Physical Separation of Mixtures

Experiment (2) Physical Separation of Mixtures Objectives: To separate a heterogeneous mixture based on each component's physical properties. A-Introduction: A mixture is a physical combination of two or more pure substances where each substance keeps its own chemical identity. For example, each substance in a salt-water mixture has the same chemical properties as its would have when pure, the water is present as H2O molecules and the salt is present as sodium ions (Na+) and chloride ions (Cl-). Mixtures are either homogeneous or heterogeneous. A homogeneous mixture is made up to two or more substances having uniform properties and composition throughout the mixture. mixture of gases. Air is an example of a homogeneous A heterogeneous mixture contains two or more separate phases. Today's experiment involves a heterogeneous mixture. The method chosen for separating the mixture is based on the differences in the chemical and/or physical properties of the mixture's components. Some common physical methods for separating a mixture's components include: a- Distillation: vaporizing a liquid from a solid (or another liquid) and condensing the vapor; b- Crystallization: Forming a crystalline solid decreasing its solubility as a result of cooling the solution, evaporating the solvent, or adding a solvent in which it is less soluble so that solid crystals from; c- Extraction: removing a substance from a solid or liquid mixture by adding a solvent in which the substance is more soluble; d- Filtration: removing a solid substance from a liquid by passing the suspension through a filter; e- Centrifugation: removing a solid substance from a solution by means of a centrifuge; f- Sublimation: vaporizing a solid and recondensing its vapor (not all solids sublime, however); In this experiment, you will separate an unknown mixture of NH4Cl, NaCl, and SiO2 using sublimation, extraction, and filtration methods. Some physical propertiiies of each chemical in the mixture are listed in Table-1 below. Table (1): Physical Properties of Some Pure Substances Compound Molar Mass NaCl 58.44 NH4Cl SiO4 Solubility (g/100 Melting Point Appearance 35 801 White crystals 53.49 37 Sublime at 340 White crystals 60.08 0.0 > 1600 White crystals g water at 25oC) B- Practice Exercise: A mixture weighs 9.8712g and contains 6.3164 grams of sodium chloride and 3.4779 grams of silicon dioxide. The remainder of the mixture is ammonium chloride. Calculate the percent by weight of each substance in the mixture. 1- Mass of mixture 9.8712 g 2- Mass of NaCl 6.3164 g 3- Mass of SiO2 3.4779 g 4- Mass of NH4Cl = mass of mixture – (mass of NaCl + mass of SiO2) = 0.0769 g 5- Percentage of NaCl = (Mass of NaCl/Mass of mixture) x 100% = 63.988% 6- Percentage of SiO2 = (Mass of SiO2/Mass of mixture) x 100% = 35.2335 7- Percentage of NH4Cl = (Mass of NH4Cl/Mass of Mixture) x 100% = 0.7790% C- Experimental Procedure: 1- Weigh a clean, dry, evaporating dish and record its mass on the report sheet. 2- Add about 2 g of the unknown mixture to the dish, weigh and record the mass. 3- Place the evaporating dish (with sample) on a wire gauze. 4- Heat the dish slowly, but gradually increase the heat until the white fumes of ammonium chloride stop vaporizing (approx. 15 minutes). 5- Cool the dish to room temperature, weigh, and record the mass on the report sheet. 6- Add about 20ml of distilled water to the solid in the evaporating dish and stir for about one minute. Decant the solution into a beaker. Add about 10 ml more of distilled water to the solid, stir again for about one minute, and decant into the beaker. Repeat once the 10 ml washing and decant them into the beaker. 7- Get a fine porosity filter paper, weigh two of them and seal it into a Buchner funnel with a small amount of distilled water. Have your instructor approve your filtering apparatus. Transfer the decanted solution in the beaker to the Buchner funnel. Rinse the solid with two sml portions of water. 8- First air-dry the solid on the filter paper, and then in a 100oC constant-temperature drying oven for about 10 minutes. 9- Allow to cool to room temperature, weigh, and record the mass on the report sheet. 10- At the end of the laboratory period, wash the funnel and the evaporating dish. Dispose of any sand in the waste beaker. Data and Results: A- Data Unknown No. …………….. 1- Mass of evaporating dish. ……………. g 2- Mass of evaporating dish and unknown ……………. g ……………. g 4- Mass of filter papers ……………. g 5- Mass of filter papers & the solid ……………. g 1- Mass of original mixture ……………. g 2- Mass of ammonium chloride in mixture ……………. g 3- Mass of sodium chloride in mixture ……………. g 4- Mass of silicon dioxide in mixture ……………. g 5- % NH4Cl in mixture ……………. % 6- % NaCl in mixture ……………. % 7- % SiO2 in mixture ……………. % mixture 3- Mass of evaporating dish & unknown mixture after heating B- Calculations and Results: * Show your calculations.