Lecture Notes: Concentration of Solutions

Key Concepts

• Concentration: A measure of the number of solute particles in a solvent.
• Concentrated vs. Dilute Solutions:
  • A concentrated solution contains more solute particles than a dilute solution.
  • Example: Adding more sugar to a drink increases its sweetness, indicating a higher concentration.

Calculating Concentration

There are two primary methods for calculating the concentration of a solution:

1. Using Moles

• Formula: Concentration = Moles / Volume
• Volume Measurement: Usually in cubic centimetres (cm³) or litres (dm³).
  • Conversion: 1000 cm³ = 1 dm³ (1 litre).
  • Example Conversion: 500 cm³ = 0.5 dm³.
• Formula Triangle Method:
  • Cover the quantity you need to find:
    • To find moles: Multiply concentration by volume.
    • To find concentration: Divide moles by volume.
• Example Calculation:
  • 2 moles of salt in 2 litres of water.
  • Concentration = 2 moles / 2 litres = 1 mole per dm³.

2. Using Mass

• Formula: Concentration = Mass / Volume
• Unit: Grams per dm³ instead of moles per dm³.
• Formula Triangle: Similar to moles, can be used to calculate any quantity.
• Example Challenge:
  • Desired concentration: 10 g/dm³.
  • Volume: 250 cm³ (convert to 0.25 dm³).
  • Calculate the mass needed based on the desired concentration.

Summary

• Two Methods of Concentration Calculation:
  • Using moles of the solute.
  • Using mass of the solute.
• Key Methodology:
  • Divide the amount of solute (moles or mass) by the volume of the solution.
  • Use formula triangles to easily calculate missing quantities through multiplication or division.

Remember to always include units when calculating concentration to ensure clarity and accuracy in your results.