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MonoCalc

Molarity Calculator

Chemistry

M = n / V (or M = mass / (molar_mass × V_L))

Find Molarity (M)

Load example:

Leave blank if entering moles directly
From periodic table or compound formula
Direct entry; overrides mass + molar mass if provided
Total volume of the final solution

About This Tool

⚗️ Molarity Calculator – Find M, Moles, Mass, or Volume

The Molarity Calculator is a free online chemistry tool that helps you calculate solution concentration in mol/L (molarity), find unknown moles, derive the required mass of solute, or determine the volume needed to reach a target concentration. It also includes a built-in dilution calculator using the M₁V₁ = M₂V₂ relationship.

Whether you are a student preparing for a chemistry exam, a lab technician making standard solutions, or a researcher calculating reagent quantities — this tool provides instant, step-by-step results with automatic unit conversion between mL/L and g/mg.

📘 What is Molarity?

Molarity (M) is the most commonly used measure of solution concentration in chemistry. It expresses the number of moles of solute dissolved in exactly one liter of solution:

M = n / V

where M is molarity (mol/L), n is moles of solute, and V is the total volume of solution in liters. It is distinct from molality, which uses kilograms of solvent rather than liters of solution.

⚙️ Calculation Modes Explained

The tool supports five calculation modes:

1. Find Molarity

If you know the mass of solute and the molar mass (from the periodic table or compound formula), the calculator first converts mass to moles using:

n = mass (g) / molar mass (g/mol)

Then it computes molarity:

M = n / V(L)

You can also enter moles directly if already known, bypassing the mass/molar-mass step.

2. Find Moles

Given molarity and volume, the number of moles is simply:

n = M × V(L)

3. Find Mass

To calculate the mass of solute needed to make a solution of known molarity and volume:

mass = M × molar_mass × V(L)

4. Find Volume

To find the volume of solution required when you know moles and target molarity:

V = n / M

5. Dilution Calculator (M₁V₁ = M₂V₂)

When you dilute a solution you add solvent — the moles of solute remain constant. This leads to the dilution formula:

M₁ × V₁ = M₂ × V₂

Provide any three of the four variables (M₁, V₁, M₂, V₂) and the calculator solves for the missing one. The result panel indicates whether the process is a dilution (V₂ > V₁) or a concentration (V₂ < V₁).

🧮 Practical Examples

NaCl Standard Solution

Problem: Dissolve 10 g of NaCl (molar mass = 58.44 g/mol) in 500 mL of solution. What is the molarity?
Step 1: n = 10 / 58.44 = 0.1711 mol
Step 2: V = 500 mL = 0.5 L
Step 3: M = 0.1711 / 0.5 = 0.3422 mol/L

Dilution Example – H₂SO₄

Problem: Dilute a 1.0 M H₂SO₄ solution by taking 50 mL and adding water to make 200 mL total. What is the final molarity?
Formula: M₂ = (M₁ × V₁) / V₂ = (1.0 × 0.05) / 0.2 = 0.25 M

Glucose Solution

Problem: Prepare a 0.05 M glucose (molar mass = 180.16 g/mol) solution in 1 L. How much glucose is needed?
Step 1: n = 0.05 × 1 = 0.05 mol
Step 2: mass = 0.05 × 180.16 = 9.008 g

💡 Tips for Accurate Results

  • Use molar mass from the periodic table for accuracy. Common values: NaCl = 58.44, NaOH = 40.00, HCl = 36.46, H₂SO₄ = 98.08, Glucose = 180.16 g/mol.
  • Volume means total solution volume, not the volume of solvent added. After dissolving the solute, add solvent until the final volume is reached.
  • For dilution problems, always measure V₁ (aliquot) before adding the solvent, then bring to V₂ in a volumetric flask.
  • Temperature matters in real laboratory work. Molarity is defined at a specific temperature since liquid volume changes with temperature.

🔄 Unit Conversions Used

The calculator handles the following conversions automatically:

  • 1 L = 1000 mL — mL inputs are converted to L before molarity calculations
  • 1 g = 1000 mg — mg inputs are converted to g for mole calculations

All intermediate conversions are shown in the step-by-step panel so you can verify each transformation.

🔗 Related Chemistry Concepts

Molarity is closely related to other concentration measures in chemistry. Molality (mol/kg) uses mass of solvent instead of volume. Normality (N) accounts for equivalents in acid-base or redox reactions. For gas-phase calculations, the Ideal Gas Law (PV = nRT) provides an alternative route to find moles from pressure, volume, and temperature. The density calculator can help convert between mass and volume when working with non-aqueous solutions.

Frequently Asked Questions

Is the Molarity Calculator free?

Yes, Molarity Calculator is totally free :)

Can I use the Molarity Calculator offline?

Yes, you can install the webapp as PWA.

Is it safe to use Molarity Calculator?

Yes, any data related to Molarity Calculator only stored in your browser (if storage required). You can simply clear browser cache to clear all the stored data. We do not store any data on server.

What is molarity and how is it calculated?

Molarity (M) measures the concentration of a solution as the number of moles of solute per liter of solution. The formula is M = n / V, where n is moles of solute and V is volume in liters. If you have mass instead of moles, first compute n = mass (g) / molar mass (g/mol).

How do I use this calculator to find molarity from mass?

Select 'Find Molarity', enter the mass of your solute and its molar mass (found from the periodic table or compound formula), then enter the volume of solution. The calculator converts units automatically and shows a step-by-step derivation.

What is the dilution formula M₁V₁ = M₂V₂?

When you dilute a solution, the number of moles of solute stays constant. This gives M₁V₁ = M₂V₂, where M₁ and V₁ are the initial molarity and volume, and M₂ and V₂ are the final molarity and volume after dilution. You can solve for any one unknown if the other three are known.

What units should I use for volume?

You can enter volume in milliliters (mL) or liters (L). The calculator automatically converts mL to L before computing, since the molarity formula requires volume in liters. The step-by-step panel shows the conversion explicitly.

How accurate are the results?

Results are computed to 6 significant figures internally and displayed to 4 significant figures. Accuracy depends on the precision of your inputs — use the most accurate molar mass available. Real-world results may vary due to measurement errors in lab equipment.

Can I calculate the volume needed to prepare a solution of a given molarity?

Yes, select 'Find Volume'. Enter the target molarity, the moles or mass + molar mass of your solute, and the calculator will output the required volume to achieve that concentration. You can choose to display the result in mL or L.