Molarity Calculator

Welcome to the Molarity Calculator, a comprehensive chemistry tool for calculating solution concentrations. Whether you need to find the molarity of a solution, determine how much solute to weigh, calculate the required volume, or perform dilution calculations, this calculator provides step-by-step solutions with clear formula explanations.

What is Molarity?

Molarity (M), also known as molar concentration, is the most common unit for expressing the concentration of a solution in chemistry. It represents the number of moles of solute dissolved per liter of solution. Molarity is essential for stoichiometric calculations, preparing laboratory solutions, and quantitative chemical analysis.

Molarity Formula

Since moles = mass ÷ molar mass, we can express molarity as:

Where:

• M = Molarity (mol/L or M)
• n = Number of moles of solute (mol)
• m = Mass of solute (g)
• MW = Molar mass of solute (g/mol)
• V = Volume of solution (L)

How to Use This Calculator

1. Select calculation type: Choose what you want to calculate - molarity, mass, volume, or use the dilution calculator.
2. Select a compound (optional): Click on a common compound to auto-fill its molar mass, or enter a custom molar mass.
3. Enter known values: Fill in the values you know, selecting appropriate units (g/mg/kg for mass, L/mL for volume).
4. Calculate: Click the calculate button to see results with step-by-step formula breakdown.

Calculation Types Explained

1. Calculate Molarity

Use this when you know the mass of solute, its molar mass, and the volume of solution. The calculator will determine the concentration in mol/L.

2. Calculate Mass of Solute

Use this when preparing a solution of specific molarity. Enter your target molarity, molar mass, and desired volume to find how much solute to weigh.

3. Calculate Volume

Use this when you have a fixed amount of solute and want to achieve a specific molarity. The calculator tells you what volume of solution to prepare.

4. Dilution Calculator

Use the dilution equation M₁V₁ = M₂V₂ to calculate how to dilute a stock solution. Enter any three values to find the fourth.

Common Compounds Reference

Step-by-Step Example

Problem: Calculate the molarity when 11.7 g of NaCl is dissolved in 500 mL of solution.

1. Convert units: 500 mL = 0.5 L
2. Calculate moles: n = 11.7 g ÷ 58.44 g/mol = 0.2 mol
3. Calculate molarity: M = 0.2 mol ÷ 0.5 L = 0.4 M

Preparing Solutions: Best Practices

• Always dissolve the solute in less solvent than the final volume, then add solvent to reach the target volume
• Use a volumetric flask for accurate final volume measurements
• For acids, always add acid to water (not water to acid) for safety
• Allow solutions to reach room temperature before making final volume adjustments
• Label all prepared solutions with compound name, concentration, date, and preparer

Molarity vs Other Concentration Units

Frequently Asked Questions

What is molarity?

Molarity (M) is a measure of concentration that expresses the number of moles of solute per liter of solution. It is one of the most commonly used units in chemistry for describing solution concentrations. The formula is M = n/V, where n is the number of moles of solute and V is the volume of solution in liters.

How do I calculate molarity from mass?

To calculate molarity from mass: 1) Convert mass to grams if needed, 2) Calculate moles by dividing mass by molar mass (n = mass/molar mass), 3) Convert volume to liters if needed, 4) Calculate molarity by dividing moles by volume (M = n/V). For example, 5.844g NaCl (molar mass 58.44 g/mol) in 1L gives 0.1M solution.

What is the dilution formula?

The dilution formula is M₁V₁ = M₂V₂, where M₁ is the initial molarity, V₁ is the initial volume, M₂ is the final molarity, and V₂ is the final volume. This equation works because the total amount of solute remains constant during dilution.

How do I prepare a solution of specific molarity?

To prepare a solution: 1) Calculate the required mass using mass = M × molar mass × V, 2) Weigh out the calculated mass of solute, 3) Dissolve in a small amount of solvent, 4) Transfer to a volumetric flask and add solvent to the final desired volume.

What is the difference between molarity and molality?

Molarity (M) is moles of solute per liter of solution, while molality (m) is moles of solute per kilogram of solvent. Molarity depends on temperature (since volume changes with temperature), while molality does not. Molarity is more commonly used in laboratory settings.

Additional Resources

• Molar Concentration - Wikipedia
• Dilution Equation - Wikipedia