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Molarity Calculator

Calculate the molar concentration of a solution from solute mass, molar mass and solution volume.

NaCl = 58.44 g/mol

Molarity
1 mol/L
Amount of solute
0.1 mol
Millimolar
1000 mM

Step-by-step working

  1. n = mass / M = 5.844 g / 58.44 g/mol = 0.1 mol
  2. V = 100 mL = 0.1 L
  3. c = n / V = 1 mol/L

Mathematical Formula

n = m / M; c = n / V (V in litres). Result in mol/L (M).

Overview & Explanation

Molarity (amount concentration) is moles of solute per litre of solution.

How It Works

  • Convert mass to moles.
  • Convert mL to L.
  • Divide moles by volume.

Practical Applications

  • Preparing lab reagents.
  • Chemistry homework.

How molarity is calculated

Molarity (M) is moles of solute per litre of solution: M = n / V. To get the moles n, divide the mass of solute in grams by its molar mass in g/mol. V is the final volume of the whole solution in litres, not the volume of water you started with.

Example: 5.85 g of sodium chloride (molar mass 58.44 g/mol) is 5.85 / 58.44 = 0.1001 mol. Dissolved and made up to 500 mL (0.5 L), that gives 0.1001 / 0.5 = 0.200 M.

Dilution with M1V1 = M2V2

Adding solvent changes the volume but not the moles of solute, so M1 x V1 = M2 x V2. To make 250 mL of 0.2 M solution from a 1 M stock, V1 = 0.2 x 250 / 1 = 50 mL. Measure 50 mL of stock and add water up to the 250 mL mark.

Example 1: 5.844 g NaCl in 100 mL

1.0 M.

1

Inputs

Mass of solute (g): 5.844 · Molar mass (g/mol): 58.44 · Solution volume (mL): 100

= entered
2

Step 1

n = mass / M = 5.844 g / 58.44 g/mol = 0.1 mol

3

Step 2

V = 100 mL = 0.1 L

4

Step 3

c = n / V = 1 mol/L

5

Molarity

Result

= 1 mol/L

Example 2: 4 g NaOH in 250 mL

M = 40.00 g/mol.

1

Inputs

Mass of solute (g): 4 · Molar mass (g/mol): 40 · Solution volume (mL): 250

= entered
2

Step 1

n = mass / M = 4 g / 40 g/mol = 0.1 mol

3

Step 2

V = 250 mL = 0.25 L

4

Step 3

c = n / V = 0.4 mol/L

5

Molarity

Result

= 0.4 mol/L

How it's calculated & sources

n = m / M; c = n / V (V in litres). Result in mol/L (M).

Frequently Asked Questions

Molarity vs molality?
Molarity is per litre of solution; molality is per kilogram of solvent.
Where do I get molar mass?
Sum atomic masses from the periodic table, or use the molar mass calculator.
Does temperature matter?
Yes, slightly: volume changes with temperature, so molarity does too.
Is molarity the same as molality?
No. Molality is moles per kilogram of solvent. Molarity uses litres of solution, so it changes slightly with temperature as the liquid expands.
Why make up to volume instead of adding a fixed amount of water?
The solute takes up some volume itself, so adding exactly 500 mL of water would give slightly more than 500 mL of solution and a lower concentration.

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