Key Practice CHM 152 LL Exam questions 1. The following experiment was conducted to find the enthalpy of vaporization of a liquid, using the Clausius-Clapeyron equation, the result in the table below was obtained. Temperature (°C) Pressure (Torr) 20.2 16.5 99.8 700 Calculate the heat of vaporization of the liquid. (R = 8.314 J/mol. K). Answer: T1 = 20.2 + 237.15 = 293.35 T2 = 99.8 + 273.15 = 372.95 -3.748 = -3.748 = = 42686.13 = 2. Calculate concentration for a Cr3+solution with absorbance of 0.17, a molar absorptivity of 670 L/mol.cm, in a cuvette with path length of 1.2 cm. Answer: abs = εlc ε = molar absorptivity l = path length c = concentration 0.17 = (670 L/mol.cm) (1.2 cm) x c = c 0.000211 mol/L = c 3. Name two types of chromatographic techniques, their driving force, stationary phase, mobile phase and their uses. Answer: 1) Paper Chromatography. Driving force is capillary action Stationary phase is paper Mobile phase is liquid aqueous or organic solutions of dissolved compounds. Used to resolve mixture of pigments 2) High-performance/ pressure liquid chromatography (HPLC) Driving force is pressure forcing liquid through the column Stationary phase is column silica gel, alumina, sand, ion-exchange resin, etc. Mobile phase is liquid aqueous or organic solutions of dissolved compounds.
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Used to resolve mixture of substances 4. What is the difference between a homogenous and a heterogeneous mixture? Answer -Homogenous mixture, is when the components of the mixture cannot be distinguished by the observation method. -Heterogeneous mixture, is when the components of the mixture can be distinguished by the observation method. 5. Outline the basic principle that controls the use of any chromatographic technique as a means to separate mixtures. (e.g. Types of phases and Rf value). Answer A solvent (mobile phase) moves through a supporting medium (stationary phase), carrying the components of the mixture along with it. Due to the different strengths of
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