titration

What it is

• Titration is an experimental method used to determine the concentration of an unknown solution by reacting it with a solution of known concentration.
• It’s based on the principle of neutralization between an acid and an alkali.

Equipment list:

• Burette — measures variable volume of acid (or base) added.
• Pipette — measures fixed volume (usually 25.0 cm³) of solution of known concentration.
• Pipette filler — safely draws liquid into pipette.
• Conical flask — contains the solution being titrated.
• Clamp stand — holds the burette vertically.
• Funnel — used to pour acid/base into burette safely.
• Indicator — shows colour change at the end-point.

Common indicators

Titration Method:

1. Rinse the burette with water first, then with a small amount of the known solution. Fill the burette with the known solution and record the initial reading.
2. Rinse the pipette with water first, then with a small amount of the unknown solution. Use the pipette to transfer a measured volume (usually 25.0 cm³) of the unknown solution into a clean conical flask.
3. Add a few drops of indicator to the unknown solution.
4. Slowly run the known solution from the burette into the conical flask while swirling, until the endpoint is reached (when the indicator changes color).
5. Record the final burette reading. This is your rough titration.
6. Repeat the titration two to three more times carefully, adding the known solution drop by drop near the endpoint, until you get concordant results.

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Note:

• Known solution: concentration is known, can be acid or base.
• Unknown solution: concentration is what you are trying to find.
• Indicator: shows when the reaction is complete (endpoint).
• Concordant results: titrations that are within 0.1 cm³ of each other. </aside>

Calculations

1. Find moles of the known substance

   n = c × v

   (volume in dm³)

2. Use the balanced equation to find the ratio between acid and base.

3. Find the moles of the unknown substance using the ratio.

4. Find its concentration:

   C = $\frac{n}{V}$

Example:

Hydrochloric acid neutralises sodium hydroxide.

25.0 cm³ of NaOH requires 23.5 cm³ of 0.10 mol dm⁻³ HCl for neutralisation.

Find the concentration of NaOH.

1. Equation:

   HCl + NaOH → NaCl + H₂O

   Ratio = 1 : 1

2. Known moles of HCl:

   n = c × V

   n = 0.10 × (23.5 ÷ 1000) = 0.00235 mol

3. Moles of NaOH (1:1 ratio):

   n = 0.00235 mol

4. Concentration of NaOH:

   c = n / V = 0.00235 ÷ (25 ÷ 1000) = 0.094 mol dm⁻³

Accuracy tips

• No air bubbles in burette or pipette.
• Read the meniscus at eye level.
• Remove the funnel before titrating.
• Swirl flask continuously.
• Use white tile under flask to see colour change clearly.
• Repeat for concordant titres.

Safety

• Acids and bases are corrosive — wear goggles and rinse spills immediately.
• Use a pipette filler, not your mouth.
• Dispose of solutions as instructed.