Calibrating a Pipet
A small plastic or glass dropper pipet can be calibrated by counting the number of
drops of water it takes to make a certain volume.
1. Fill the pipet.
2. Counting each drop, squeeze the pipet gently to release water drop by drop into a dry
10 mL graduated cylinder.
3. Stop when you have 2 or more mL of water in the graduated cylinder.
4. Read the volume of water in the graduated cylinder, at the bottom of the meniscus.
5. Calculate the number of drops it takes per mL. Divide the total counted drops by
the volume of water.
6. To measure a mL (or fraction of a mL) count out the appropriate number of drops.
There are two useful relationships you can use to measure volume with your pipet.
| The volume of a single drop |
|
The number of drops per mL |
| V = |
Total number of drops
Measured volume (mL) |
|
|
| Drops per mL = |
Measured volume (mL)
Total number of drops |
|
