How to use a Burette and Volumetric Pipettes

Volumetric Pipettes

1. Volumetric pipettes labeled TD (to deliver) at the upper end are designed to deliver the volume stated on the pipette. There will always be a small amount of liquid inside the tip after pipetting. If this liquid is blown out you will have delivered slightly more than the designed capacity of the pipette. Almost all of our pipettes are TD pipettes. However, other types do exist: Pipettes labeled TC (to contain) are designed to contain the volume stated on the pipette. Therefore, all liquid on a TC pipette should be expelled to obtain the desired volume.
2. If a drop of liquid hangs on the outside tip of the pipette the pipette tip should be dipped into the solution that has been pipetted to remove this drop. If this is not done you will have pipetted slightly less that the intended volume.
3. Volumetric pipettes, if clean and used properly, are precise to 0.01 mL. i.e. a 25 ml pipette delivers 25.00 mL, while a 20 mL pipette delivers 20.00 mL
4. How to rinse a pipette:

• Fill about half full with D.I. water.
• Rotate the pipette while holding it horizontally. Be sure that the water makes contact with all sides. Discard the water.
• Repeat the previous two steps with the liquid to be pipetted.
• Pipettes are clean if no liquid sticks to the sides after pipetting is completed. If sticking occurs the pipette must be returned for cleaning by the lab technician.

5. When finished, always rinse/wash the pipette with D.I. at least two to three times before returning it to the pipette container (contains a glass detergent) by the front desk—do NOT return a used/wet pipette to the container from which you got it.

Burettes

1. Burettes are designed to deliver any precisely measured volume of liquid up to the maximum of the buret capacity. Burettes have scale divisions of 0.1 mL. Estimates between scale divisions can be made. Therefore, all volumes should be recorded to the nearest 0.01 mL (e.g. 22.48 mL, 20.00 mL, 15.60 mL, etc.)

2. How to rinse a burette:

· Rinse the buret two to three times with about 15-10 rnL of D.I. water. Be sure that all inner sides make contact with the water. Run some of the water through the tip into a beaker to rinse the tip and stopcock. Discard the rinse water.

· Rinse the buret twice with about 5-10 mL of the solution to be titrated. Be sure that all inner sides make contact with this solution. Run some of the water through the tip into a beaker to rinse the tip and stopcock. Discard the rinse solution into the proper waste container.

· A buret is clean if no liquid sticks to the sides after releasing liquid. If sticking occurs the buret must be returned for cleaning by the lab technician.

3. How to fill a burette:

• Use a clean and dry funnel to fill a rinsed buret to about the 0.00 mL mark with the solution to be titrated.
• To expel air from the tip and stopcock, run some of the solution out into a small beaker. Tap the tip to dislodge air while letting the solution out. If the beaker is not clean and dry discard this solution in the proper waste container.
• Fill the burette somewhere between the 0.00 and 5.00 mL marks. Record this volume.
• Do not leave the funnel in the buret since liquid can drip down to give an inaccurate volume.
• Now the buret is ready for use.

4. When finished, always rinse the buret with Dl. at least two to three times before returning it.