Cleaning the Buret
In order for your buret to perform optimally, it must be properly cleaned. To clean the buret, use the following procedure:
- Rinse with distilled water:
With the stopcock closed, add some distilled water to the buret. Tip and roll the buret, allowing the water to have contact with all of the inside surfaces. Open the stopcock and allow the water to drain. If the water drains without leaving any droplets on the side, repeat the rinse twice more then move to step two. If droplets remain on the inside surface, wash the buret with detergent solution, rinse several times with tap water, then rinse three times with distilled water.
- Rinse with solution:
After draining the final distilled water rinse, close the stopcock and add about 5 mL of the solution to be dispensed from the buret. Again, roll and tip the buret so the solution has contact with all the inside surfaces. Open the stopcock and allow the solution to drain. Repeat this twice more. Discard the solution used in the rinses.
- After you are finished with the buret in your experiment, rinse it by filling it with distilled water and allowing it to drain.
Once the buret is clean, clamp it to a stand using a buret clamp. Always make sure the burette is clamped in a perfectly vertical position before taking any readings.
When adding solutions to the buret, make sure the stopcock is closed (horizontal position). Unclamp the buret and tilt it slightly while pouring the solution slowly down the inside surface. This will prevent the formation of air bubbles.
- Get the appropriate amount of solution in a clean, dry beaker.
- Pour a few milliliters of solution into the buret. Open the stopcock all the way in order to force all the air out of the stopcock and tip. Close the stopcock before the solution drains below the stopcock. If the tip still contains air, add a few more milliliters of solution and repeat the process. Repeat this until you are convinced no more air is left in the stopcock or tip. Discard the solution that you have run through the buret.
- Using the procedure described above for adding solutions to the buret, fill it to a level just above 0.00 mL. Drain the buret to just under 0.00 mL. This will properly form the meniscus. DO NOT ATTEMPT TO ADJUST THE MENISCUS TO EXACTLY 0.00 mL. THIS IS AN INCREDIBLE WASTE OF TIME.
- Touch the tip of the buret to the inside wall of a beaker in order to remove any drops on the tip. Do not wipe the tip. Wait a few seconds for the solution to drain to the top of the fluid level, then record the initial buret reading in your notebook.
- Loosely cover the top of the buret with a cocked, small beaker or a loosely fitting piece of aluminum foil. This will keep dust out of the buret.
- In order to make the meniscus easier to see, place a white card with a black mark on it behind the buret. Align the black mark so that it is just under the meniscus.
- Get your eye level with the bottom of the meniscus. Looking up or down on the meniscus will cause a parallax error.
- Read the buret to the nearest 0.01 mL. The marks occur every 0.1 mL, so the last number will have to be an estimate. With practice, you should be able to do this quite accurately.
Proper buret technique is an important laboratory skill that may take some practice to develop. Although is may seem initially awkward, a right handed person should operate the buret with the left hand, and a left handed person should operate the buret with the right. This leaves your more coordinated hand to swirl the reaction flask if needed.
- Before delivering any solution, record the initial buret reading in your notebook.
- Open the stopcock by twisting it 90 degrees into the vertical position and allow the solution to drain. As you near the desired volume, slow the flow by turning the stopcock back toward the closed position. You should be able to control the buret to deliver one drop at a time. When the desired volume has been delivered, close the stopcock.
- Wait a couple of seconds, then record the final buret reading.
- Calculate the volume delivered by subtracting the initial reading from the final reading:
initial reading - final reading
When delivering solutions, you must not allow the solution to drain below the bottom of the calibration range. If this is about to occur, close the stopcock and take a final reading. Refill the buret, get an initial reading, and continue delivering solution. The total volume delivered is the sum of the volume delivered the first time and the volume delivered the second time.
Laboratory Information
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