Below are instructions for proper pipetting/dilution procedure. Please ask your instructor if you have any questions about the procedure below and the purpose of each step in the procedure.
Wear safety glasses.
Never dip a pipette directly into a reagent bottle. Place your reagent in a small beaker and pipette from the beaker. You will want 10-15mL more liquid than you need, but don't be wasteful.
Rinse your volumetric pipette with your solute-containing solution:
Draw solute-containing solution into the pipette until it starts to fill the bulb in the center of the pipette.
Rinse your pipette by rotating it on its side, being sure to rinse above the fill line.
Let rinse solution drain into a waste beaker.
It is good practice to rinse your pipette three times.
Filling the volumetric pipette:
Draw solute-containing solution into pipette, until the meniscus is a few cm above line.
Drain the pipette until the bottom of the meniscus is at the fill line, while maintaining contact between the tip of the pipette and the side of the beaker. Ensure that your eyes are level with the fill line. When level, you should not see the back of the fill line on the pipet since it will be blocked out be the front of the fill line on the pipette. Note: touching the tip of the pipet on the bottom of the beaker will cause the solution to drain slower. If you drain below the fill line, refill and try again.
Draining the pipette:
Holding the pipette vertically, touch tip of pipette to inside of the volumetric flask, which should be held at an angle.
Let liquid drain by gravity.
Some solution will remain in the tip of the pipette. This is intentional (it is accounted for when the pipettes are calibrated).
Allow the remaining solution to remain in the tip of the pipette. This amount has been accounted for in the volume of the pipette.
Filling the volumetric flask:
Obtain a beaker of deionized water.
If you like, you may pour deionized water into the flask until the liquid level is a few cm below the fill line. Be careful not to over-fill!
With the volumetric flask on the benchtop, move your eye to be level with the fill line...as you did with the pipette.
Use a disposable pipette to add deionized water until the bottom of the meniscus is at the fill line. Be careful not to over-fill!
Put stopper on flask and mix by inverting 4-5 times. Make sure that the air leaves the neck of the flask when inverting.
Please see the following YouTube videos for how to use a volumetric pipet and a volumetric flask: