What is P solution, the total vapor pressure, above this solution?ġ) Calculate the mole fraction of each substance:Ĭyclohexane ⇒ 1.40 mol / (1.40 mol + 2.50 mol) = 0.358974359Īcetone ⇒ 2.50 mol / (1.40 mol + 2.50 mol) = 0.641025641 The subscripts A and B stand for the two different volatile substances in the solution.Įxample #1: A solution is composed of 1.40 mol cyclohexane ( P cy o = 97.6 torr) and 2.50 mol acetone ( P ac o P solution = ( P A o) ( χ A ) + ( P A o) ( χ B ) The key equation to use is Raoult's Law, but in a slightly expanded form from how it is first presented: We will discuss the real behavior of solutions in a different tutorial. Also, note the presence of the word 'ideal' in the title. More complex solutions (with three or more volatile components) are discussed at a level beyond the scope of the ChemTeam's mission. 100% of the nonvolatile solute stays in solution, none of it enters the vapor above the solution.īy the way, at this introductory level, we will only discuss solutions with two volatile components. In a solution with a nonvolatile solute, only the pure vapor of the solvent is present above the solution. The key point to remember about solutions with two (or more) volatile components? All the components are represented in the vapor that is in contact with the solution. Raoult's Law: Vapor Pressure and Volatile Solutes (in Ideal Solutions) Raoult's Law: Vapor Pressure and Volatile Solutes (in Ideal Solutions)
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