Molarity Calculator – Calculate Molar Concentration Instantly
Use our free molarity calculator to find the molar concentration of a solution. Enter moles of solute and volume of solution to get accurate results in seconds. Perfect for chemistry students, lab technicians, and researchers.
Molarity tells you how concentrated a solution is. Specifically, it's the number of moles of solute dissolved in one liter of solution. The symbol is M (capital M), and you'll see it written as "2 M NaCl" or "0.1 M HCl" on lab bottles.
One mole equals 6.022 × 10²³ particles (Avogadro's number). So a 1 M solution contains 6.022 × 10²³ molecules of solute per liter. This seems abstract, but it's practical: equal volumes of solutions with the same molarity contain the same number of molecules, regardless of what those molecules are.
The Molarity Formula
M = n / V
M = molarity (mol/L), n = moles of solute, V = volume in liters
Important distinction: molarity uses the volume of the final solution, not the volume of solvent you started with. If you dissolve salt in 1 L of water, the final volume exceeds 1 L. Always measure the final solution volume for accurate molarity.
Example 1: Finding Molarity
Problem: You dissolve 0.5 moles of NaCl in enough water to make 500 mL of solution. What's the molarity?
Given: n = 0.5 mol, V = 500 mL = 0.5 L
M = n / V = 0.5 mol / 0.5 L = 1.0 M
Answer: The solution is 1.0 M NaCl
Example 2: Finding Moles
Problem: How many moles of HCl are in 250 mL of 2.0 M HCl solution?
Given: M = 2.0 mol/L, V = 250 mL = 0.25 L
n = M × V = 2.0 mol/L × 0.25 L = 0.5 mol
Answer: The solution contains 0.5 moles of HCl
Example 3: Finding Volume
Problem: What volume of 1.5 M NaOH contains 0.3 moles of NaOH?
Given: n = 0.3 mol, M = 1.5 mol/L
V = n / M = 0.3 mol / 1.5 mol/L = 0.2 L = 200 mL
Answer: You need 200 mL of the solution
| Moles (mol) | Volume (mL) | Molarity (M) | Common Use |
|---|---|---|---|
| 0.1 | 100 | 1.0 | Standard titration |
| 0.5 | 500 | 1.0 | General lab work |
| 1.0 | 1000 | 1.0 | Stock solution |
| 0.25 | 250 | 1.0 | Standard solution |
| 2.0 | 500 | 4.0 | Concentrated reagent |
| 0.01 | 100 | 0.1 | Dilute standard |
| Unit | Formula | Temperature Dependent | Best For |
|---|---|---|---|
| Molarity (M) | mol solute / L solution | Yes | General lab work, titrations |
| Molality (m) | mol solute / kg solvent | No | Colligative properties, precise work |
| Normality (N) | equivalents / L solution | Yes | Acid-base, redox reactions |
| Mass % | (g solute / g solution) × 100 | No | Industrial applications |
| ppm | mg solute / L solution | Yes | Trace analysis, environmental |
Molarity changes with temperature because volume expands/contracts. Molality stays constant because mass doesn't change with temperature. For precise thermodynamic work, use molality.
How do I convert grams to moles for molarity?
Divide grams by molar mass. For NaCl: molar mass = 58.44 g/mol. So 29.22 g NaCl = 29.22 / 58.44 = 0.5 mol. Then use M = n/V. If dissolved in 500 mL: M = 0.5 mol / 0.5 L = 1.0 M.
What's the difference between 1 M and 1 m?
1 M (molar) = 1 mole per liter of solution. 1 m (molal) = 1 mole per kilogram of solvent. For dilute aqueous solutions, they're nearly equal. For concentrated solutions or non-aqueous solvents, they differ significantly.
How do I prepare a molar solution?
Weigh the required moles of solute. Add to a volumetric flask. Add solvent to about 3/4 full and swirl to dissolve. Then add solvent to the calibration mark. Never add solute directly to a full-volume flask – it won't dissolve properly.
Can molarity be greater than 10 M?
Yes. Concentrated HCl is about 12 M. Concentrated H₂SO₄ is about 18 M. Concentrated NaOH can reach 19 M. These are limited by solubility – eventually, no more solute will dissolve regardless of how much you add.
How do I dilute a solution to a specific molarity?
Use M₁V₁ = M₂V₂. Want 500 mL of 0.1 M from 1.0 M stock? (1.0)(V₁) = (0.1)(500), so V₁ = 50 mL. Take 50 mL of stock, add water to 500 mL total. Always add acid to water, never water to acid.
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