CHEM 335 - Exam 1 Questions and Answers Latest Update Already Passed

CHEM 335 - Exam 1 Questions and Answers Latest Update Already Passed Pure Substance - Answers a homogenous sample consisting of molecules of having the same structure Effects of impurities - Answers - inhibit chemical reactions - catalyze undesirable side reactions - invalidate chemical test results The Recrystallization Process - Answers 1) Impure solid is dissolved in minimum amount of suitable solvent at its boiling point -- to form a saturated hot solution 2) When the hot saturated solution is cooled, the solid recrystallizes out of the solution 3) The impurity either remains in solution or undissolved throughout the entire process 4) The regenerated crystals are usually pure-- separated from solvent filtration Solubility of a chemical compound is enhanced through - Answers - mechanical action (swirling) - increasing amount of solvent - increasing temperature of solvent Most solids are soluble in - Answers hot over cold Recrystallization is based on - Answers temperature and amount of solubility characteristics Selecting an appropriate recrystallization solvent - Answers - minimal to no solubility of the compound at lower temps - complete solubility of the compound at its boiling point - completely dissolves all impurity at all temperatures OR does not dissolve impurity at all temperatures Solubility vs Temperature graph - Answers A good solvent has a steep slope and grams soluble increases as temperature increases For recrystallization experiments - Answers aim for complete dissolution at the solvents boiling point with minimum amount of solvent Color Impurities - Answers -removed using a decolorizing activated charcoal - activated charcoal is an adsorbent meaning it adsorbs chemical compounds present in solution - a small amount of charcoal is added to the hot solution - the process is repeated until the solution is clear - adding too much charcoal leads to lower recovery of the compound of interest Inducing Crystallization - Answers - Chill the purified solution (cooled filtrate) in cooling bath - Rub the tip of glass rod against the inside of the flask containing the purified solution (cooled filtrate) - Drop a pure seed crystal into the purified solution (cooled filtrate) - Reduce the volume of solvent by evaporation Causes of deviation from ideal recovery - Answers - incomplete recrystallization - loss during transfers - errors in quantifications Physical constant - Answers numerical values associated with measurable properties of chemical compounds Melting point - Answers -solid compounds at room temperatures -temperature at which the solid and liquid phase are in equilibrium at 1atm - Boiling Point - Answers liquid compounds at room temperature Refractive Index - Answers Liquid compounds at room temperature