Amount concentration, molality and composition fractions
Concentration must declare its numerator and denominator.
Key knowledge
Amount concentration (molarity) is solute amount per solution volume; molality is solute amount per solvent mass. Mole fraction and mass fraction divide a component's amount or mass by the corresponding total. These scales are not interchangeable. Volume-based concentration can change with temperature through expansion even when composition and solute amount are unchanged.
Values and equations
c_i = n_i/V_solution; b_i = n_i/m_solvent; x_i = n_i/sum_j(n_j); w_i = m_i/sum_j(m_j)
- c_i
- amount concentration of component i mol m^-3
- b_i
- molality of solute i mol kg^-1
- x_i
- mole fraction of component i 1
- w_i
- mass fraction of component i 1
- n_i, n_j
- amounts of the specified components mol
- V_solution
- total solution volume m^3
- m_solvent
- solvent mass kg
- m_i, m_j
- component masses kg
Conditions and scope
- Identify the components, solvent and temperature; denominators are positive.
- An analytical concentration of added material need not equal the free concentration of every reacting or associated species. A percentage needs its mass, volume or amount basis.
Sources · 3
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Paul Flowers, Klaus Theopold, Richard Langley and William R. Robinson · OpenStax/Rice University3 sources
- Chemistry 2e (2019), §3.3 MolarityPaul Flowers, Klaus Theopold, Richard Langley and William R. Robinson · OpenStax/Rice UniversityTextbook chapter
- Chemistry 2e (2019), §3.4 Other units for solution concentrationsPaul Flowers, Klaus Theopold, Richard Langley and William R. Robinson · OpenStax/Rice UniversityTextbook chapter
- Chemistry 2e (2019), §11.4 Colligative properties: mole fraction and molalityPaul Flowers, Klaus Theopold, Richard Langley and William R. Robinson · OpenStax/Rice UniversityTextbook chapter
Evidence and review
Inspected §3.3 amount/solution-volume definition, §3.4 mass percentage, and §11.4 mole-fraction, molality and temperature comparison paragraphs. Records SI units and basis explicitly; does not treat concentration as thermodynamic activity.
2026-10-10 · Independent Mathematics and Information editor (/root/core_math_information). Independent AI editorial review of this entry's statements, equations, applicability conditions and source coverage. Source checks apply to these claims within their stated limits.
Entry details
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- foundation-chem-concentration-scales
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