Molarity Calculator
Step-by-Step Solution
What is Molarity?
Molarity (M) is a measure of the concentration of a solution. It is defined as the number of moles of solute per liter of solution.
M = n / V
where n = moles of solute, V = volume in liters
Our free online molarity calculator helps you quickly convert between mass, moles, volume, and concentration with clear step-by-step explanations.
How to Calculate Molarity
The molarity formula is straightforward once you understand the components. First convert your inputs into consistent units, then apply the relationship between moles and volume.
Core Formulas
- Molarity (M): M = moles of solute / liters of solution
- Moles: n = mass (g) / molar mass (g/mol)
- Mass needed: mass = M × V × molar mass
Worked Examples
Example 1: Basic Calculation
Problem: What is the molarity of a solution made by dissolving 58.44 g of NaCl in 1 liter of water? (Molar mass of NaCl = 58.44 g/mol)
Solution:
Moles of NaCl = 58.44 / 58.44 = 1 mol
M = 1 mol / 1 L = 1 M
Example 2: Volume in mL
Problem: Calculate the molarity when 5.85 g of NaCl is dissolved in 250 mL of solution.
Step 1: Moles = 5.85 / 58.44 ≈ 0.1 mol
Step 2: Volume = 0.250 L
Molarity: 0.1 / 0.250 = 0.4 M
Example 3: Find Required Mass
Problem: How many grams of glucose (C₆H₁₂O₆, 180 g/mol) are needed to make 500 mL of 0.2 M solution?
Moles needed = 0.2 × 0.5 = 0.1 mol
Mass = 0.1 × 180 = 18 g
Example 4: Dilution Context
Problem: You have 2.5 M stock solution. How much stock is needed to prepare 100 mL of 0.5 M solution?
Using M₁V₁ = M₂V₂ → V₁ = (0.5 × 100) / 2.5 = 20 mL
Concentration Units Comparison
| Unit | Definition | When to Use |
|---|---|---|
| Molarity (M) | moles / liter solution | Most common for reactions |
| Molality (m) | moles / kg solvent | Colligative properties |
| Normality (N) | equivalents / liter | Acid-base titrations |
| Weight % | (mass solute / mass solution) × 100 | Industrial preparations |
Real-Life Applications
- Preparing laboratory reagents and standard solutions
- Pharmaceutical drug formulation and dosing calculations
- Industrial chemical manufacturing and quality control
- Environmental testing of water and soil samples
- Biochemical experiments and cell culture media preparation
- Food and beverage industry concentration control
Key Properties & Rules
- Molarity depends on temperature because volume changes with temperature
- 1 M solution contains 1 mole of solute in 1 liter of total solution (not solvent)
- Always add solute to solvent, then top up to final volume for accuracy
- For dilute aqueous solutions, 1 mL ≈ 1 g (density of water)