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Chemistry LibreTexts

Groupwork 11 Ideal and nonideal systems

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    Work in groups on these problems. You should try to answer the questions without referring to your textbook. If you get stuck, try asking another group for help.

    At 90 ˚C, the vapor pressure of toluene is 400 torr while that of o-xylene is 150 torr. 

    • What is the composition of a liquid mixture that will boil at 90 ˚C when the external pressure is 0.5 atmosphere? 
    • What is the composition of the vapor? 
    • What assumptions have you made? 

    FYI:1 atm =760 torr

    Consider a mixture of 2,2,4-trimethyl pentane (iso-octane) and ethanol at 25 ˚C.  At 0.2748 mole fraction of iso-octane, the partial vapor pressure of iso-octane is 48.31 torr and the vapor pressure of pure iso-octane is 59.03 torr.  The partial vapor pressure of ethanol in the solution is 46.91 torr and the vapor pressure of pure ethanol is 49.31 torr.

    • Is the mixture ideal or nonideal?  If it is nonideal, does it deviate positively or negatively from ideality?  Explain your answer.
    • Could you ever have a solution where one component deviated positively from ideality and the other had a negative deviation?