Acid–Base Titration Lab

🧪 ONLYGYAANI CHEMISTRY VIRTUAL LAB

Acid–Base Titration

Titrate hydrochloric acid with sodium hydroxide. Control the burette, observe the pH and phenolphthalein colour, locate the equivalence region and calculate the concentration relationship.

🧪 HCl Analyte in flask
💧 NaOH Titrant in burette
🌸 Phenolphthalein Endpoint indicator
⚖️ 1 : 1 HCl : NaOH reaction
⚗️ Interactive Titration Apparatus
BURETTE READING 0.00 mL delivered BURETTE 0.100 M NaOH pH 1.00 ERLENMEYER FLASK 25.0 mL HCl + Indicator Acid in excess — continue titration
🎛 Titration Controls
Acid Volume 25.0 mL
HCl Concentration 0.100 M
NaOH Concentration 0.100 M
💧 Add NaOH Fine control near endpoint
NaOH Delivered 0.00 mL
Current pH 1.00
Equivalence Volume 25.00 mL
Indicator Colour Colourless
Acid Moles 0.00250 mol
NaOH Moles Added 0.00000 mol
Acid in excess.
Add NaOH from the burette.
🎯 Equivalence expected near 25.00 mL
Reaction
HCl + NaOH → NaCl + H₂O

At equivalence for this 1:1 reaction:
MacidVacid = MbaseVbase

🎯 Aim

To study the neutralization of hydrochloric acid with sodium hydroxide and determine the equivalence point using titration.

🧰 Apparatus

Burette, burette stand, conical flask, pipette, hydrochloric acid, sodium hydroxide and phenolphthalein indicator.

📘 Theory

Titration is a quantitative technique in which a solution of known concentration is added to another solution until the stoichiometric equivalence point is reached.

Balanced equation:

HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)
One mole of HCl reacts with one mole of NaOH.

⚖️ Equivalence Point

For this strong acid–strong base titration, equivalence occurs when the amount of NaOH added is stoichiometrically equal to the initial amount of HCl.

Default experiment:

HCl = 0.100 M × 0.0250 L
= 0.00250 mol

Required NaOH:
0.00250 mol ÷ 0.100 M
= 0.0250 L
= 25.00 mL

🌸 Phenolphthalein

Phenolphthalein is colourless in acidic and near-neutral solution and becomes pink in sufficiently basic solution.

During a practical titration, NaOH is added slowly near the endpoint. A faint persistent pink colour is commonly used as the phenolphthalein endpoint for this titration.
The indicator endpoint and the exact stoichiometric equivalence point are related but are not identical concepts.

📊 Observation Table

Trial HCl Volume HCl M NaOH M NaOH Added pH Colour Condition
No observations recorded.

🔬 Experiments to Try

Experiment 1
Use 25 mL of 0.100 M HCl and 0.100 M NaOH. Find the equivalence volume.
Experiment 2
Increase the HCl concentration and observe how much more NaOH is required.
Experiment 3
Increase the NaOH concentration and observe how the equivalence volume decreases.
Experiment 4
Add 0.05 or 0.10 mL portions near equivalence and observe the sharp pH change.

📝 Procedure

  1. Set the HCl volume and concentration.
  2. Set the NaOH concentration.
  3. Observe the calculated equivalence volume.
  4. Add NaOH from the virtual burette.
  5. Use larger additions while far from equivalence.
  6. Use 0.05–0.10 mL additions near the endpoint.
  7. Observe the pH and phenolphthalein colour.
  8. Record readings before and after equivalence.
  9. Compare experimental volume with the calculated equivalence volume.

⚠️ Precautions

Read a real burette at eye level from the bottom of the meniscus for a clear aqueous solution.
Add titrant slowly near the endpoint.
Swirl the flask during a real titration to mix the solutions.
Use suitable eye protection and laboratory procedures when handling acids and bases in a physical laboratory.

🎓 Quick Viva Questions

1. What is titration?

It is a quantitative analytical method in which one solution is added to another to determine a stoichiometric reaction point.

2. What is the reaction between HCl and NaOH?

HCl + NaOH → NaCl + H₂O.

3. What is the mole ratio of HCl to NaOH?

1 : 1.

4. What is the equivalence point?

It is the point at which acid and base have reacted in their exact stoichiometric proportions.

5. What is the pH at equivalence for an ideal strong acid–strong base titration at 25°C?

Approximately 7.

6. Why is NaOH added slowly near the endpoint?

Because the pH changes rapidly near equivalence, so a small excess of titrant can overshoot the desired endpoint.

7. What colour is phenolphthalein in acidic solution?

Colourless.

✅ Result

Hydrochloric acid is neutralized by sodium hydroxide in a 1:1 mole ratio. For the default experiment containing 25.0 mL of 0.100 M HCl, the stoichiometric equivalence volume is 25.00 mL of 0.100 M NaOH. The simulation also demonstrates the sharp pH change around the equivalence region.

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