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and smaller. Near the endpoint, you should add 1 drop of titrant (0.05 mL) at a time. The
tip of the buret should be touched to the inner wall of the flask to transfer any hanging partial
drop. Wash down the sides of the flask with a small amount of water from a wash bottle.
The titration is complete at the first indication of a permanent color change.
2.
Use of a Volumetric Flask
The volumetric flask enables you to prepare solutions of a specified concentration. Dissolve a
known quantity of soluble solid in a beaker with a minimum amount of water. Set up a clean
funnel in an iron ring that is supported by a retort stand and adjust the tip of the funnel so that it
fits into a volumetric flask. Pour the concentrated solution down a stirring rod and into the
flask. Rinse the beaker, stirring rod, and funnel thoroughly with water sprayed from a wash
bottle so that all the washings go into the flask. Repeat these rinsings 3 times to ensure all of
the solute has been transferred to the volumetric flask. Remove the funnel when the level of
the water is just below the neck of the flask. Stopper the flask and swirl the flask to dissolve
the solid but be careful not to allow solutions to touch the stopper or rise above the ground glass
volume mark on the neck of the flask. Remove the stopper and add water drop-wise until the
bottom of the meniscus is level with the volume mark on the neck of the flask. Stopper the
flask again and with the stopper held firmly in place, repeatedly invert the flask for one to two
minutes to thoroughly mix the solution.
3.
Use of a Pipet
a)
Clean and wash the pipet with water.
b)
Rinse the pipet with 2-5 mL of the solution to be pipetted and discard the washings.
c)
Repeat step 2.
d)
Fit a squeeze bulb on the top of the pipet. The squeeze bulb should rest lightly on the top
of the pipet and should not be forced onto it.
e)
With the tip of the pipet out of the solution, hold the pipet with your dominant hand and the
squeeze bulb firmly with your other hand to expel all of the air in the bulb. Put the tip of the
pipet into the solution and slowly release pressure on the squeeze bulb to allow the liquid to
rise in the pipet past the zero mark and nearly to the top of the pipet. Then, maintain a
steady pressure on the squeeze bulb so that liquid stops rising before it is drawn into the
bulb.
