Acid-base titrations (volumetric analysis)

1. What is a Titration?

• Titration is a technique used to determine the concentration of an unknown acid or base.
• It involves adding a solution of known concentration (titrant) to a solution of unknown concentration until neutralisation occurs.
• When used to determine concentration, it is called volumetric analysis.

2. Apparatus for an Acid-Base Titration

Essential Equipment:

• Burette (contains the titrant – solution of known concentration).
• Pipette (used to transfer a fixed volume of the unknown solution).
• Conical Flask (where the reaction takes place).
• Indicator (to show the endpoint of the reaction).

3. Step-by-Step Method for an Acid-Base Titration

Step 1: Prepare the Flask

• Rinse the conical flask with distilled water.
• Use a pipette to transfer a fixed volume of the unknown solution (acid or base) into the flask.
• Add a few drops of indicator to the flask.

Step 2: Set Up the Burette

• Rinse the burette with some of the titrant (solution of known concentration).
• Fill the burette carefully and remove air bubbles.
• Record the initial burette reading.

Step 3: Add the Titrant Slowly

• Slowly add the titrant from the burette while swirling the flask.
• Continue until the indicator changes colour permanently (this is the endpoint).

Step 4: Record and Calculate

• Record the final burette reading.
• Determine the volume of titrant added by subtracting the initial reading from the final reading.
• Use the titration formula to calculate the unknown concentration:

$C_1V_1 = C_2V_2$

where:

• $C₁, V₁ =$ concentration and volume of the acid
• $C₂, V₂ =$ concentration and volume of the base

4. Indicators Used in Titrations

Titration Type	Expected Endpoint pH	Best Indicator	Colour Change
$Strong Acid + Strong Base$	pH ~ 7	Bromothymol Blue	$Yellow → Blue$
$Strong Acid + Weak Base$	pH < 7	Methyl Orange	$Red → Yellow$
$Weak Acid + Strong Base$	pH > 7	Phenolphthalein	$Colourless → Pink$

5. Key Points to Remember

✅ The endpoint is reached when the indicator changes colour permanently.

✅ Always rinse the burette and pipette with the solution to be used.

✅ Swirl the flask continuously while adding the titrant.

✅ Record burette readings to two decimal places.

✅ The correct indicator must be used depending on the acid-base strength.