What mass of C2H5OH should be added to 658 kg paraffin mixture if the vap pressure of ethanol @35°C …

Posted on September 20, 2010 by admin 1

A "canned heat" product used to warm chafing dishes consists of a homogeneous mixture of ethanol, C2H5OH, and paraffin that has an average formula C24H50. The vapor pressure of pure ethanol at 35°C is 100 torr.

Chafing Dishes:

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1 response to What mass of C2H5OH should be added to 658 kg paraffin mixture if the vap pressure of ethanol @35°C …

  1. shivaran...
    September 30, 2011 at 22:59

    If we suppose that mixture is an ideal solution, Raoult's Law can be applied :

    pi = pi* . xi

    With
    pi : the partial pressure of component i
    pi* : the vapor pressure of component i
    xi : the mole fraction of component i in solution

    Molecular weights :
    C2H5OH : 46 g/mol
    C24H50 : 338 g/mol

    p(EtOH) = p(EtOH)* . x(EtOH)
    8 = 100 . x(EtOH)
    x(EtOH) = 0.08

    Nb of moles of (C24H50) : n(C24H50) = 658 / 338 = 1.95 mol

    x(EtOH) = n(EtOH) / [ n(EtOH) + n(C24H50) ]
    0.08 = n(EtOH) / [ n(EtOH) + 1.95 ]

    n(EtOH) = (0.08*1.95) / (1 – 0.08) = 0.17 mol

    m(EtOH) = 0.17*46 = 7.82 g

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