![]() It helps to hold a white paper or card behind the cylinder at the meniscus. Make all measurements from the bottom of the meniscus. The concave surface of the liquid is called its meniscus. Graduated Cylinder Graduated cylinders are a simple way to measure liquid volumes. There is uncertainty associated with the volumes that volumetric flasks contain: The disposable pipets must be rinsed and placed in the broken glass container, not the trash. Fill to the graduation line dropwise using a disposable pipet (available in the front of the lab) and small pipet bulb. If it inadvertently is wetted, leave time for the liquid to drain off. Do not wet the ground glass joint at the top of the neck with the liquid. Using a funnel or pipet, fill the flask to just below the etched line with liquid. The uncertainty in the volume follows from the rules of error propagation i.e.,įigure 2 Make sure the flask is clean and thoroughly rinsed with a small volume to the liquid in use. The volume of solution delivered is the difference between these two readings. Then perform the titration and record the final reading. See the section on graduated cylinders below for a discussion of how to do this properly. Carefully read and record the level of solution in the buret before the titration. A typical reading should be recorded as 1.53 mL or 32.17 mL, for example, not as 1.5 mL or 32.2 mL. Always read your buret to this precision. You should be able to read between the marks to 0.01 mL. Burets are marked in 0.1 mL increments from 0 to 50 mL. two initial and final volume readings, which roughly doubles your error. Using over 50 mL of titrant to reach your endpoint requires you to refill your buret, which gives twice as many measurements i.e. If you use too small of a volume, your relative error in your measurement will be very large. When using a buret for a titration, you should be able to use volumes between 10 mL and 50 mL. You can dislodge bubbles by firmly flicking the tip or stopcock near the bubble. Make sure there are no air bubbles trapped in the tip or stopcock by opening the stopcock completely and letting some solution drain. Fill the buret to above the zero mark with the stopcock closed. Repeat the rinse procedure at least once more. ![]() Put the buret back in the ring stand and empty it into the waste beaker. Put a waste beaker under the tip of the buret just in case! Rinse the buret by adding a small amount of solution, remove the buret from the ring stand and rotate and tip it to wet the interior completely. To fill your buret, always place it with its ring stand on the floor, and fill it from the top with a funnel. Be sure the stopcock at the end is securely in place. See the above section on cleaning glassware. Before you use it, be sure it is thoroughly clean, drains freely, and does not leak around the stopcock. When you need one for an experiment, they will be available from the stockroom. Unlike the precise volumetric pipets (which only deliver one volume), burets can add any volume between zero and 50 mL. You can find clamps and ring stands in the back of the lab in the cupboards under the fume hoods.įigure 1 : Buret Burets allow for very precise volume measurements, far more precise than graduated cylinders. Buret Burets are long, thin calibrated columns of glass that are mounted vertically by a buret clamp to a ring stand. They are made of pyrex and may be heated. They are not to be used for volume measurements when accuracy is important. Beaker Beakers are roughly graduated and may be used for estimating the volume of a liquid. ![]() Usually you can get around the problem of wet volumetric glassware by rinsing it with 4 or 5 small aliquots of the solution to be measured so the solution replaces the water. Do not heat volumetric glassware (it will break if you do). If you must dry the inside of a flask, warm it gently over a Bunsen burner. Glass is easier to clean immediately after use than after it has dried dirty! You rarely need to dry glassware. Rinsing with many small portions is more effective (and cheaper) than with a few big ones. Finally, rinse 5 or 6 times with small amounts of distilled or deionized water. Be sure there are no exposed, sharp, metal points on the brush which can scratch the glass. Never put solid soap into glassware with narrow channels. To clean glassware, put detergent into a bucket and add hot water. If you see droplets on the glass, the glass is not clean. All volumetric glassware and flasks used for reactions should be thoroughly cleaned. A beaker used to hold ice for an ice bath doesn't need to be very clean. How To Use The Glassware Cleaning and Drying Glassware Determine how much time you spend cleaning a piece of glassware by thinking about its use.
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