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f)
Remove the bulb quickly and cover the top of the pipet with the index finger of your dominant
hand.
g)
Remove the pipet from the solution and wipe the outside of the pipet with a paper towel.
h)
Hold the pipet vertically over a waste beaker and allow the pipet to drain to the zero mark by
gradually releasing the pressure of your finger on the top of the pipet and gently rotating the pipet
at the top of the solution container. Continue to keep your finger resting lightly on the top of the
pipet. When the meniscus reaches the mark, stop the flow of liquid from the pipet by firmly
forming a seal on the top of the pipet with your index finger.
i)
Touch the tip of the pipet to the dry wall of the waste vessel to remove any excess drops and then
transfer the pipet quickly to the erlenmyer flask which is to receive the sample.
j)
With the pipet held vertically, allow the solution to drain freely with the tip of the pipet touching the
way of the flask. .
k)
After free flow stops, the tip is held in contact with the inner wall for a full 10 seconds (draining
time). Do not blow or shake out the small amount remaining in the tip, as the pipet is calibrated to
deliver a specific volume with a small amount remaining in the tip.
m)
Using your wash bottle, rinse down the wall of the flask to ensure that any drops of the sample
adhering to the inner wall are mixed with the rest of the sample in the flask.
l)
Never use your mouth to draw liquid into a pipet!
D.
Heating Samples
1.
Hot Plates
Hot plates will generally be used as the heat source in this laboratory. A setting of 3-4 on most
hot plates is sufficient to heat the solution quickly. NEVER turn the hot plate to “high” because
of the danger of burning the sample and yourself.
2.
Bunsen Burners
On occasion you will be required to use the gas flame from a Bunsen burner to heat a sample
intensely. Because of the inherent dangers of using an open flame, it is very important that you
understand how to use a Bunsen burner properly.
The first illustration shows the Bunsen burner, the second shows the structure of a good flame.
