Section 4.5: Dilutions of Solutions

Key Concepts

• Stock Solution: A concentrated solution from which a diluted solution can be prepared.
• Dilution Process: The method of preparing a diluted solution by adding solvent to a concentrated solution. The amount of solute remains constant.

Important Formula

• Number of Moles (n): n = concentration (C) × volume (V)
• Dilution Equation: C1 × V1 = C2 × V2
  • C1: Concentration of stock solution
  • V1: Volume of stock solution
  • C2: Concentration of diluted solution
  • V2: Volume of diluted solution

Example Calculations

1. Example 1: Diluting HCl

   • Goal: Prepare 1.50 L of 0.2 M HCl from a 12 M stock solution.
   • Formula Application: 12 × V1 = 0.2 × 1.5
   • Solution: V1 = 0.025 L or 25 mL

2. Example 2: Diluting KOH

   • Goal: Prepare 500 mL of 0.2 M KOH from 50 mL of stock solution.
   • Formula Application: C1 × 0.05 = 0.2 × 0.5
   • Solution: C1 = 2 M

Dilution Factor

• Definition: The factor by which a stock solution is diluted.
• Calculation Methods:
  1. Volume-based: Dilution Factor = Volume of Final Solution / Volume of Initial Solution
  2. Concentration-based: Dilution Factor = Concentration of Initial Solution / Concentration of Final Solution
• Example: 20 mL stock solution diluted to 50 mL
  • Dilution Factor: 50 / 20 = 2.5

Practical Example with Dilution Factor

• Example: Preparing NaCl solution
  • Goal: Obtain 100 mL of a solution diluted 50 times from a 0.5 M stock solution.
  • Formula Application: V_initial = V_final / Dilution Factor = 100 / 50
  • Solution: 2 mL

Important Notes

• The concentration of the solute in the stock solution does not affect the volume calculation for dilution when using the dilution factor method.