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Experiment 12 – Freezing Point of Solutions A solution freezes at a lower temperature than does the pure solvent. This phenomenon is called freezing point depression. The freezing point depression ofa solution is a colligative property of the solution which is dependent upon the number of dissolved particles in the solution. The higher the solute concentration, the greater the freezing pointdepression of the solution. The freezing point plot of a pure solvent and a solution are shown below:

The freezing point of the pure solvent is at constant temperature but the freezing point of thesolution slowly decreases. The decrease caused by the increase in solute concentration as the solvent freezes. The dissolved solutes can be non-electrolytes or electrolytes. Non-electrolytes aremolecules that remain intact when they dissolve in water. Electrolytes are solutes that dissociate into ions when dissolved in solution to give an electrically conducting solution. The equation describingthe change in freezing point from pure solvent to solution is: Tf = Kf m (non-electrolytes) Tf =i Kf m (electrolytes) Kf is the molal freezing point depression constant of the solvent (1.86 °C/m forwater). m = molality = moles of solute per kilogram of solvent. i = the number of dissolved particles (Van’t Hoff Factor). In this experiment, the freezing points of aqueous solutions of methanol, anon-electrolyte, and sodium chloride, an electrolyte, will be measured and the molality of each solution will be calculated.

Equipment and Reagents 8 inch test tube Stirring apparatus ThermometerProcedure 1. Place 10 mL of distilled water in an 8 inch test tube. Insert the stirring apparatus as shown in the Figure below. Make sure that the thermometer bulb is immersed in the liquid. 2. Placethe entire apparatus in a salt ice-bath. Allow the water to cool with continuous stirring until there is an ice-water slush in the tube. rubber stopper with hole distilled water rock salt methanol in...
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