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Guilherme Mazui

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What is the Difference Between Molarity and Molality?

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Molarity and molality are both measures of a chemical solution's concentration, but they differ in terms of mass and volume. The primary difference between the two is:

  • Molarity: It is the ratio of moles of a solute to the volume of a solution, typically expressed in liters. The formula for molarity is M = moles of solute / volume of solution in liters. Molarity is denoted by the letter M and its units are M or mol/L.
  • Molality: It is the ratio of moles of a solute to the mass of a solvent, typically expressed in kilograms. The formula for molality is m = moles of solute / mass of solvent in kilograms. Molality is denoted by the letter m and its units are m or mol/kg.

Some key differences between molarity and molality include:

  1. Molarity is affected by changes in temperature, volume, and pressure of the solvent, while molality is unaffected by these factors.
  2. In clinical settings, doctors and nurses usually work with molarity because it is easier to understand and use. In contrast, laboratory settings often use molality for its precision and independence from temperature and pressure changes.
  3. Molarity is more commonly used in the medical field, while molality is more commonly used in lab settings.
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  • What is the Difference Between Molarity and Molality?
  • Comparative Table: Molarity vs Molality

    • Comparative Table: Molarity vs Molality

    Here is a table comparing the differences between molarity and molality:

    Property Molarity Molality
    Definition Molarity is the number of moles of a solute per liter of solution. Molality is the number of moles of a solute per kilogram of solvent.
    Formula M = Number of moles of the solute/Volume of the solution in liters. m = Number of moles of the solute/Mass of the solution in liters.
    Units Molarity is expressed in units of M or mol/L. Molality is expressed in units of m or mol/kg.
    Temperature Dependence Molarity is affected by changes in temperature. Molality is unaffected by changes in temperature.
    Volume Dependence Molarity depends on the volume of the solution. Molality depends on the mass of the solvent.
    Preferred Usage Molarity is useful for practical laboratory testing, but errors from volume estimation can be greater than errors from a molality balance. Molality is preferred for concentration transmission due to its independence from temperature and volume, making it more accurate.
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    Guilherme Mazui

    Guilherme Mazui is graduated in journalism from the Federal University of Minas Gerais (UFMG) and a master's degree in Communication from the University of São Paulo (USP). In addition, he has experience in advertising writing and has worked as a content editor in several companies.