Titration Lecture Notes

Introduction

• Discussion on titration involving a strong acid and a strong base.
• Starting with 20 mL of 0.500 molar HCl (strong acid).
• Adding a 0.500 molar solution of NaOH (strong base).
• The pH increases as the base is added, illustrated on a titration curve.

Titration Curve Overview

• Y-axis: pH
• X-axis: Volume of base added

Part A: pH Before Adding Base

• Initial condition: 0.0 mL of NaOH added.
• Only HCl (acid) is present.
• HCl ionization: 100% as it is a strong acid.
  • Reaction: HCl donates a proton to H2O forming H3O⁺ and Cl⁻.
• Initial concentration: 0.500 molar HCl
  • Equals to 0.500 molar H3O⁺ due to full ionization.
• pH Calculation:
  • pH = -log[H3O⁺]
  • Calculation: -log(0.500) = 0.301
• Titration Curve Point: At 0.0 mL of base, pH is 0.301

Adding 10 mL of Base

• Objective: Find pH after adding 10 mL of NaOH.
• Neutralization Reaction: Hydroxide ions (OH⁻) neutralize hydronium ions (H3O⁺).
• Calculation of moles:
  • H3O⁺: 0.500 molar * 0.02 L = 0.01 moles
  • OH⁻: 0.500 molar * 0.01 L = 0.005 moles
• Reaction Outcome:
  • Complete reaction of OH⁻ with H3O⁺
  • Remaining moles of H3O⁺ = 0.01 - 0.005 = 0.005 moles
  • Half of the acid has been neutralized.
• New Concentration of H3O⁺:
  • Volume increased to 30 mL (0.03 L)
  • Concentration = 0.005 moles / 0.03 L = 0.17 molar
• pH Calculation:
  • pH = -log(0.17) = 0.77
• Titration Curve Point: At 10 mL of base, pH is 0.77

Next Steps

• Continue analyzing the titration curve in the subsequent lecture.