Molarity Calculator: Calculate Solution Concentration
Our free molarity calculator helps you quickly calculate molarity, moles, mass, volume, and perform dilution calculations for chemical solutions. Perfect for chemistry students, lab technicians, and researchers.
What is Molarity?
Molarity (M) is a measure of concentration that expresses the number of moles of solute per liter of solution. It's one of the most common units used in chemistry to describe solution concentration. The formula for molarity is:
M = n / V
Where M is molarity (mol/L), n is the number of moles of solute, and V is the volume of solution in liters.
Calculator Features
- Calculate Molarity: Find concentration when you know moles and volume
- Calculate Moles: Determine amount of substance from molarity and volume
- Calculate Mass: Find mass needed from moles and molar mass
- Calculate Volume: Determine solution volume from moles and molarity
- Dilution Calculator: Use M₁V₁ = M₂V₂ formula for dilutions
- Instant Results: Real-time calculations as you type
- Step-by-Step: Shows calculation steps and formulas
How to Use the Molarity Calculator
Calculating Molarity
To calculate molarity:
- Select "Calculate Molarity (M)" from the dropdown
- Enter the number of moles (n) of solute
- Enter the volume (V) of solution in liters
- Click "Calculate" to get the molarity
Example: If you have 0.5 moles of NaCl in 1 liter of solution, the molarity is 0.5 M.
Calculating Moles
To find the number of moles:
- Select "Calculate Moles (n)"
- Enter the molarity (M) of the solution
- Enter the volume (V) in liters
- The calculator shows moles = M × V
Calculating Mass
To calculate mass of solute needed:
- Select "Calculate Mass (g)"
- Enter the number of moles needed
- Enter the molar mass (molecular weight) in g/mol
- Get the mass in grams
Dilution Calculations
For diluting solutions:
- Select "Dilution Calculator"
- Enter initial molarity (M₁)
- Enter initial volume (V₁)
- Enter desired final molarity (M₂)
- Get the final volume and amount of solvent to add
Important Formulas
Molarity Formula
M = n / V
Where:
- M = Molarity (mol/L or M)
- n = Number of moles (mol)
- V = Volume of solution (L)
Moles Formula
n = M × V
Calculate moles from molarity and volume.
Mass Formula
mass = n × MW
Where:
- mass = Mass in grams (g)
- n = Number of moles (mol)
- MW = Molar mass (g/mol)
Volume Formula
V = n / M
Calculate volume from moles and molarity.
Dilution Formula
M₁V₁ = M₂V₂
Where:
- M₁ = Initial molarity
- V₁ = Initial volume
- M₂ = Final molarity
- V₂ = Final volume
Common Applications
- Chemistry Labs: Prepare solutions with precise concentrations
- Titrations: Calculate concentrations in acid-base titrations
- Stock Solutions: Dilute concentrated stock solutions to working concentrations
- Buffer Preparation: Make buffer solutions with specific pH
- Research: Prepare reagents for experiments
- Quality Control: Verify solution concentrations
- Education: Learn and practice molarity calculations
- Pharmaceutical: Prepare drug solutions with exact concentrations
Step-by-Step Examples
Example 1: Calculating Molarity
Problem: You dissolve 0.5 moles of NaCl in enough water to make 2 liters of solution. What is the molarity?
Solution:
- Given: n = 0.5 mol, V = 2 L
- Formula: M = n / V
- M = 0.5 mol / 2 L = 0.25 M
- Answer: The molarity is 0.25 M
Example 2: Calculating Moles
Problem: How many moles are in 500 mL of a 2 M solution?
Solution:
- Given: M = 2 M, V = 500 mL = 0.5 L
- Formula: n = M × V
- n = 2 M × 0.5 L = 1 mol
- Answer: There is 1 mole of solute
Example 3: Calculating Mass
Problem: What mass of NaCl (MW = 58.44 g/mol) is needed to make 1 L of 0.5 M solution?
Solution:
- First find moles: n = M × V = 0.5 M × 1 L = 0.5 mol
- Then find mass: mass = n × MW
- mass = 0.5 mol × 58.44 g/mol = 29.22 g
- Answer: You need 29.22 grams of NaCl
Example 4: Dilution Calculation
Problem: You have 10 mL of 10 M HCl. How much water should you add to make a 1 M solution?
Solution:
- Given: M₁ = 10 M, V₁ = 10 mL, M₂ = 1 M
- Formula: M₁V₁ = M₂V₂
- 10 M × 10 mL = 1 M × V₂
- V₂ = 100 mL
- Water to add = V₂ - V₁ = 100 mL - 10 mL = 90 mL
- Answer: Add 90 mL of water
Unit Conversions
Common unit conversions for molarity calculations:
- Volume: 1 L = 1000 mL = 1000 cm³
- Molarity: 1 M = 1 mol/L = 1000 mmol/L
- Millimolar: 1 mM = 0.001 M
- Micromolar: 1 μM = 0.000001 M
Tips for Accurate Calculations
- Check Units: Always ensure volume is in liters for molarity calculations
- Molar Mass: Use accurate molar mass values from periodic table
- Significant Figures: Maintain appropriate significant figures
- Temperature: Note that molarity changes with temperature (volume changes)
- Dilution Safety: Always add acid to water, never water to acid
- Verify Results: Double-check calculations for critical applications
- Stock Solutions: Label all solutions with concentration and date
Common Mistakes to Avoid
- Wrong Volume Units: Forgetting to convert mL to L
- Confusing Formulas: Using wrong formula for the calculation type
- Molar Mass Errors: Using incorrect molecular weight
- Dilution Errors: Confusing final volume with volume to add
- Rounding Too Early: Rounding intermediate values causes errors
- Unit Mismatch: Mixing different concentration units
Frequently Asked Questions
What's the difference between molarity and molality?
Molarity (M) is moles per liter of solution, while molality (m) is moles per kilogram of solvent. Molarity depends on temperature (volume changes), but molality doesn't.
How do I convert between molarity and percent concentration?
You need to know the density and molar mass. Percent concentration is (mass of solute / mass of solution) × 100. Use the density to convert between mass and volume.
Can I use this calculator for any solute?
Yes! The calculator works for any solute. Just make sure you use the correct molar mass for your specific compound.
Why is molarity temperature-dependent?
Because molarity is based on volume, and volume changes with temperature. As temperature increases, liquids expand, decreasing molarity. For precise work, specify the temperature.
How accurate should my measurements be?
For most lab work, 3-4 significant figures is sufficient. For critical applications like pharmaceutical preparations, higher precision may be required.
Safety Considerations
- Dilution Safety: Always add concentrated acid to water, never the reverse
- Heat Generation: Some dilutions generate heat - use caution
- PPE: Wear appropriate personal protective equipment
- Ventilation: Work in well-ventilated areas or fume hoods
- Labeling: Properly label all solutions with concentration and hazards
- Storage: Store solutions according to safety guidelines