# Molarity vs. Molality: What's the Difference?

Edited by Janet White || By Harlon Moss || Published on January 1, 2024
Molarity is the concentration of a solution expressed as moles of solute per liter of solution, while molality is the concentration expressed as moles of solute per kilogram of solvent.

## Key Differences

Molarity (M) is defined as moles of solute per liter of solution, making it volume-dependent. Molality (m), in contrast, is defined as moles of solute per kilogram of solvent, making it mass-dependent.
Molarity changes with temperature, as it is based on volume which can expand or contract with temperature. Molality, however, remains unaffected by temperature changes since it's based on mass.
Molarity is commonly used in chemistry, especially in reactions occurring in solutions. Molality is often used in scenarios involving boiling point elevation and freezing point depression.
To calculate molarity, one must know the total volume of the solution. For molality, the mass of the solvent is required, independent of the total volume of the solution.
Molarity is used in standard laboratory procedures and calculations, while molality is more useful in physical chemistry, particularly in studying colligative properties.

## Comparison Chart

### Units of Measurement

Moles of solute per liter of solution
Moles of solute per kilogram of solvent

### Temperature Dependency

Changes with temperature
Unaffected by temperature

### Common Usage

Reactions in solutions, standard lab work
Colligative properties, physical chemistry

### Dependence on

Volume of solution
Mass of solvent

### Calculation Basis

Total solution volume
Solvent mass regardless of solution volume

## Molarity and Molality Definitions

#### Molarity

Measure of solute concentration per liter of solution.
A 1 M NaCl solution has one mole of sodium chloride per liter.

#### Molality

Used in studying boiling point elevation.
The molality of the solution determines its boiling point.

#### Molarity

Concentration expressed based on solution volume.
To prepare a 0.5 M solution, dissolve the solute in enough water to make 1 liter.

#### Molality

Important in physical chemistry calculations.
Calculating molality is crucial for osmotic pressure studies.

#### Molarity

Indicator of how reactive a solution can be.
Higher molarity usually means more reactive solutions.

#### Molality

Concentration measure not affected by volume.
Molality is preferred in experiments where temperature fluctuates.

#### Molarity

A common term used in chemical calculations.
The molarity of the acid was key to the experiment's success.

#### Molality

Measure of solute concentration per kilogram of solvent.
A molality of 2 m means 2 moles of solute per kilogram of water.

#### Molarity

Essential for preparing solutions in labs.
Accurate molarity is crucial for precise experimental results.

#### Molality

Remains constant with temperature changes.
Molality is useful in high-temperature conditions.

#### Molarity

Abbr. M The concentration of a solution expressed in moles of solute per liter of solution.

#### Molality

Abbr. m The concentration of a solution expressed in moles of solute per kilogram of solvent. Also called molal.

#### Molarity

(chemistry) the concentration of a substance in solution, expressed as the number of moles of solute per litre of solution

#### Molality

(chemistry) the concentration of a substance in solution, expressed as the number of moles of solute per kilogram of solvent

#### Molarity

Concentration measured by the number of moles of solute per liter of solvent

#### Molality

A measure of concentaration of substances in mixtures, 1 molal being the concentration of a solution containing 1 mole of solute per 1000 grams of solvent. Compare molar.

#### Molality

Molal concentration

## FAQs

#### Why does temperature affect molarity?

Temperature affects the volume of the solution, and since molarity is volume-dependent, it changes with temperature.

#### Is molality affected by temperature?

No, molality is based on mass and is not affected by temperature changes.

#### When is molarity used in chemistry?

Molarity is used in calculating reactions in solutions and standard laboratory procedures.

#### What is the significance of molality in physical chemistry?

Molality is important in studying colligative properties like boiling point elevation.

#### How is molality different from molarity?

Molality measures moles of solute per kilogram of solvent, unlike molarity which is per liter of solution.

#### Does molality change with dilution?

No, because molality is independent of the solution’s total volume.

#### What are the units of molarity?

Molarity is expressed in moles per liter (M).

#### What is molarity?

Molarity is the concentration of a solute in a solution, measured in moles per liter.

#### How do you calculate molarity?

Calculate molarity by dividing the moles of solute by the liters of solution.

#### What's the formula for molality?

Molality is calculated by dividing the moles of solute by the kilograms of solvent.

#### Why is molarity important in titrations?

Molarity is key to determining the concentration of reactants in titration.

#### Can molarity be converted to molality?

Yes, but it requires additional information like solvent density.

#### Can molarity change during a reaction?

Yes, if the solution’s volume changes during the reaction, molarity can change.

#### Can molality be used in environmental studies?

Yes, especially in studies involving temperature-sensitive processes.

#### What affects the accuracy of molarity?

Accurate measurement of solution volume and solute amount affects molarity accuracy.

#### What units are used for molality?

Molality is expressed in moles per kilogram (m).

#### Is molarity used in industry?

Yes, it's used in pharmaceuticals and other industries for solution preparation.

#### Is molality more reliable in certain conditions?

Yes, in conditions with large temperature fluctuations, molality is more reliable.

#### Why choose molality over molarity in some cases?

Molality is chosen for its temperature independence and relevance in studying certain properties of solutions.

#### How does molality relate to freezing point depression?

The molality of a solution helps determine the extent of freezing point depression.