The Proper Use of a Pipette
 

Pipettes are stored on the same table as the Unknown solutions. They are stored upside down to facilitate draining.

Volumetric pipettes have only one mark. That's the line that marks the printed volume. Some pipettes have several marks and are called "graduated pipettes". They aren't as accurate as the volumetric types.

If you look close at the printed label, you will get more information. See below image for details.

10 mL pipettes
close up look at pipette label

You will now use the 10 mL pipette to add 10 mL of the unknown solution. Before you do that, you need to rinse out the pipette. See below for details.

Before you can rinse out the 10 mL pipette, you need to attach it to the pipette pump.

Unscrew the white collar a few revolutions. This widens the internal compression ring so the pipette can go in without too much force.

unscrew pipette pump end
Important: Grab near the upper end of the pipette. This will ensure that you don't bend the pipette and break it. Breaking it in your hand almost guarantees getting cut. Grab upper end of pipette
Important: As you insert the top end of the 10mL pipette into the collar of of the pipette pump, turn the pump to reduce the pressure needed to insert the pipette. Remember you are working with glass and you don't want it to break in your hand. Remember, do not bend the pipette. It needs to go straight in while you twist the pipette pump to make it go in easier. Turn pipette pump
After the pipette is inserted, twist the white collar and the green body in opposite directions to tighten it. This should create an airtight seal. You will know if there's an air leak when you draw liquid into the pipette. The liquid level will drop on its own if there's an air leak Tighten Collar
Push the plunger all the way down. This will allow the maximum volume of liquid to be drawn up into the pipette. Push plunger

If you have enough liquid, you should rinse out the 10 mL pipette using that liquid.

Set the tip into the beaker with the unknown liquid.

Turn the thumbwheel to draw up liquid (roll cursor over image to see use of thumbwheel).

Turn thumbwheel slowly to draw liquid up towards the top of the pipette (about 2 inches below the white collar of the pipette pump).

Again, if you have enough lquid, you can discard this liquid because it is just being used to rinse out the pipette. See the the below image on how to cause the liquid to drain out.

 

 

On the side of the pipette pump is the white fast-release lever. Press this when you want to let the liquid flow out of the pipette.

If the liquid you drew up first is only for rinsing out the pipette, push the fast-release lever to let the liquid drain into the waste beaker.

If you do not have enough liquid, then drain the pipette into the flask that you already weighed.

Release liquid by pushing button on pump

Draw up the liquid and bring the level about and inch or two above the 10 mL mark.

Raise the pipette so that its tip is above the surface of the unknown liquid. That's because when the tip is below the surface, the liquid's pressure pushes liquid upwards filling the pipette above the 10mL mark.

Push the release lever to bring the meniscus (bottom of curved surface) of the liquid to be level with the 10 mL mark. Your eyes need to be level with the mark. See below image for a better view.

set pipette into beaker
After you get the meniscus level with the 10 mL mark, you will move the pipette over to the Erlenmeyer flask that you just weighed. (This photo was taken from a high angle so the eyes look higher than they really were. They were level with the mensicus.) Eye level view

Press the white fast-release lever to allow the 10 mL to drain into the flask.

When the liquid stops draining, there will often be a drop of liquid clinging to the tip of the pipette. Simply touch it to the inside of the flask and it will come off.

 

Flask and pipette
Notice that there should be a little liquid left in the pipette. Remember, this particular pipette is the "TD" type meaning it will deliver 10 mL by draining out. If the pipette stated that it was a "TC" type, then that means "To Contain" in which case you blow out the last bit of liquid because it "contains" 10 mL. However, this TD pipette delivers 10 mL and its accuracy requires this amount of liquid remaining in the pipette. liquid still in pipette
Use a piece of a paper towel to grab the flask with the 10 mL of solution and carry it to the Mettler balance. Again, instead of a paper towel, you could use gloves. If you are skilled with tongs, then that is OK. Unfortunately, many students drop the flask when using tongs. Fill flask grabbed with paper towel