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e)
End point - There is a local transient
indicator color change where a drop from the buret
enters the solution. As the trail
of color persists longer and longer, make additions smaller
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.
