Lab Techniques

How to do a Manual Titration

Rinse the inside of the Burette

Rinse the burette with 2-3 mLs of standarized NaOH solution.

Make sure all inside walls including the tip are rinsed.

Fill the Burette

Discard the rinse solution into the sink or a “waste” beaker.

Close the stopcock, return the burette to the lab stand and fill with NaOH.

Take an Initial Reading

Make sure your eye is level with the meniscusbefore taking any readings.

meniscus

Reading the Burette

Read and record burette measurements with care.

Take all readings to 2 decimal places.

This burette is reading 24.28. The last digit is an estimate.

Rinse the Volumetric Pipet Use the rubber

pipet bulb to draw 2-3 mLs of the sample into the pipet.

Hold the pipet in a vertical position and tilt so the solution contacts all inside surfaces of the pipet.

Discard the Rinse Solution.

Pipet a 10.00 mL Sample

Use a rubber bulb to draw solution up into the volumetric pipet. The volume should be above the mark.

Use your index finger to control the level of the solution in the pipet.

When the bottom of the meniscus is at the mark, the volume is correct.

Transfer the Sample

Move the filled pipet to an erlenmeyer flask.

Release your finger and allow the liquid to drain on it’s own.

Touch the tip of the pipet to the side of the flask and remove the pipet.

Add an Indicator

Add 3-4 drops of phenol-phthalein indicator to each flask.

Use Proper Titration Techniques

Manipulate the burette stopcock with your left hand.

Hold and swirl the flask with your right hand.

Note: Instructions are for right handed persons. Do the reverse if left handed

Rinse Down the Flask

Use small amounts of distilled water to rinse down the sides of the flask from time to time, during the titration.

Aiming for Accuracy

As you near the endpoint add the NaOH dropwise then a fraction of a drop at a time.

To add a fraction of a drop, allow the drop to form on the tip of the burette then rinse it in with dist. Water.

Accuracy is how close your value is to the actual or known value.

Precision and Finishing

The titration is over when the solution becomes, and stays, a very pale pink.This is known as the “End Point” of the titration.

Precision is how close your values are to each other.

Aim for 3 samples to be within 1% of each other.