Chem 100L - Lecture on Titrations

Introduction

• Experiment Focus: Titrations
• Purpose: Using titration to determine the concentration (molarity) of an unknown acid or base.

Titration Setup

• Equipment: Burette (contains one compound), beaker/flask (contains another compound).
• Goal: Add one compound until stoichiometrically matched (both react completely to form product without remaining reactants).

Conceptual Understanding

• Stoichiometry: Analogous to a recipe (e.g., 2 bread: 1 cheese for a sandwich).
• Equivalence Point: Point where moles of acid equal moles of base, resulting in a neutral solution.

Acids and Bases

• Acids:
  • Characteristics: H⁺ ions, shown on the left-hand side of chemical formula.
  • Example: H₂SO₄ (sulfuric acid) - releases two H⁺ ions.
• Bases:
  • Characteristics: OH⁻ ions, end in OH (hydroxide ions).
  • Example: Sodium hydroxide (NaOH), potassium hydroxide (KOH).

Acid-Base Reactions

• Neutralization: H⁺ (from acid) and OH⁻ (from base) form water (neutral).

Titration Process

• Setup:
  • Base (OH⁻) in burette; Acid in flask.
  • Add base to acid until color change indicates reaction completion.
• Indicator: Phenolphthalein (clear in acid, pink in base) signals equivalence point.

Calculating Concentration

• Equation: Moles = Concentration (M) × Volume (L)
• At Equivalence Point: Moles of acid = Moles of base.
• Application: Rearrange equation to solve for unknown concentration.

Example Calculation

• Data Needed:
  • Volume of acid (known, e.g., 10 mL).
  • Volume of base added (determined by burette).
  • Concentration of base (from bottle).
• Equation: [ M_A = \frac{M_B \times V_B}{V_A} ]
• Units: Ensure consistency (e.g., mL for volumes).

Titration Steps

1. Coarse Titration: Initial run to estimate endpoint volume.
2. Fine Titration: Accurate, slow approach to equivalence point.

pH Meter

• Function: Measures acidity/basicity numerically.
• Scale: Neutral at pH 7; below 7 is acidic, above 7 is basic.

Data Documentation

• Record titration data for coarse and fine titrations.
• Calculations: Show work for determining acid concentration.

Conclusion

• Answer short questions, perform calculations, and note the postponed due date for experiment submission.