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Unformatted text preview: 1 Liquid Density Measurements and Sugar Concentration of Coke Learning the techniques of common laboratory measurements is a principle goal of the laboratory experience in Chem 123. When you have completed this course you will have competencies in a number of laboratory techniques. The lab today will introduce you to the techniques of mass and volume measurement and to record experimental results. The density of a compound, often in units of g/mL, is an important property of a substance. The density, ratio of mass to volume, is an intensive property, which means that the quantity of material does not affect the density. The density of gold (19 g/mL) was used to distinguish pure gold from fake gold that was often of a lower density. Solution density is also used to determine the alcohol content of solutions, this technique is of major importance in the beer and wine industry. Overview: The density of Coke will be measured using two different techniques for the measurement of volume. A calibration plot of sugar concentration vs solution density will be constructed in order to determine the approximate sugar content of Coke. By measuring a sample’s mass and volume, the density can be determined. During this experiment the volume of the sample will be measured in two different ways and the mass will be obtained from a digital balance. Mass Measurements on the Wofford Digital Balances: Never add a chemical to a container on a balance. In this course you will mass a sample using the “mass-by-difference” technique. To do this you will make two mass measurements and the difference in these masses is the mass of your sample. Two examples of this technique are given below. The most difficult aspect of these two massing techniques is estimating the amount of sample to be transferred. Usually you will be weighing gram quantities. These are in the ballpark of a half-teaspoon. By the end of the semester will be good at estimating these quantities. Often you do not need exactly 0.500 g of material. You can use 0.626 g of CaCO 3 if the procedure calls for half of a gram. You, of course, record that you have obtained 0.626 g of CaCO 3 . This is sometimes called “weigh exactly about”. If you are doing a laboratory synthesis that requires an exact amount of a substance, use the second example of mass determination, in which case you can add and subtract from the sample dish several times, but never add or remove chemicals while the dish is on the balance. 23.455 g 22.878 g Remove the approximate amount of reagent to be used. Obtain the mass of the reagent container....
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- Spring '09