Titration Question (Copy)
📘 1. What is a Titration?
Titration is a volumetric analysis technique used to determine:
- The concentration of an unknown acid or alkali
- The exact volume of acid needed to neutralize a base (or vice versa)
🧪 2. Standard Titration Setup – Diagram and Labels
Always include and label:
- Burette (fixed vertically in clamp stand)
- Pipette (usually 25.0 cm³) + pipette filler
- Conical flask (holds measured alkali/acid)
- White tile (to see color change clearly)
- Indicator (phenolphthalein/methyl orange)
- Clamp stand + retort stand
- Beaker for rinsing
📌 Common Labels for ATP Diagrams:
- “Burette filled with dilute hydrochloric acid”
- “Conical flask containing sodium hydroxide solution + phenolphthalein”
- “White tile placed under conical flask for visibility of color change”
🧪 3. Step-by-Step Titration Method (Use this in planning questions)
1. Rinse Equipment:
- Rinse pipette with alkali solution (e.g., NaOH)
- Rinse burette with acid (e.g., HCl)
- Rinse conical flask with distilled water
2. Fill Equipment:
- Use a pipette and filler to transfer 25.0 cm³ of alkali to conical flask
- Add 2–3 drops of indicator to the conical flask
- Fill burette with acid up to 0.00 cm³ mark and remove air bubbles
3. Perform Titration:
- Place conical flask on white tile
- Open burette tap slowly, swirling flask continuously
- Watch for permanent color change (end point)
- Record final volume from burette
4. Repeat and Average:
- Perform at least 3 concordant results (within 0.10 cm³)
- Calculate average volume used (ignore rough trial)
🌈 4. Choice of Indicator Based on Acid/Base Strength
| Acid + Base Type | Indicator | Color Change at End Point |
|---|---|---|
| Strong acid + Strong base | Phenolphthalein or Methyl Orange | Pink → Colorless or Orange → Yellow |
| Strong acid + Weak base | Methyl Orange | Orange → Red |
| Weak acid + Strong base | Phenolphthalein | Colorless → Pink |
❗ Use the indicator recommended in the question — don’t assume.
📊 5. Recording Burette Readings (Data Table Questions)
Rules for Data Table in ATP:
- Record initial and final burette readings to 2 decimal places
- e.g., 24.30 cm³ not 24.3
- Subtract to get volume of acid used (titre)
- Do not record “rough” trial in final average
Sample Table:
| Trial No. | Initial (cm³) | Final (cm³) | Volume Used (cm³) |
|---|---|---|---|
| Rough | 0.00 | 24.70 | 24.70 |
| 1 | 0.00 | 24.40 | 24.40 |
| 2 | 0.00 | 24.30 | 24.30 |
| 3 | 0.00 | 24.35 | 24.35 |
✔️ Average volume = (24.30 + 24.35 + 24.40) / 3 = 24.35 cm³
📐 6. Typical Calculation Question Types
A. Calculate Number of Moles
Use:
moles = (volume in cm³ / 1000) × concentration (mol/dm³)
B. Find Unknown Concentration
Rearrange:
concentration = moles / volume (in dm³)
C. Use Balanced Equation
Example:
If HCl + NaOH → NaCl + H₂O
Then mole ratio = 1:1
Example Titration Calculation:
25.0 cm³ of NaOH was titrated with 0.100 mol/dm³ HCl.
Average volume of acid used = 24.35 cm³.
Find the concentration of NaOH.
Step 1: Moles of HCl used
= (24.35 / 1000) × 0.100 = 0.002435 mol
Step 2: Mole ratio (NaOH:HCl = 1:1)
Moles of NaOH = 0.002435 mol
Step 3: Concentration of NaOH
= moles / (25.0 / 1000) = 0.002435 / 0.025 = 0.0974 mol/dm³
✔️ Final answer: 0.097 mol/dm³ (3 sf)
🧼 7. Common Titration Mistakes in ATP
| Mistake | Why It’s Wrong | Correction |
|---|---|---|
| Burette or pipette drawn without labels | Incomplete diagram | Label volumes + substances clearly |
| Using inconsistent decimal places | Marks lost | Record all volumes to 2 decimal places |
| Averaging rough result | Invalidates accuracy | Only average concordant accurate trials |
| Wrong color change | Indicates weak theoretical understanding | Memorize correct indicator color shifts |
| Final volume less than initial | Impossible unless burette is upside down | Always subtract initial from final |
| No rinsing of apparatus | Poor technique | Rinse each item with its respective liquid before use |
🧠 8. Tips to Maximize Marks in Titration Questions
- Always show full working for calculations
- Don’t abbreviate chemicals: write “hydrochloric acid”, not HCl (unless clearly instructed)
- Use appropriate significant figures (usually 3 sf)
- When planning: include rinsing, swirling, white tile, indicator choice, and repetition
- Label burette readings as “Initial” and “Final”, not just numbers
- If color change is asked, say:
→ “pink to colorless” (phenolphthalein)
→ “orange to red” (methyl orange)