Overview
This video demonstrates a titration method to determine hydroxide ion concentration in a saturated calcium hydroxide solution using potassium hydrogen phthalate (KHP) solution and phenolphthalein indicator.
Objective
- Determine hydroxide ion concentration in saturated calcium hydroxide solution through titration
- Use titration data to calculate calcium hydroxide concentration
- Calculate the solubility product constant (Ksp) for calcium hydroxide
Materials Required
- Saturated calcium hydroxide solution (previously prepared)
- Burette charged with approximately 0.05 molar KHP solution
- Burette stand and clamp
- 50 milliliter graduated cylinder
- Erlenmeyer flask
- Phenolphthalein indicator
- Standard burette cleaning and charging equipment
Procedure
- Clean and charge burette with KHP solution following appropriate procedures
- Measure approximately 20 mL of saturated calcium hydroxide solution using graduated cylinder
- Transfer measured solution into Erlenmeyer flask
- Add 1-2 drops of phenolphthalein indicator to solution
- Solution turns vibrant fuchsia color upon indicator addition
- Record initial burette volume reading at meniscus eye level
- Position burette for titration with one hand controlling valve and other swirling flask
- Add KHP solution dropwise while continuously swirling
- Stop titration when fuchsia color becomes very faint or first disappears
- Record final burette volume at endpoint
Measurements and Data
| Parameter | Value | Units |
|---|
| Ca(OH)₂ solution volume | 19.9 | mL |
| Initial burette reading | 2.20 | mL |
| Final burette reading (endpoint) | 29.23 | mL |
| KHP volume used | 27.03 | mL |
| KHP concentration | ~0.05 | M |
Calculations and Analysis
- Volume of KHP used is known from burette readings
- Concentration of KHP solution is known from preparation
- Exact amount of KHP added can be calculated
- Hydroxide ion concentration determined from titration stoichiometry
- Calcium hydroxide concentration calculated from hydroxide concentration
- Solubility product constant (Ksp) determined from calcium hydroxide concentration
Key Terms & Definitions
- KHP (Potassium Hydrogen Phthalate): Primary standard acid used in titrations
- Phenolphthalein: pH indicator that is pink in basic solutions and colorless in acidic/neutral solutions
- Endpoint: Point in titration where indicator changes color signaling reaction completion
- Meniscus: Curved surface of liquid in graduated glassware
- Ksp (Solubility Product Constant): Equilibrium constant for dissolution of sparingly soluble ionic compound