What is the Burette?
is an instrument in chemical experiments and one of the basic instruments for volumetric analysis. A precision glass measuring device in the shape of an elongated tube.
A volumetric burette
. The temperature and level are displayed at the top.
is a measuring device, which holds the titrant solution during the titration operation and releases a certain amount of solution to the titration end point. The tube is engraved with a precise scale, which can accurately read the volume of the solution released.Burettes
are generally divided into two categories according to whether the piston is used or not: burettes
with plugs and burettes
without plugs, and they are also called acid-type and basic-type burettes
because of the nature of the liquid they hold respectively.
needs to be cleaned before use. Generally, use distilled water (or deionized water) to wash 2 to 3 times each; if there is oil stain, first wash with lotion or detergent. Since the burette
is a measuring tool and has a concentration requirement, it needs to be rinsed 2-3 times with the solution to be loaded. For the sake of economy, cleaning and rinsing adhere to the principle of small amount and many times.
After rinsing, the solution should be loaded and drained to remove air bubbles from the lower part of the tube. The stoppered burette
can open the piston and discharge the liquid. For burettes
without stoppers, bend the tip upward and squeeze the glass beads in all directions to push the liquid out of the tip and dislodge air bubbles.
The liquid forms a meniscus in the tube. When reading, look up and read, in principle, read the number of milliliters corresponding to the bottom of the liquid level. Looking down or looking up introduces parallax. Because the number of readings is required before and after the titration, it is necessary to discharge the liquid to the scaled part before the titration, usually to the "0" scale or an integer scale.
The method of discharging is that the stoppered burette
can open the piston, and the unplugged burette
squeezes the glass beads to create a gap between the glass beads and the rubber tube. In principle, the graduated side of the burette
should face the operator, the piston should be controlled with the left hand, and the titrant should be dispensed drop by drop. However, if the approximate range of the end point is known during titration, the liquid can be quickly discharged to about 95% of the end point. Considering that rapid liquid discharge may cause the liquid to hang on the wall and cause inaccurate readings, wait for a while after liquid discharge to allow the wall-mounted liquid to flow down.
In order to precisely control the amount of titrant, one method that is often used is to dispense only "half a drop". "Half drop", that is, close the piston when a drop of solution has not completely dripped out, and then use the conical bottle mouth below to push the liquid down. The volume of a "half drop" of a constant burette is about 0.02 mL.