Unformatted text preview: eneral Chemistry I and II Lab Manual because of mechanical difficulties this tends to produce. As you are filling the buret, at some
point, pause and look at the tip to be sure the liquid is not pouring out of the bottom. If it is, take
necessary action immediately to contain the reagent and clean up the spill. Fill the buret slightly
above the “zero” mark and return it to the buret clamp.
The buret is still not quite ready to use, because the tip of the buret is probably still filled
with air. If you try to measure the volume of liquid now, you will think you’ve added more
reagent than you actually have because this volume of air will show in the reading. Put either the
reagent beaker, or, better still, a waste beaker, under the buret tip and open the buret tip fully to
expel the air and fill the tip with reagent. Sometimes it helps to “flick” the buret tip to dis lodge
any stuck bubbles. When the tip is full of reagent (no air remaining), close the stopcock, and
check to be sure that the volume in the buret is now BELOW the zero mark. Do not waste time
trying to get the volume EXACTLY to zero; it does not matter what volume you actually have,
as long as you can read it (which is why it must be below zero).
Record the starting value; remember to estimate the volume to the nearest 0.01 mL (one
more significant digit than the graduations on the buret). Follow the titration procedure. If you
are right handed, the correct way to use the buret is as follows: use an Erlenmeyer flask (rather
than a beaker) for the titration. Once you have added the titrant (the chemical to be titrated) to
the flask, you can add additional distilled water as needed since this will not change the amount
of the chemical already in the flask. This is convenient for washing down droplets as they splash
onto the sides of the flask.
There is a proper, and an improper, way to add reagent from a buret. The proper way
feels a little bit cumbersome at first, but will give you better results. Begin by noting if you are
right or left handed; I will refer to them as your “dominant” and “secondary” hand. Position the
buret such that the stopcock control is on the same side as your dominant hand, and the scale is
facing you. The burets we use all have stopcocks that can be twisted around to accommodate
your dominant hand; be careful to do this before filling the buret, though, so the stopcock does
not fall out causing a chemical spill.
Now comes the part that throws most students. Even though the buret now looks like it is
set up to be controlled by your dominant hand, you will actually use your secondary hand to
handle the stopcock; your primary hand will be used to swirl the flask. Reach your secondary
hand around the barrel of the buret and the stopcock to control the flow from the buret, and use
your primary hand to swirl the flask. We do this so the tendency is to pull the stopcock in
tighter, rather than looser, so we don’t have to contend with a leak halfway through a titration.
This is not a two-person operation; the same individual who is cont...
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