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3.4 Other Units for Solution Concentrations

3 min read•june 24, 2024

Solution concentration units are essential for describing the amount of solute in a solution. From to , these units help chemists quantify and communicate solution compositions accurately.

Understanding these units and how to convert between them is crucial for various applications. Whether working in a lab or analyzing environmental samples, mastering solution concentration units is key to success in chemistry.

Solution Concentration Units

Mass percentage, volume percentage, and mass-volume percentage as solution concentration units

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  • (% w/w) represents the ratio of solute mass to total solution mass multiplied by 100%
    • Calculated using the formula: Mass percentage=Mass of soluteMass of solution×100%\text{Mass percentage} = \frac{\text{Mass of solute}}{\text{Mass of solution}} \times 100\%
    • Commonly used for solid-solid or solid-liquid solutions (salt in water)
  • (% v/v) represents the ratio of solute volume to total solution volume multiplied by 100%
    • Calculated using the formula: \text{[Volume percentage](https://www.fiveableKeyTerm:Volume_Percentage)} = \frac{\text{Volume of solute}}{\text{Volume of solution}} \times 100\%
    • Commonly used for liquid-liquid solutions (ethanol in water)
  • (% w/v) represents the ratio of solute mass to total solution volume multiplied by 100%
    • Calculated using the formula: Mass-volume percentage=Mass of soluteVolume of solution×100%\text{Mass-volume percentage} = \frac{\text{Mass of solute}}{\text{Volume of solution}} \times 100\%
    • Commonly used for solid-liquid solutions (glucose in saline)
    • Frequently used in medical and pharmaceutical settings (antibiotics, intravenous fluids)

Parts-per-million and parts-per-billion

  • (ppm) represents the ratio of solute mass or volume to total solution mass or volume multiplied by 1,000,000
    • Calculated using the formula: ppm=Mass or volume of soluteMass or volume of solution×1,000,000\text{ppm} = \frac{\text{Mass or volume of solute}}{\text{Mass or volume of solution}} \times 1,000,000
    • 1 ppm is equivalent to 1 mg/L or 1 mg/kg
    • Used for very dilute solutions (contaminants in drinking water, pesticides in food)
  • (ppb) represents the ratio of solute mass or volume to total solution mass or volume multiplied by 1,000,000,000
    • Calculated using the formula: ppb=Mass or volume of soluteMass or volume of solution×1,000,000,000\text{ppb} = \frac{\text{Mass or volume of solute}}{\text{Mass or volume of solution}} \times 1,000,000,000
    • 1 ppb is equivalent to 1 μg/L or 1 μg/kg
    • Used for extremely dilute solutions (trace contaminants in air, toxic substances in soil)

Mole-based concentration units

  • represents the number of moles of solute per liter of solution
    • Calculated using the formula: Molarity=Moles of soluteLiters of solution\text{Molarity} = \frac{\text{Moles of solute}}{\text{Liters of solution}}
    • Commonly used in laboratory settings and chemical reactions
  • (m) represents the number of moles of solute per kilogram of solvent
    • Calculated using the formula: Molality=Moles of soluteKilograms of solvent\text{Molality} = \frac{\text{Moles of solute}}{\text{Kilograms of solvent}}
    • Used when temperature changes affect solution volume
  • represents the ratio of moles of a component to the total moles of all components in a solution
    • Calculated using the formula: Mole fraction of A=Moles of ATotal moles of all components\text{Mole fraction of A} = \frac{\text{Moles of A}}{\text{Total moles of all components}}
    • Used in thermodynamic calculations and vapor pressure studies
  • (N) represents the number of equivalents of solute per liter of solution
    • Calculated using the formula: Normality=Equivalents of soluteLiters of solution\text{Normality} = \frac{\text{Equivalents of solute}}{\text{Liters of solution}}
    • Used in acid-base titrations and redox reactions

Conversion of concentration units

  • Converting molarity to mass percentage:
    1. Convert molar mass of solute to grams per liter (g/L)
    2. Divide solute mass by solution density to obtain mass fraction
    3. Multiply mass fraction by 100% to get mass percentage
  • Converting mass percentage to molarity:
    1. Convert mass percentage to mass fraction by dividing by 100%
    2. Multiply mass fraction by solution density to obtain solute mass per liter (g/L)
    3. Divide solute mass per liter by molar mass of solute to get molarity
  • Converting volume percentage to molarity:
    1. Convert volume percentage to volume fraction by dividing by 100%
    2. Multiply volume fraction by solute density to obtain solute mass per liter (g/L)
    3. Divide solute mass per liter by molar mass of solute to get molarity
  • Converting molarity to parts-per-million (ppm) or parts-per-billion (ppb):
    1. Convert molarity to grams per liter (g/L) by multiplying by molar mass of solute
    2. Multiply grams per liter by 1,000 to obtain milligrams per liter (mg/L) for ppm, or by 1,000,000 to obtain micrograms per liter (μg/L) for ppb

Key Terms to Review (15)

Mass percentage: Mass percentage is a way to express the concentration of a component in a mixture. It is calculated as the mass of the component divided by the total mass of the mixture, multiplied by 100%.
Mass Percentage: Mass percentage, also known as weight percentage, is a measure of the relative amount of a substance in a mixture or solution, expressed as the mass of the substance divided by the total mass of the mixture, multiplied by 100. It is a common way to describe the concentration of a solution in the context of 3.4 Other Units for Solution Concentrations.
Mass-Volume Percentage: Mass-volume percentage, also known as mass/volume percentage or m/v%, is a unit of concentration that expresses the mass of a solute dissolved in a given volume of solution. It represents the ratio of the mass of the solute to the total volume of the solution, typically expressed as a percentage.
Molality: Molality is a measure of the concentration of a solution, defined as the number of moles of a solute dissolved per kilogram of solvent. It is a useful unit for describing the composition of solutions, especially when the density of the solution is not well-known or when the volume of the solution changes with temperature.
Molarity: Molarity is a measure of the concentration of a solution, specifically the number of moles of a solute dissolved per liter of solution. It is a fundamental concept in chemistry that is used to quantify the amount of a substance present in a given volume of a solution and is essential for understanding various chemical processes and analyses.
Molarity (M): Molarity (M) is a measure of the concentration of a solute in a solution, expressed as moles of solute per liter of solution. It is commonly used to quantify the concentration of chemical solutions in laboratory settings.
Mole Fraction: The mole fraction is a dimensionless quantity that represents the ratio of the amount of a particular substance to the total amount of all substances present in a mixture. It is a useful concept in understanding the composition of solutions, gaseous mixtures, and the behavior of colligative properties.
Mole fraction (X): Mole fraction (X) is a dimensionless quantity that represents the ratio of moles of a component to the total moles in a mixture. It is used to express the concentration of each component in gaseous mixtures.
Normality: Normality is a measure of the concentration of a solution that expresses the number of equivalents of a solute per liter of solution. It is commonly used in acid-base reactions, precipitation reactions, and other chemical processes where the reactivity of a substance is important.
Parts per billion (ppb): Parts per billion (ppb) is a unit of measurement used to express the concentration of one substance in a solution. It denotes one part of solute per billion parts of the total solution.
Parts per million (ppm): Parts per million (ppm) is a unit of concentration that denotes the number of parts of a substance in one million parts of the total solution. It is commonly used to measure very dilute concentrations.
Parts-per-billion: Parts-per-billion (ppb) is a unit of measurement used to express extremely low concentrations of a substance in a solution or mixture. It represents the number of units of a particular substance per one billion units of the overall solution.
Parts-Per-Million: Parts-per-million (ppm) is a unit of measurement used to express the concentration of a substance in a solution or mixture. It represents the number of units of a particular substance for every one million units of the total solution or mixture.
Volume percentage: Volume percentage is a way to express the concentration of a component in a mixture, defined as the volume of the solute divided by the total volume of the solution, multiplied by 100%. It is commonly used for solutions where both solute and solvent are liquids.
Volume Percentage: Volume percentage, also known as volume fraction, is a measure of the relative volume of a component in a mixture or solution. It is expressed as the ratio of the volume of a specific component to the total volume of the mixture, typically represented as a percentage.
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