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Chemistry

Molality

Measure solute amount per kilogram of solvent.

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Source & review

Difficulty

Beginner

Read time

3 min

Prerequisites

Basic algebra and molar quantities

Review statusNeeds review

Source

OpenStax, Chemistry 2e, §11.4

Adapted from Teng-Jui Lin’s CHEM 145 equation sheet. The linked textbook reference was used to check the equation and its physical context. Pending editorial review.

Adapted from Teng-Jui Lin, Equation Sheets, under CC BY 4.0.

FormuLab adapted notation and chemical symbols, added variable meanings, units, applicability conditions, and an original worked example.

Definition
Understanding the core concept

Molality uses the mass of the solvent, rather than the volume or mass of the whole solution. This makes it useful in colligative-property calculations where temperature changes the solution’s volume.

Variables & Units
Understanding each component
SymbolMeaningUnits
Molality
Amount of solute
Mass of solvent, excluding solute
Real-World Applications
Where this formula is used in practice

Solution preparation

Describe a solution using solvent mass.

Colligative properties

Provide the concentration for freezing and boiling point shifts.

Worked Example
Step-by-step calculation with real numbers

Problem

A solution contains 0.500 mol of solute dissolved in 2.00 kg of solvent. Find its molality.

Given

Solution

1
2
3

Final Answer

FormuLab is a study reference. Verify formulas, units, assumptions, and course-specific conventions before relying on them.

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