BP - Two related colligative properties Boiling Point Elevation and Freezing Point Depression Boiling Point Elevation and Freezing Point Depression

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Boiling Point Elevation and Freezing Point Depression Two related colligative properties:
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Boiling Point Elevation and Freezing Point Depression The boiling point elevation is readily understood referring to Raoult’s law*. Consider a solvent with some solute that lowers the vapor pressure as in the figure. * If you’re unfamiliar with Raoult’s law, see the slideshow on the subject. 0 2 04 06 08 0 1 0 0 1 2 0 0 200 400 600 800 1000 1200 1400 t E C / E C pure solvent solvent with 0.05 mole fraction solute
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Boiling Point Elevation and Freezing Point Depression The boiling point elevation is readily understood referring to Raoult’s law*. Consider a solvent with some solute that lowers the vapor pressure as in the figure. 0 2 04 06 08 0 1 0 0 1 2 0 0 200 400 600 800 1000 1200 1400 95 96 97 98 99 100 101 102 103 104 105 600 650 700 750 800 850 900 Δ T b 1 atm t E C / E C t C / E C In order to maintain 1 atm vapor pressure over the solution, the temperature must be increased
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Boiling Point Elevation and Freezing Point Depression The boiling point elevation is readily understood referring to Raoult’s law*. Consider a solvent with some solute that lowers the vapor pressure as in the figure. 0 2 04 06 08 0 1 0 0 1 2 0 0 200 400 600 800 1000 1200 1400 95 96 97 98 99 100 101 102 103 104 105 600 650 700 750 800 850 900 Δ T b 1 atm t E C / E C t C / E C This increase in temperature is called the boiling point elevation, with the symbol Δ T b In order to maintain 1 atm vapor pressure over the solution, the temperature must be increased
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Boiling Point Elevation and Freezing Point Depression Similar arguement can be put forth for the freezing point depression.
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-6 -4 -2 0 2 4 0 1 2 3 4 5 6 7 Δ T f triple point t E C / E C Boiling Point Elevation and Freezing Point Depression Similar arguement can be put forth for the freezing point depression. This figure shows the depression in the triple point but the extra- polation to the 1 atm freezing point ( red and blue lines) yields a similar change. This is referred to as the freezing point depression and is given the symbol Δ T f .
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and bb f f TK b T K b Δ= Δ = Boiling Point Elevation and Freezing Point Depression In principle, one could calculate these effects given the equations for the lines in the illustrations. In practice, these are listed in handbooks using the equations: where K b and K f are constants depending upon the solvent and b is a concentration unit called “molality.”
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and bb f f TK b T K b Δ= Δ = with having the units of kg solute solvent n bm m = Boiling Point Elevation and Freezing Point Depression In principle, one could calculate these effects given the equations for the lines in the illustrations. In practice, these are listed in handbooks using the equations: where K b and K f are constants depending upon the solvent and b is a concentration unit called “molality.” Definition of molality:
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Boiling Point Elevation and Freezing Point Depression Example 1: What is the freezing point for a solution consisting of 100.0 g of benzene and 5.0 g of CH 3 CCl 3 ?
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This note was uploaded on 12/09/2011 for the course CHEM 1 taught by Professor Staff during the Summer '11 term at Simon Fraser.

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BP - Two related colligative properties Boiling Point Elevation and Freezing Point Depression Boiling Point Elevation and Freezing Point Depression

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