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Unformatted text preview: 37 Experiment 5 Identification of a Liquid by Physical Properties OBJECTIVE Expt 5 ID of Unknown.wpd Selected physical properties of an unknown liquid will be measured experimentally and compared with tabulated values of known liquids. DISCUSSION Any pure element or compound has a unique or intrinsic profile of chemical and physical properties. Therefore the properties of a sample of an unknown substance may be observed and compared with the properties of known substances tabulated in the chemical literature. If the properties of the unknown agree with the properties of a known, identification is assumed. Since many physical properties are recorded quantitatively (measured with numbers), it is often convenient to compare a set of physical properties of an unknown with sets of physical properties of knowns. Specifically in this exercise, the density, solubility, and boiling point of an assigned unknown liquid compound will be measured and compared to a given table of knowns. EXPERIMENTAL 1. Obtain an unknown sample for identification and immediately record the unknown number on the accompanying data sheet. 2. Density Another useful physical property is density, defined as mass per unit volume (D = M/V). Pure substances can often be identified by measuring their densities, since it is rare that any two substances have identical densities. The procedure that follows outlines a technique for determining the density of the liquid unknown. The approach requires the measuring of the mass and volume of a given unknown sample, and using these two values to calculate the density. Procedure: Carefully weigh a clean, dry 10-mL graduated cylinder to the nearest 0.001 g. Deliver a volume of unknown liquid to the cylinder to a point just short of the 10 mL mark and read the volume to an accuracy of one tenth (1/10) of the cylinder's smallest scale division. Weigh the filledvolume to an accuracy of one tenth (1/10) of the cylinder's smallest scale division....
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