Identification of substance by physical properties
Prepared for: Laura, Mudaugh
Prepared by: Mohamed, Seaid
February 14, 2013
The purpose of this lab was to identifying unknown substances by knowing their physical properties as density, melting and boiling point, and their solubility in specific solvent. The unknown solid was determined and found to be a solid Nephthol. Also, the unknown liquid was determined and found to be Cyclohexane.
Properties are those characteristic of substance that enable one to identify it and to distinguish it from other substance. To identify an unknown substance, one must examine its physical properties. Physical properties are those properties that can be observed without altering the composition of substance. Physical properties, for example as solubility, boiling point, melting point, color, size, shape, or texture. The solubility of a substance in a solvent is the maximum weight of that substance to dissolve in the given volume of a solvent. Density is the ratio of the mass of an object compare to its volume. The melting point is the equilibrium temperature when approached from the solid phase- that is, when liquid begins to appear in the solid. And the boiling point is the point that when a liquid is heated and started to make a bubbles of vapour form in it, rise rapidly to the surface, and burst. However, in this experiment, an unknown solid and unknown liquid had been given to identify them by knowing their solubility, boiling point, melting point, and density.
Step A the solubility of nephthalene has been determined by using three kind of solvents. A small amount of nephthalene had been added to 3 ml of water, cylohexane, and ethyl alcohol separately to determine the solubility of the nephthalene in each solvent and the observations had been recorded in the lab notebook. Then 3 ml of the same solvents had been added to three clean test tube seperatly and then 4 to 5 drops of toluene solution had been added to each test tube to determine the solubility of toluene in each solvent. In the same way, a small amount of the unknown solid (c) had been added seperatly to 3 ml of water, cyclohexane, and ethyl alcohol to each one it to determine the solubility of that unknown solid in each of the solvent. Then to determine the solubility of the unknown liquid (A), to each of the three solvents water, cyclohexane, and ethyl alcohol a 4 to 5 drops of that unknown liquid had been added seperatly to each solvent to determine the solubility to that unknown liquid. However, the density of the unknown solid (c) had been calculated by measuring the volume of half full of a graduated cylinder t at filled up with water and then 1.5 g of that unknown solid had been poured into the graduated cylinder. Then the density of the unknown solid had been calculated and recorded in the lab notebook. In the same way, the density of the unknown liquid had been calculated by weighting an empty 50 ml Erlenmeyer flask to nearest 0.0001g. Then 10 ml of the unknown liquid had been added to the flask and the final volume had been recorded. Then the density of the unknown liquid had been calculated and recorded in the lab notebook. Yet, a 5 mm of the unknown solid had added to a capillary tube and a small rubber band and heated until it melted completely. The beginning of the melting point and the point that the unknown solid melted completely had been recorded in the lab notebook. In the same way, a 3 ml of the unknown liquid had been heated inside a beaker full of water and the boiling point to the unknown solution had been measured and recorded in the lab notebook. Finally, the physical properties to the unknown solid and liquid had been compared with the physical properties of the pure substance and the identification to the unknown solid and the unknown substance had been recorded in the lab note book.
Result and Data: In the first part