First, the role
A burette is a gauge that accurately measures the volume of a standard solution during a titration operation. There are tick marks and values on the wall of the burette. The minimum scale is 0.1 ml. The “0” scale is on the top, and the values from top to bottom are from small to large.
Second, classification
According to the nature of the solution, there are two types: basic burette and acid burette.
The lower end of the basic burette is connected with a rubber tube, and a glass bead having a diameter slightly larger than the inner diameter of the rubber tube is placed in the tube to control the titration speed of the solution, and the lower end of the rubber tube is connected with a tip glass tube. An alkaline burette is used for the alkaline solution and the non-oxidizing solution.
The lower end of the acid burette has a glass piston switch that controls the titration speed. Acid burettes are used to hold acidic, neutral, and oxidizing solutions. They are not suitable for alkaline solutions because they can corrode glass and make the piston difficult to rotate.
Third, the operating procedures
Acid burette operation
1) Washing: When there is no obvious pollution of the burette, it can be washed directly with tap water. When there is oil stain, the washing powder solution can be used. When the inner wall of the burette is very dirty, it can be soaked for several minutes or several hours with the chromic acid washing solution. Finally, rinse thoroughly with tap water and then rinse with pure water three times.
2) Leak test: Close the cock, fill the burette with water, fix it on the titration tube holder, and place it for 5 minutes. Observe whether there is water seepage at the ends of the titration tube and the cock. The cock can be used without water seepage. If leaking, apply Vaseline: apply Vaseline to the cock (for sealing and lubrication). Pour off the water in the tube, lay it flat on the table, take out the cock, and blot the cock and the water in the sump with filter paper. Use a finger to rub a little Vaseline, apply a thin layer on both ends of the plug core (no Vaseline is placed in the small hole), then insert the cock into the plug groove and rotate it several times to make the oil film evenly transparent in the cock, and the cock is flexible.
3) Packing standard solution: The burette should be rinsed 3 times with standard solution (5-6ml), and the water film on the inner wall of the tube should be washed away to ensure the concentration of the standard solution is unchanged. The method is that the two-handed flat-end burette is slowly rotated to bring the standard solution into contact with the entire inner wall, and the solution flows out from the lower end of the burette.
4) Exhaust air bubbles: Check if there are air bubbles in the tip after loading the standard solution into the burette. If there are bubbles, it will affect the accurate measurement of the volume of the solution. To eliminate the air bubbles, hold the burette without a scale with your right hand and tilt it at an angle of about 30°. Open the cock with your left hand and let the solution quickly rush out to remove the air bubbles. After the bubbles are finished, add the standard solution to the 0 mark.
5) Titration operation: When performing the titration operation, the burette should be clamped on the titration tube holder. The left-hand controls the cock, the thumb is in front of the tube, the index finger and the middle finger are behind, the three fingers take the stalk handle slightly, the fingers are slightly bent, and the cock is buckled inward to avoid the force that pulls the cock out. Rotate the cock inward to allow the solution to drip out. The burette should be inserted into the conical bottle mouth 1-2cm, and the bottle should be held in the right to make the solution in the bottle rotate continuously clockwise.
Basic burette
1) Washing
2) Test leak: test leak. The alkaline burette was filled with water and then placed on the titration tube holder for 5 minutes. If there is water leakage, replace the rubber tube or the glass beads in the tube until there is no water leakage and the droplets can be flexibly controlled.
3) Packing standard solution
Air bubbles: The method is: bend the rubber tube upwards, tilt the outlet, squeeze the glass beads, and quickly eject the solution from the tip, and the bubbles can be drained.
4) Titration operation: When performing the titration operation, use the thumb and forefinger of the left hand to pinch the outside of the rubber tube in the upper part of the middle part of the glass bead, and squeeze the rubber tube in the direction of the palm to form a gap between the glass beads and the solution. Can flow out.
Fourth, matters needing attention
1) The burette should be washed before use and after use. The standard for burette cleaning is that the inner wall of the glass tube does not hang water droplets.
2) The burette must be fixed to the titration tube holder for use. When reading the burette reading, make the burette vertical and the line of sight should be on a level with the lowest point below the meniscus. Read to the second decimal place (0.01ml)
3) During the titration, the eye should look at the change in color in the conical flask, but not the burette.
4) Dropping speed: first drop and then drop slowly (cannot be connected to the water column). When approaching the endpoint, it should be shaken one by one.
5) End point: The last drop just makes a significant change in the color of the indicator and does not restore the original color within 0.5 min. The final volume is read and recorded.
Should you have any inquiries, do not hesitate to get in touch with WUBOLAB, the laboratory glassware manufacturer.
