Molarity Vs Molality: Formula And Definitions - Technology Networks

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Molarity measures solute per volume, molality per mass. Learn the key differences and how to calculate each.

Article Last Updated: December 18, 2023 Written by Nicole Gleichmann Nicole Gleichmann Freelance Writer Nicole is a freelance writer specializing in biology, health and technology. She received her undergraduate degree in Organismal Biology from Scripps College in California. Here, her passion for holistic health and wellness began, leading to a previous position as a nutrition and wellness coach and expanding to freelance health writing. Learn about our editorial policies Credit: iStock Download Article Listen with Speechify 0:00 Register or log In for free to listen to this article Read time: 4 minutes

Both molarity and molality are measures of a chemical solution’s concentration. The primary difference between the two comes down to mass versus volume.

Contents

Molality definition

- Molality formula and units

- Molality equation

Molarity definition

- Molarity formula and units

- Molarity equation

Molarity vs molality

Molarity calculator

Molality calculator

The molality describes the moles of a solute in relation to the mass of a solvent, while the molarity is concerned with the moles of a solute in relation to the volume of a solution.

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Read on to learn more about molarity and molality, including their definitions, equations, and a comparison of the two terms.

Molality definition

Molality (m), or molal concentration, is the amount of a substance dissolved in a certain mass of solvent. It is defined as the moles of a solute per kilograms of a solvent. [Updated May 4, 2020].

Molality formula and units

The units of molality are m or mol/kg.

Molality equation

m = moles solute / kilograms solvent

Molarity definition

Molarity (M) is the amount of a substance in a certain volume of solution. Molarity is defined as the moles of a solute per liters of a solution. Molarity is also known as the molar concentration of a solution.

Molarity formula and units

The units of molarity are M or mol/L. A 1 M solution is said to be “one molar.”

Molarity equation

M = moles solute / liters solution

Molarity vs molality

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An important distinction between molality and molarity is the difference between a solution and a solvent.

Molarity is the ratio of the moles of a solute to the total liters of a solution. The solution includes both the solute and the solvent.

Molality, on the other hand, is the ratio of the moles of a solute to the kilograms of a solvent. Note that the mass used in the denominator is that of only the solvent, not the solute and the solvent.

Molarity (M)	Molality (m)
Measure of	Concentration	Concentration
Definition	The moles of a solute per liters of a solution	The moles of a solute per kilograms of a solvent
Units	M	m
Equation	M = moles solute / liters solution	m = moles solute / kg solvent
Ratio of moles to:	Volume (in liters)	Mass (in kilograms)

Molarity calculator

Find a handy calculator for determining the molarity of a solution here.

Molality calculator

A calculator for molality can be found here.

This article was updated May 4, 2020 to clarify the definition of molality.

Meet the Author Nicole Gleichmann Freelance Writer Nicole is a freelance writer specializing in biology, health and technology. Before beginning her career as a writer, Nicole received her undergraduate degree in Organismal Biology from Scripps College in California. It was here that her passion for holistic health and wellness began, which led to a previous position as a nutrition and wellness coach and expanded to freelance health writing. You can find her articles on Technology Networks, Everyday Health, Health, CannaMD, and CBD Hacker. Advertisement Advertisement Advertisement Never miss a story with the Breaking Science News daily newsletter Subscribe for FREE