While the described demonstration may merely serve to illustrate density to younger students, a more quantitative approach could be used with older students when introducing molarity and dilution calculations.A larger (1 liter) graduated cylinder may be used for an even more impressive display, but the quantities of solutions will need to be doubled.Commercial orange food coloring may look too yellow or red, so the orange color is best prepared by mixing a drop or two of yellow and red.Note that the slower the filling rate, the better the layer separation will be. Teachers should test the filling process with water before class so the cylinder will fill at a rate of about 75 -100 cm 3 per minute. To speed up the process and still retain a good separation of solution layers, the pipet should be cut about 2-3 cm from the tip by scoring with a triangular file and snapping off the lower piece of the pipet. While Pasteur pipets taper to a narrow opening that will slow down the rate of graduated cylinder filling, this may be too slow to demonstrate during a class.When breaking the pipet tip, hold it between a cloth or wear thick gloves.
Safety Notes: Sugar solutions may be discarded down a sink. If this is done carefully, there will be no mixing of the solutions when the funnel stem is withdrawn. Slowly lift the funnel from the cylinder. To remove the thistle funnel, first place a stopper tightly in the funnel to prevent any solution remaining in the stem from draining out when the funnel is removed. The total time to fill the cylinder will be 5-10 min, depending on the width of the pipet tip. Continue with successive solutions until the purple solution has drained from the funnel (500 cm 3 graduated cylinders actually hold about 600 cm 3). As it empties into the graduated cylinder, top up the reservoir. Quickly add the next (orange) solution just before the funnel reservoir empties to avoid air bubbles forming in the funnel stem. Begin by pouring the red (least concentrated) solution into the funnel reservoir. Place the six colored solutions next to the 500 cm 3 graduated cylinder containing the adapted thistle funnel. Students can use data to practice molarity and dilution calculations in the classroom. Video 1: Density Column, Online Chemistry YouTube Channel (accessed 3/22/21)ĭensities of each solution were measured which students may calculate using data provided in table 1 below. To narrow the funnel’s stem opening, a Pasteur pipet is attached via a short piece of rubber tubing producing a near perfect separation of colored layers. The sugar solutions are introduced sequentially into the cylinder via the funnel from the least to the greatest density. However, the funnel’s stem is generally too wide leading to rapid drainage and the partial mixing of layers as the cylinder fills. This article also describes a convenient procedure for filling a sugar density column using a slightly modified thistle funnel to fill a large graduated cylinder in reverse density order to produce remarkably distinct layers for an attractive classroom display of density (see Video 1). 7 The procedure described here uses accurate concentrations. While solutions are usually prepared individually, in kitchen cups or glasses, with little graduated accuracy using tablespoon quantities of sugar, 4-6 more careful preparations have been reported. 1-3 Colored sugar solutions of varying concentrations can similarly be layered to illustrate density and generally require the lower density solutions to be carefully poured onto the higher density solutions to minimize mixing the miscible layers 4-7 although this is generally unavoidable. Demonstrating the densities of various liquids (oils, alcohol, detergent, syrup, etc.) in a tall glass container is a popular at-home science activity described on many websites.
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