Learning Objective: A volumetric pipet is a versatile and accurate fixed-volume measuring device. Here you will learn how to use a pipet.


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Volumetric glassware is used for precise and accurate volumes. The types of volumetric glassware you will use are volumetric flasks, volumetric pipets and burets. Flasks and pipets are in your locker while burets are located at your workbench or in one of the fume hoods.

To read the liquid level in all of these, find the bottom of the meniscus and read accurately from the graduations on the vessel. With volumetric flasks/pipets, align the bottom of the meniscus with the etched mark. When you do this, make certain that your eye is at the same level of the meniscus to avoid error due to parallax.

Be sure to wear gloves when rinsing the volumetric pipet with the solution.
   
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Volumetric pipets, like our 10 mL one, are used to transfer liquids or aqueous solutions. Always use a rubber bulb to fill pipets. It has a fixed silicone rubber adapter that can take pipets of different sizes. If you accidentally let a liquid or solution get into the bulb, empty the bulb at once and try to dry it with Kim wipes.

The first step is to rinse the pipet with deionized water. Pour deionized water into a beaker. Squeeze the end of the bulb with one hand and gently place the pipet inside it. Apply a gentle downward pressure on the bulb to make an airtight seal, and squeeze out some of the air in the bulb. Place the tip of the pipet into the beaker and ease up on the squeezing to draw water into the pipet until its approximately half full. Have your index finger or thumb ready to quickly place it on the opening of the pipet as soon as you remove the bulb from the pipet. This prevents the water from running out.

Turn the pipet horizontal and gently roll it so the water wets the entire inside surface. Once you're finished rinsing, drain the pipet in the sink.

   
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Before you can use the pipet to transfer your solution, you should rinse it with the solution. Pour the solution into a beaker. Attach the pipet to the bulb as you did in step 1. Place the tip of the pipet into the beaker and draw solution into the pipet by releasing pressure on the bulb. Once it's filled halfway, remove the bulb and quickly place your index finger on top. Turn the pipet horizontal and gently roll it to wet the inside surface. Discard the rinse solution into an appropriate waste container. After one rinsing (or two if desired), the pipet is ready for use.

   
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Make sure you have enough solution in your beaker and have the beaker to which you will transfer the solution handy. As you did in steps 1 and 2, attach the pipet to the bulb to draw the solution into the pipet. Avoid drawing the solution into the bulb. This time you need to draw enough solution so that the meniscus is above the etched mark. Remove the bulb and quickly place your index finger on top of the pipet.

Note that if you don't draw enough solution into the pipet, you may have to squeeze the bulb again at least once to draw in enough solution. Remember to use your finger to hold the solution in.

Remove the pipet from the solution, and wipe the pipet's tapered end with a Kim wipe. Then, holding the pipet in one hand and the waste container in the other, let the tapered end of the pipet touch the edge of the beaker. Bring the meniscus to your eye level and release your finger slightly from the top of the pipet so the meniscus drops slowly to the etched mark. When you think the bottom of the meniscus reaches the etched mark, reassert pressure on the top of the pipet. There should be exactly 10 mL of solution in the pipet.

With the pipet in one hand and the beaker into which you want to transfer the solution in the other, place the tip of the pipet on the edge of the beaker. Remove your index finger from the top of the pipet so the solution flows into the beaker.

   
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After draining the solution into the beaker, you will notice a small amount of liquid in the end of the pipet. Since this pipet is marked 'TD,' meaning 'To deliver,' the small amount of liquid remaining at the tip should not be blown out.


   
  note  

Graduated pipets are filled and drained just like volumetric pipets. Besides 'TD' pipets, there are also 'TC' pipets, meaning 'To contain.' The last drop in a TC pipet needs to be blown out. If you are not sure whether the last drop in a pipet should be blown out or not, look for a 'TD' or 'TC' label on the pipet, or check with your TA or instructor.




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