Lab Techniques How to do a Manual Titration

Rinse and Fill the Burette • Rinse the Burette with 2 -3 m. L of standardized Na. OH solution. • Make sure all inside walls including the tip are rinsed. • Discard the rinse solution into the sink or a “waste” beaker. • Close the stopcock, return the burette to the lab stand fill with Na. OH.

Reading the Burette • Make sure your eye is level with the meniscus before taking any readings. • 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 m. Ls 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 m. L 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 phenolphthalein 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 Na. OH 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.