Lecture Notes: Molarity and Dilution Calculations

Key Topics

• Dilution Process
• Dilution Equation
• Example Problem

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Dilution Process

• Definition: Dilution is the process of decreasing the concentration of a solution by adding more solvent.
• Common Practice: In chemistry, stock solutions are often more concentrated and diluted for future use.
• Purpose: To prepare solutions of desired concentrations by adding solvent to a concentrated stock solution.

Example of Dilution

• Two solutions with the same mass of copper:
  • The more dilute solution has a larger volume as the copper nitrate is dissolved in more solvent.

Molarity and Volume Relationship

• Formula: Number of moles = Molarity × Volume (in liters)
  • Molarity is in moles per liter.
  • Volume in liters, allowing liters to cancel out, leaving moles.

Equation Representation

• For solutions before (N1) and after (N2) dilution:
  • Key Principle: The dilution process does not change the amount of solute.
  • Equality: N1 = N2, meaning the number of moles before and after dilution is equal.

Dilution Equation

• General Equation: C1V1 = C2V2
  • C1: Initial concentration
  • V1: Initial volume
  • C2: Final concentration
  • V2: Final volume
• Application: Can be used with any concentration or volume units.

Example Problem

• Given: 0.850 liters of a 5 molar copper nitrate solution diluted to 1.8 liters.
• Find: Final molarity (C2)
• Solution:
  • Rearrange equation: C2 = (C1V1) / V2
  • Substitute values:
    • C1 = 5 molar
    • V1 = 0.850 liters
    • V2 = 1.80 liters
  • Calculate: C2 = 2.36 molar

Flexibility of the Dilution Equation

• The equation can solve for any of the four variables (C1, V1, C2, V2):
  • Example Uses:
    • To find the volume needed for a desired final concentration
    • To determine the volume of stock solution needed (V1)
• Utility: Highly versatile for various dilution calculations.