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UI CHEM 1120 - Colligative Properties such as freezing point depression, boiling point elevation, and osmosis
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CHEM 1120 1st Edition Lecture 3 Outline of Last Lecture I. Solution Process and EntropyII. Gas Solubility, Pressure, and TemperatureIII. Units of ConcentrationIV. Colligative PropertiesOutline of Current Lecture I. Continuing with Colligative Properties, Freezing Point DepressionII. Boiling Point ElevationIII. OsmosisCurrent Lecture I. i = van’t hoff factor (2 when a substance ionizes, usually 1) △Tb = ikb m △Tb = boiling point elevation kb = molal boiling point elevation constant m = molality△Tf = -ikf m △Tf = freezing point depression kf = molal freezing point depression constant*Note that the constants for each equation differ for different solvents.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Example: Vinegar is essentially a 5.0% (w/w) solution of acetic acid (HC2H3O2)in water. What is the freezing point of vinegar? kf = 3.90 (acetic acid), 1.86 (water) (units = degrees C/m)Solution: Assume 1 kg of solution= 0.95 kg water= 0.05 kg = 50 g acetic acid(50 g)/(60.05g/mol) = 0.8326 mol acetic acid molality = (0.8326 mol)/(0.95 kg) = 0.8764 m △Tf = -ikf m = (1.86)(0.8764) = -1.63 degrees CII. Example: Seawater is about 3.5% NaCl. Calculate the normal boiling point of seawater. kb = 0.51Assume 100 g of solution = 3.5 g NaCl= 96.5 g water 3.5 g NaCl x (1 mol /58.5 g/mol) = 0.0598 mol m = 0.0598 mol/0.0965 kg = 0.612 m △Tb = ikb m = 2 x 0.51 x 0.612 = 0.64 degrees C ——> 100 + 0.64 = 106.4 degrees CIII. Osmosis is described as the diffusion of solvent through a semi-permeablemembrane into a solution of higher concentration. A semi-permeable membrane is a membrane that only allows certain solvent molecules to go through to the other side of the membrane, but not solute molecules. Some examples of osmosis are:• nutrient transport in plants and animals• carrots regain crispness in water• meat is preserved in salt cucumbers shrivel to become pickles in brineOsmotic Pressure (π) = the pressure resulting from osmosis and equal to the minimum counter pressure necessary to prevent osmosis. Osmotic pressurescan get very high.Similar to Ideal Gas Law: π=MRT M = molarity, R = 0.08206, T in KelvinExample: What is the osmotic pressure of a 1.0 M sucrose solution at room temperature (20 degrees C)?Solution:π = MRT= (1 mol/L) x (0.08206 L*atm/mol*K) x 293 K= 24 atmIf the osmotic pressure is the same on both sides of a membrane (concentrations are equal), the solutions are considered isotonic. If the solute concentration outside the cell is greater than that inside the cell, the solution is hypertonic. Water will flow out and crenation,contraction of a cell after exposure to a hypertonic solution due to the loss ofwater through osmosis, will occur. If the solute concentration outside the cell is less than the solute concentration inside the cell, the solution is hypotonic. Water will flow into the cell and hemolysis, rupturing of the cell, which then releases its contents and fluids into the surrounding fluid, will


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UI CHEM 1120 - Colligative Properties such as freezing point depression, boiling point elevation, and osmosis

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