Concentration of Solutions

Key Concepts

• Concentration: Measure of the number of particles of a solute in a solvent.
• Concentrated Solution: Has more particles of solute compared to a dilute solution.
• Dilute Solution: Has fewer particles of solute compared to a concentrated solution.

Example: Sweetening a Drink

• Adding more sugar (solute) to a drink (solvent) increases sweetness, demonstrating increasing concentration.

Calculating Concentration

Formula Using Moles

• Concentration (C) can be calculated by dividing the number of moles (n) of solute by the volume (V) of the solution.
• Formula: ( C = \frac{n}{V} )
• Units: Moles per cubic decimetre (mol/dm³)

Example Calculation

• Volume Conversion: 1000 cm³ = 1 dm³ (1 litre)
• Conversion Example: 500 cm³ = 0.5 dm³
• Example Problem: With 2 moles of solute in 2 liters of solution:
  • ( C = \frac{2 \text{ moles}}{2 \text{ litres}} = 1 \text{ mol/dm}^3 )

Formula Using Mass

• Sometimes, concentration is calculated using the mass (m) of the solute.
• Formula: ( C = \frac{m}{V} )
• Units: Grams per cubic decimetre (g/dm³)

Example Calculation

• Given: Desired concentration = 10 g/dm³, Solution volume = 250 cm³
• Volume Conversion: 250 cm³ = 0.25 dm³
• To find mass (m):
  • Use the triangle to rearrange: ( m = C \times V )
  • ( m = 10 \text{ g/dm}^3 \times 0.25 \text{ dm}^3 = 2.5 \text{ grams} )

Formula Triangle Method

• Cover up the quantity you want to find in the triangle to determine which operation to use (multiplication or division).
• Useful for both moles and mass concentration calculations.

Summary

• Two ways to calculate concentration:
  1. Using moles (amount of substance).
  2. Using mass (grams of substance).
• Both methods require division by the volume of the solution.
• Formula triangles are helpful tools for calculating unknowns by covering the desired variable and using appropriate operations.