(40) GCSE Chemistry Revision "Concentration of Solutions"

Understanding Concentration

• Definition of Concentration:

  • A measure of the mass of a solute in a given volume of solution.

  • For higher-tier students: an additional definition is available in future studies.

• Solute and Solvent:

  • A solute is a chemical that is dissolved in a solvent (commonly water).

  • The unit of concentration: grams per decimeter cubed (g/dm³).

  • Note: A decimeter cubed is equal to one liter, but the term "liter" is less commonly used in scientific contexts.

Calculating Concentration

• Concentration Formula:

  • Concentration (g/dm³) = Mass (g) / Volume (dm³)

  • Visual aid: A triangle can help to remember the relationship between mass, volume, and concentration.

• Example Calculation 1:

  • Problem: 200 grams of a chemical dissolved to a final volume of 1 dm³.

  • Solution:

    • Concentration = 200 g / 1 dm³ = 200 g/dm³.

More Challenging Calculations

• Example Calculation 2:

  • Problem: 150 grams of a chemical in 0.5 dm³.

  • Solution:

    • Concentration = 150 g / 0.5 dm³ = 300 g/dm³.

Rearranging the Concentration Equation

• Example Calculation 3:

  • Problem: Calculate mass needed for a concentration of 600 g/dm³ in a volume of 0.4 dm³.

  • Solution:

    • Mass = Concentration × Volume = 600 g/dm³ × 0.4 dm³ = 240 grams.

• Example Calculation 4:

  • Problem: Calculate final volume for 200 grams at a concentration of 800 g/dm³.

  • Solution:

    • Volume = Mass / Concentration = 200 g / 800 g/dm³ = 0.25 dm³.

Effects on Concentration for Higher Tier Students

• Effect of Changing Mass:

  • Increasing the mass of the solute (while keeping volume constant) increases concentration.

• Effect of Changing Volume:

  • Increasing the volume of the solution (while keeping mass of solute constant) decreases concentration.

Additional Resources

• More practice questions on concentration can be found in the revision workbook.