How do you calculate molarity?

Molarity (M) is calculated by dividing the number of moles of solute by the volume of solution in liters: M = n ÷ V. To find moles, divide the mass of solute (in grams) by its molecular weight (g/mol). For example, 58.44 g of NaCl (MW = 58.44 g/mol) dissolved in 1 liter gives exactly 1 M NaCl.

How do you calculate molarity from concentration in g/L?

To convert g/L to molarity, divide the concentration in grams per liter by the molecular weight of the solute: M = (g/L) ÷ MW. For example, if you have 36.46 g/L of HCl (MW = 36.46 g/mol), the molarity is 36.46 ÷ 36.46 = 1.0 M.

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 changes with temperature because liquid volume changes with temperature; molality does not. Molality is preferred for colligative property calculations (freezing point depression, boiling point elevation).

How do you dilute a solution using M₁V₁ = M₂V₂?

The dilution equation M₁V₁ = M₂V₂ relates the concentration and volume before and after dilution. To find the volume of stock solution needed: V₁ = (M₂ × V₂) ÷ M₁. For example, to make 500 mL of 0.1 M from a 1 M stock: V₁ = (0.1 × 0.5) ÷ 1 = 0.05 L = 50 mL of stock, then add solvent to 500 mL total.

How do you calculate moles from molarity and volume?

Multiply molarity by volume in liters: moles = M × V. For example, 2 M HCl in 0.5 L contains 2 × 0.5 = 1 mole of HCl. Make sure volume is in liters (not mL). To convert mL to L, divide by 1000.

How do you calculate the mass needed to make a molar solution?

Use the formula: mass (g) = Molarity × Molecular Weight × Volume (L). To make 500 mL of 1 M NaCl: mass = 1 × 58.44 × 0.5 = 29.22 g. Dissolve 29.22 g NaCl in water, then add water to a final volume of 500 mL.

What is the molarity of pure water?

The molarity of pure water is approximately 55.5 M. This is calculated from water's density (1000 g/L) divided by its molecular weight (18.015 g/mol): 1000 ÷ 18.015 ≈ 55.5 mol/L. This value is used in equilibrium calculations involving water.

How do you calculate pH from molarity?

For strong acids, pH = -log₁₀[H⁺]. A 0.01 M HCl solution has pH = -log(0.01) = 2. For strong bases, pOH = -log[OH⁻] and pH = 14 - pOH. For weak acids/bases, you need the Ka or Kb value to find the equilibrium concentration of H⁺ or OH⁻ ions first.

Molarity Calculator

Solve For

Find concentration (mol/L)

Common Compound

Mass of Solute

Molecular Weight

g/mol

Volume of Solution

Calculated Molarity

1.0000M (mol/L)

Solution Breakdown

All values in base units

Molarity

1.0000mol/L

Mass

58.4400g

Volume

1.0000L

Molecular Weight

58.44g/mol

Moles of Solute

1.0000mol

Formula Used

Step-by-step calculation with your values

M = mass ÷ (MW × V) = 58.4400 g ÷ (58.44 g/mol × 1.00000 L) = 1.00000 mol/L

How the Molarity Calculator Works

Core formulas for molar concentration calculations

Molarity (M) measures the concentration of a solution as the number of moles of solute per liter of solution. This calculator uses the fundamental relationship between mass, molecular weight, volume, and concentration to solve for any unknown variable.

Molarity

M = mass ÷ (MW × V)

Result in mol/L

Mass

mass = M × MW × V

Result in grams

Volume

V = mass ÷ (MW × M)

Result in liters

Molecular Weight

MW = mass ÷ (M × V)

Result in g/mol

Example — 58.44 g NaCl in 1 L of solution

Mass

58.44

NaCl powder

58.44

NaCl mol. wt.

g/mol

Moles

1.000

58.44 ÷ 58.44

mol

Molarity

1.000

1.0 ÷ 1.0

What Is Molarity?

Understanding molar concentration in chemistry

Molarity (symbol: M) is the most common way to express the concentration of a solution in chemistry. It is defined as the number of moles of solute dissolved in one liter of solution. A 1 M solution of NaCl means there is 1 mole (58.44 g) of sodium chloride per liter of solution.

Key Definitions

Molarity (M) = moles of solute ÷ liters of solution

Mole (mol) = 6.022 × 10²³ particles (Avogadro's number)

Molecular Weight = mass of 1 mole of a substance (g/mol)

Molarity depends on the total volume of solution, not the volume of solvent alone. When making a molar solution, dissolve the solute first, then add solvent to reach the target volume.

Molarity vs. Molality

Two commonly confused concentration measures

Property	Molarity (M)	Molality (m)
Definition	mol per L of solution	mol per kg of solvent
Temperature dependent?	Yes (volume changes with T)	No (mass is constant)
Units	M or mol/L	m or mol/kg
When to use	Most lab work at standard T	Colligative property calcs

Common Mistakes to Avoid

Frequent errors in molarity calculations

Using solvent volume instead of solution volume

Molarity uses the total volume of solution. If you dissolve 58 g NaCl in 1 L of water, the total solution volume is slightly more than 1 L. For precise work, dissolve the solute first, then add solvent to the desired volume mark.

Forgetting to convert units

Mass must be in grams and volume in liters before applying M = mass/(MW × V). Using mg or mL without conversion leads to results off by factors of 1,000.

Confusing moles and molarity

Moles is an absolute quantity (like “2 moles of NaCl”). Molarity is a concentration — moles per liter. Doubling the volume halves the molarity but keeps moles constant.

Mixing up molecular weight and molar mass

For practical purposes, molecular weight (in daltons) and molar mass (in g/mol) have the same numerical value. Both can be used interchangeably in molarity calculations.

Common Laboratory Solutions

Reference concentrations for frequently used solutions

Solution	Common Conc.	MW (g/mol)	g/L for 1 M
NaCl (saline)	0.154 M (0.9%)	58.44	58.44
HCl (conc.)	12.1 M (37%)	36.46	36.46
NaOH	1 M or 10 M	40.00	40.00
H₂SO₄ (conc.)	18.0 M (96%)	98.08	98.08
Glucose	0.278 M (5%)	180.16	180.16
PBS (1×)	~0.01 M phosphate	—	—
Tris buffer	0.05–1 M	121.14	121.14
EDTA	0.5 M	372.24	372.24

Frequently Asked Questions

Common questions and detailed answers

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Last updated Mar 26, 2026

Molarity Calculator

Solution Breakdown

Formula Used

How the Molarity Calculator Works

What Is Molarity?

Molarity vs. Molality

Common Mistakes to Avoid

Common Laboratory Solutions

Frequently Asked Questions

Embed Molarity Calculator

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