Titrations and Titration Curves

Welcome to Chad's Prep, a resource for science courses including high school, college, MCAT, DAT, and OAT prep. This lesson is part of a general chemistry playlist focusing on titrations and titration curves.

Overview of Titrations

• Purpose: Determine the concentration of an acidic or basic species (analyte).
• Setup:
  • Analyte placed in an Erlenmeyer flask.
  • Titrant (standardized solution) added from a buret.
• Key Terms:
  • Analyte: Substance whose concentration is to be determined.
  • Titrant: Standardized solution used in titration.

Types of Titrations

1. Strong Acid-Strong Base Titrations

   • Example: HCl (acid) and NaOH (base).
   • Objective: Find the concentration of HCl.
   • Titration Curve: Initial low pH gradually increases; sharp rise at equivalence point.
   • Equivalence Point:
     • Moles of acid = Moles of base (NaOH = HCl).
     • Occurs when chemically equivalent amounts are added (1:1 ratio here).
     • Calculation: Molarity * Volume for both acid and base are equal at this point.
   • Indicator: Used to show the endpoint, often through color change (e.g., phenolphthalein).
   • Neutral Salt Formation: Results in pH 7 at the equivalence point.

2. Weak Acid-Strong Base Titrations

   • Example: HF (acid) and NaOH (base).
   • Titration Curve: Initial rapid pH change, then stabilizes.
   • Equivalence Point:
     • Moles of HF = Moles of NaOH.
     • pH > 7 due to formation of a basic salt (e.g., NaF).
   • Half Equivalence Point:
     • Occurs halfway to the equivalence point.
     • At this point, pH = pKa of the acid (e.g., HF).
     • Equilibrium between HF and its conjugate base F-.

3. Weak Base-Strong Acid Titrations

   • Example: NH3 (base) and HCl (acid).
   • Equivalence Point:
     • Moles of NH3 = Moles of HCl.
     • pH < 7 due to formation of an acidic salt (e.g., NH4Cl).
   • Half Equivalence Point:
     • At this point, pOH = pKb of the base (e.g., NH3).

Importance of Indicators

• Phenolphthalein: Changes color in the pH range of 6-8, ideal for strong acid-strong base titrations.
• Color Change: Indicates the endpoint, which approximates the equivalence point.
• Selection: Choose an indicator with a pKa close to the equivalence point pH.

Conceptual Summary

• Equivalence Point: Key for calculating unknown concentrations in titrations.
• Half Equivalence Point: Useful for determining pKa values for weak acids or pKb for weak bases.
• Hydrolysis: In some titrations, the salt formed undergoes hydrolysis affecting the pH.

Upcoming Lessons

• Detailed pH calculations for titrations of strong acid-strong base, weak acid-strong base, and weak base-strong acid.

Conclusion

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• Explore the General Chemistry Master Course for more practice.