume of solution. — Correct: V in M = n/V is the total volume of the solution, not just the solvent added.
Forgetting to convert grams of solute into moles first. — Correct: Divide mass by molar mass to get n before applying M = n/V.
Confusing molarity (mol/L) with molality (mol/kg). — Correct: Molarity uses volume of solution; molality uses mass of solvent — they're different quantities.
Assuming mixing two solutions doubles the molarity. — Correct: Mixing dilutes both solutions — use conservation of moles (M₁V₁ + M₂V₂ = M_final × V_total) instead.
FAQ
What is molarity?
Molarity is a measure of concentration equal to the moles of solute dissolved per liter of solution, written M = n/V.
What is the molarity formula?
M = n/V, where M is molarity (mol/L), n is moles of solute, and V is the volume of solution in liters.
What are examples of molarity?
Dissolving 1 mole of NaCl in 1 liter of water gives a 1 M solution; diluting it to 2 liters gives a 0.5 M solution.
How do you calculate molarity?
Divide the moles of solute by the volume of the solution in liters: M = n/V.