Principles of Chemistry Lab
CHEM 1211 L Principles of Chemistry Lab
16 February 2004
Lab Report 1
Introduction
The purpose of this project is to identify an unknown organic acid (X) by conducting various experiments to determine the acid’s unique properties. By determining selected constant properties of the unknown and then comparing these properties to the constant properties of known substances, it is possible to identify an unknown substance. The properties used to identify the unknown must be intensive, or independent of amount. Both chemical properties and physical properties are intensive properties used in determining the identity of an unknown (Maserton, p. 15).
Because even small amounts of impurities systematically affect observed chemical reactions, the first step to determine the identity of an unknown is to purify the substance. One technique often used to purify solids is recrystallization from a selected solvent. Because of the variable solubility of different compounds in various solvents and at various temperatures, it is possible to remove impurities by dissolving the unknown and then immediately cooling the solvent. The unknown recrystallizes, but the impurities remain dissolved in the solvent. It is then a relatively simple matter to filter the pure crystals out of the impure solvent (Lab Manual, p. 32). Once the unknown has been purified, it is possible to begin determining its constant properties. One specific physical property that is helpful in identifying an unknown is the substance’s melting point (Lab Manual, p. 36). Equivalent weight, the weight in grams of the acid that contains exactly one mole acidic hydrogens, is also useful when identifying an unknown acid. Equivalent weight is determined by the pairing the unknown’s acidic hydrogens (H+) with known quantities of hydroxyl ions (OH-) through the process of titration. Before beginning a titration of the unknown acid, several practice titrations of HCl (hydrochloric acid) with a known
16 February 2004
Lab Report 1
Introduction
The purpose of this project is to identify an unknown organic acid (X) by conducting various experiments to determine the acid’s unique properties. By determining selected constant properties of the unknown and then comparing these properties to the constant properties of known substances, it is possible to identify an unknown substance. The properties used to identify the unknown must be intensive, or independent of amount. Both chemical properties and physical properties are intensive properties used in determining the identity of an unknown (Maserton, p. 15).
Because even small amounts of impurities systematically affect observed chemical reactions, the first step to determine the identity of an unknown is to purify the substance. One technique often used to purify solids is recrystallization from a selected solvent. Because of the variable solubility of different compounds in various solvents and at various temperatures, it is possible to remove impurities by dissolving the unknown and then immediately cooling the solvent. The unknown recrystallizes, but the impurities remain dissolved in the solvent. It is then a relatively simple matter to filter the pure crystals out of the impure solvent (Lab Manual, p. 32). Once the unknown has been purified, it is possible to begin determining its constant properties. One specific physical property that is helpful in identifying an unknown is the substance’s melting point (Lab Manual, p. 36). Equivalent weight, the weight in grams of the acid that contains exactly one mole acidic hydrogens, is also useful when identifying an unknown acid. Equivalent weight is determined by the pairing the unknown’s acidic hydrogens (H+) with known quantities of hydroxyl ions (OH-) through the process of titration. Before beginning a titration of the unknown acid, several practice titrations of HCl (hydrochloric acid) with a known
Cited: Maserton, William L. and Cecile N. Hurley. Chemistry: Principles and Reactions, 5th ed. Thomson Learning, Inc., Toronto, 2004. The Identification of an Organic Acid, 3rd ed. Georgia State University, Atlanta, 1992.