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The Concentration of Solutions: Molarity and Molality

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Concentration of Solutions

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Lesson Focus

The Concentration of Solutions: Molarity and Molality


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You will discover how concentrations of various substances are calculated. Learners also observe how the changes in mass and volume within a solution can affect these ratios.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • Define molarity as the number of moles of solute divided by the liters of solution.
  • Define molality as the number of moles of solute divided by the kilograms of solvent.
  • Calculate the number of moles of a solute or its mass when given the molar mass of the solute, the volume of the solution, or the mass of the solvent.
  • Solve molarity problems.
  • Solve molality problems.

Everything You'll Have Covered

Molarity and molality are quantitative measurements of a solution's concentration. A qualitative approach to measuring concentration such as taste may not be safe because of the potential toxicity of chemicals. Molarity assesses how much solute is dissolved in a solution. It is measured in moles of solute per liter of solution. A one-molar solution is defined as one that contains one mole of substance in each liter of the solution. It is prepared by dissolving one mole of substance in the solvent and diluting it to a final volume of one liter in a volumetric flask. Molality is also a measurement of a solution's concentration. It is measured in moles of solute per kilogram of solvent. Mass is a measurement that is independent of temperature. Volume, on the other hand, is a measurement that fluctuates with changes in temperature. A change in temperature will change the measurement of molarity. Thus, molality is a more accurate means to measure a solution's concentration.

Tutorial Details

Approximate Time 20 Minutes
Pre-requisite Concepts Learners should be familiar with molar mass and moles.
Course Chemistry
Type of Tutorial Problem Solving
Key Vocabulary chemistry, concentration, mass