Lab Techniques

1
Lab Techniques

• How to do a Manual Titration

2
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.

3
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.

4
Take an Initial Reading

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

meniscus
5
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.

6
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.

7
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.

8
Transfer the Sample

• Move the filled pipet to an erlenmeyer flask.
• Release your finger and allow the liquid to drain
  on its own.
• Touch the tip of the pipet to the side of the
  flask and remove the pipet.

9
Add an Indicator
Add 3-4 drops of phenol-phthalein indicator to
each flask.
10
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
11
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.

12
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.
13
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.