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# n water - PowerPoint PPT Presentation

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651 g ethylenglycol,HOCH2CH2OH, are dissolved into 1.5 x 103 g water (a 30.3% w/w, solution, commonly used as antifreeze agent in cars cooling systems). What is the vapor pressure of the water over the solution at 90°C? Suppose water behaves in an ideal fashion, the vapor pressure of pure water at 90°C is 525.8 mmHg, and the molar mass of ethylern glycol is 62.07 g.

Data:651 grams solute, (HOCH2CH2OH), 1.5 x 103 g Solvent H2O,

Vapor pressure at 90°C = 525.8 mm Hg

Raoult’s law : P = csolvente Psolvente

c solvent is unknown, we must calkculate it:

csolvente =

Solvent over

the solution

Análisis dimensional:

nwater

[ ]

nwater = 1.50 x103 g

1 mole Water

= 83.2 mol

Nwater + nethylenglycol

18.02 g

1 mole ethylen glycol

]

nethylenglycol = 651g [

= 10.5 mol

62.07 g

cwater = 83.2 mole water

= 0.888

83.2 mole water + 10.5 mole ethylen glycol

P= 0.88 (525.8mm Hg) = 467 mm Hg

*The units are correct for the sought variable