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Unformatted text preview: luid still is too rapid, CAREFULLY put
the tip of the pipette direction onto the bottom of the container with the fluid.)
Once the fluid is at the correct level, lift the pipette out of the fluid, and touch the tip to
the side of the container to get any excess drops off. Put the pipette over the container you want
the liquid in, and take your finger off of the top of the pipette. Holding the pipette vertically,
allow the fluid to flow out on its own WITHOUT trying to force the liquid out. Once the flow
stops, touch the tip of the pipette to the side of the container to get any last drops off and remove
the pipette. You will notice that a small amount of liquid remains in the pipette; do NOT try to
“blow” this last drop out. The pipette is calibrated to keep this amount of liquid in the pipette, so
if you blow this last bit out, you have ruined the calibration and do not know precisely how much
liquid you have.
If necessary, wash the reagent down the side of the container with a distilled water bottle.
The volumetric flask is a piece of volumetric glassware (calibrated to four significant
figures) designed to contain the volume on the flask. Notice on the neck that there is a single
calibration mark; when the flask is filled to this mark (with the bottom of the meniscus), it
contains the volume indicated.
There are a couple of tricks that are necessary
to make it easier to work with a volumetric flask.
First, make sure you have the correct size lid. Plastic
tops are probably better than ground glass for general
purpose since ground glass tops can easily dry out
and get stuck or damaged. The T/S number on the
flask should be identical to the one on the stopper, so
if the flask reads T/S 19, get a T/S 19 stopper.
If you are dissolving materials in the flask,
once you have placed in your reagent, do not fill the
flask to the graduation mark initially. Instead, fill the
bulb about half full; this will allow you to swirl more vigorously to get the solid to dissolve. If
you want to shake the flask, put the stopper on it first. If the solid does not dissolve immediately,
add a little more water and continue. Once the solid has dissolved completely, fill the flask to
the graduation mark.
Notice that if you stop here, the solution in the neck is not mixed thoroughly with the
solution in the bulb. The next step is to put the stopper on it, and hold the flask such that your
Dakota State University Page 39 of 232 Basic Laboratory Procedures General Chemistry I and II Lab Manual palm is holding the stopper relatively firmly on the flask. Invert the flask, and swirl it relatively
vigorously. Return the flask to it’s upright position, allow the fluid to flow out of the neck of the
flask, and repeat the procedure. Typically you will want to invert and swirl a minimum of three
Finally, avoid handling the volumetric flask by the bulb at the bottom. It is best to handle
it with the neck above the graduation mark for the same reason that you...
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