A burette is used to deliver solution in precisely measured, variable volumes. Burettes are
used primarily for titration, to deliver one reactant until the precise end point of the
reaction is reached. To fill a burette, close the stopcock at the bottom and use a funnel. You
may need to lift up on the funnel slightly, to allow the solution to flow in freely.
You can also fill a burette using a disposable transfer pipette. This works better than a
funnel for the small, 10 mL burettes. Be sure the transfer pipette is dry or conditioned with
the titrant, so the concentration of solution will not be changed.
Before titrating, condition the burette with titrant solution and check that the burette is
flowing freely. To condition a piece of glassware, rinse it so that all surfaces are coated
with solution, then drain. Conditioning two or three times will insure that a stray drop of
water does not change the concentration of titrant.
Rinse the tip of the burette with water from a wash bottle and dry it carefully. After a
minute, check for solution on the tip to see if your burette is leaking. The tip should be
clean and dry before you take an initial volume reading.
When your burette is conditioned and filled, with no air bubbles or leaks, take an initial
volume reading. A burette-reading card with a black rectangle can help you to take a more
accurate reading. Read the bottom of the meniscus. Be sure your eye is at the level of
meniscus, not above or below. Reading from an angle, rather than straight on, results in a
parallax error.
Deliver solution to the titration flask by turning the stopcock. The solution should be
delivered quickly until a couple of mL from the endpoint. The endpoint should be approached
slowly, a drop at a time. Use a wash bottle to rinse the tip of the burette and the sides of
the flask. Your TA can show you how to deliver a partial drop of solution, when near the
endpoint.
sharon kalunda answered the question on
April 12, 2019 at 05:54