Microscale titration | 11–16 years

This microscale practical involves uses simplified equipment and small quantities of chemicals to understand the basic principles of a titration.

Microscale titrations can be gravimetric (measuring the mass of the reaction vessel before and after) or volumetric (measuring the volume by counting the drops of solution added). Following integrated instructions, learners will carry out a simplified volumetric or gravimetric titration. 

Learning objectives

1. Make accurate observations for the end point of a titration.
2. Use your observations to infer what is happening during a titration.

Equipment (per group)

• 1 x beaker, 10 cm³ or small vial
• 1 x white tile
• 1 x clamp stand
• 1 x plastic pipette (preferably a fine-tipped pipette)
• 1 x measuring cylinder (10 cm³)
• 1 x mass balance (to 0.01 g)
• Vinegar solution (shop-bought, diluted by a factor of 4), 1 cm³
• Phenolphthalein solution (0.05%), 1 drop (WARNING: flammable)
• Sodium hydroxide solution (0.2 mol dm^-3), 10 cm³ (WARNING: irritant – skin and eyes)

Safety equipment

• Eye protection: safety glasses to EN166F

Health, safety and technical notes

• Read our standard health and safety guidance and carry out a risk assessment before running any live practical.
• Refer to SSERC/CLEAPSS Hazcards and recipe sheets.
• Hazard classification may vary depending on supplier.

 Read the technician notes for full safety information, preparation and disposal. 

Method

Gravimetric titration

1. Add 1 drop of phenolphthalein to the small beaker and record its mass.
2. Using a measuring cylinder, measure out 1 cm³ of diluted vinegar and add it to the beaker. Record its mass.
3. Fill the plastic pipette with NaOH solution and clamp it gently.
4. Place the beaker below the pipette.
5. Carefully tighten the clamp to add one drop of NaOH solution to the beaker at a time.
6. Swirl the beaker.
7. Add NaOH solution dropwise until a permanent pink colour is formed.
8. Record the mass of the beaker.

Volumetric titration

1. Add 1 drop of phenolphthalein to a small beaker or vial.
2. Add ~1 cm³ of vinegar to the same beaker.
3. Fill a dropping pipette with sodium hydroxide solution (around 0.2 M).
4. Clamp the pipette gently.
5. Tighten the clamp carefully until 1 drop of NaOH is added to the beaker/vial.
6. Swirl the beaker/vial.
7. Repeat steps 5 and 6 (counting the number of drops added) until a pale permanent pink colour is seen.

Disposal

Rinse the aqueous solutions down a foul-water drain with plenty of water.