Glassware Conditioning: A burette must never be filled directly if wet with distilled water. Always click Rinse first to condition with titrant solution.
Air Bubbles: Ensure the burette tip has no trapped air. The virtual rinse step simulates purging the tip.
Eye Level Reading: Always read the meniscus at eye level to avoid parallax error.
2. Standard Titration Procedure
Rinse: Click Rinse button (turns green when complete)
Fill: Click Fill Burette
Initial Reading: Click burette to open magnifier, record exact initial volume
Stirring: Enable Stirrer for continuous mixing
Coarse Addition: Use stopcock slider for bulk titrant delivery
Fine Addition: Near endpoint, use + Drop button for precise control
Endpoint Detection: Watch for permanent color change
Final Reading: Click burette again to record final volume
Log Trial: Click Log Trial to save data
3. Reading the Meniscus
The meniscus is the curved liquid surface. Always read from the bottom of the meniscus at eye level. The magnified view allows precision to ±0.01 mL (two decimal places).
⚠️ Precision Rules:
Burette readings: record to 0.01 mL (e.g., 23.45 mL)
Calculate titre by subtraction: Final - Initial
Report titre to 0.01 mL precision
Multiple trials should be concordant (within 0.10 mL of each other)
4. Stoichiometry & Calculations
The general formula for titration calculations:
n(analyte) = n(titrant) × (stoichiometric ratio)
C(analyte) = [C(titrant) × V(titre) × stoich(analyte)] /
[V(analyte) × stoich(titrant)]
Where:
- C = concentration (M)
- V = volume (mL or L, must be consistent)
- stoich = stoichiometric coefficient from balanced equation
Example: Strong Acid-Base (1:1 Stoichiometry)
HCl + NaOH → NaCl + H₂O
Given:
- V(HCl) = 25.00 mL
- C(NaOH) = 0.1000 M
- V(titre) = 23.45 mL
Calculation:
C(HCl) = (0.1000 M × 23.45 mL × 1) / (25.00 mL × 1)
= 0.0938 M
Indicator: Self-indicating (permanganate is purple)
Endpoint: First excess drop turns solution pale pink
Calculation: C(Fe²⁺) = [C(MnO₄⁻) × V × 5] / V(Fe²⁺)
Iodometry (Na₂S₂O₃ vs I₂)
Stoichiometry: 2 S₂O₃²⁻ : 1 I₂
Equation: 2S₂O₃²⁻ + I₂ → S₄O₆²⁻ + 2I⁻
Indicator: Starch (forms blue I₂-starch complex)
Technique: Add starch when solution turns pale yellow
Endpoint: Blue color disappears completely (colorless)
Complexometric: EDTA vs Mg²⁺ and Zn²⁺
Key differences from Ca²⁺:
Mg²⁺: Smaller stability constant (Kf = 4.9×10⁸ vs Ca²⁺ 5×10¹⁰). Less sharp equivalence. Requires pH 10 NH₃/NH₄Cl buffer.
Zn²⁺: Very large Kf (3.2×10¹⁶). Extremely sharp equivalence. Can use Xylenol Orange indicator at pH 5-6.
EBT Indicator: Wine-red when metal is complexed, pure blue when free.
Equation: M²⁺ + EDTA⁴⁻ → [M-EDTA]²⁻ (1:1 always)
Back Titration (HCl + CaCO₃)
Concept: When a substance cannot be titrated directly (e.g., insoluble solid like CaCO₃), a known excess of a reagent (HCl) is added. The unreacted excess is then back-titrated with a standard solution (NaOH).