Unformatted text preview: rolling the flask also controls
the buret, and reads the volumes on the buret.
Once the endpoint is reached, read the final volume in the buret. The volume added to
the flask is this volume minus the initial volume. You need not refill the buret after each run; if
you still have enough liquid in the buret for a second run (which should have the same volume as
the first run), you can just use the liquid that is already in the buret. Only refill the buret if
necessary (and remember; do NOT refill the buret in the buret clamp!). If you underestimate the
volume in the buret, do not try to “save” the run by letting the liquid run below 50 mL in the
buret, or by adding liquid mid-titration. These are designed to be exceptionally high precision
Dakota State University Page 45 of 232 Basic Laboratory Procedures General Chemistry I and II Lab Manual experiments; either of these techniques will introduce undue error into your calculations. Just
refill the buret, and do another run.
Cleaning laboratory Equipment:
Finally, we come to the general process of cleaning laboratory equipment. This is
critical; contaminants can have a profound influence on an experiment, and since equipment is
shared, you will want to be sure the glassware is clean from the other groups. Heck, you don’t
know what they did! So how does one go about cleaning laboratory glassware? Easy; you make
your lab partner do it.
But what if YOU are the lab partner? OK, well, it’s really not that bad. The first thing
you will want to recognize, however, is the simple fact that glassware is easiest to clean before
the gunk has the opportunity to dry into it. However, the same basic rules apply even if it is old.
Begin by rinsing very well with tap water (surprised?). You will find an assortment of brushes
near each sink; rinse out as much of the bulk of the contaminants as possible. Then, still using
tap water, add Alconox. Alconox is a white cleaning agent at each sink; it is a detergent made
BY chemists FOR chemists. This is good stuff; it’s like Lava soap with an attitude. Use the
brush to clean the glassware thoroughly; if you are cleaning something that cannot be cleaned
with a brush (like a pipette); dissolve a little Alconox in a beaker of water and run it through as
best you can.
After cleaning with Alconox, rinse the glassware VERY THOROUGHLY with TAP
water to get rid of all of the excess soap. If you are not happy with how clean it is, repeat the
step with Alconox. Finally, rinse it THREE TIMES with SMALL amounts of distilled water (in
the large carboys near each sink). Do NOT allow the distilled water to run the entire time during
the rinsing process; open the spicket just long enough to allow a small volume (maybe 5 mL)
out, and close it again. Rinse thoroughly and repeat two more times. It does take time to make
distilled water, so if we run out during a lab, there is nothing I can do about it. If you are
working with something like a pipette, run distilled water through it using a wash bottle.
If the glassware is clean, the water shoul...
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