Anonymous
Anonymous asked in Science & MathematicsChemistry · 1 month ago

What is the molality of an ethanol-water solution if 64.3mL of ethanol(CH3CH2OH, d = 0.789 g/cm3) is added to 25.9g of water(d = 1.00 g/mL)?

A. 

53.2 m

B. 

0.0425 m

C. 

36.2 m

D. 

42.5 m

E. 

67.4 m

3 Answers

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  • 1 month ago

    What is the molality of an ethanol-water solution if 64.3mL of ethanol(CH3CH2OH, d = 0.789 g/cm3) is added to 25.9g of water(d = 1.00 g/mL)?

    Density = Mass/ Volume

    Mass of water=

    Volume of water× density 

    =64.3×0.789

    = 81.50 gm

    Molar mass of ethanol/ Weight

    46/0.0259=

    1776.0617760617

    Apply about value in formula of molality= wt of solute / weight of solvent

  • Dr W
    Lv 7
    1 month ago

    molality = moles solute / kg solvent

    in this particular case, I'd argue the ethanol was the solvent.  There's 2.5x as much EtOH as H2O 

    so that

    .. 25.9g H2O... .. 1 mol H2O.. .. 1 mL EtOH. .. .1000g

    ---- ---- ---- ----- x ----- ----- ----- x ----- ----- ----- x ---- ----- = 28.3m

    . 64.3mL EtOH.. 18.02g H2O.. .0.789g EtOH.. ..1 kg

    ********

    but.. that's not one of the choices is it?  so let's see what happens if we...  for God only knows why... assume H2O is the solvent

    .. 64.3mL EtOH.. . 0.789g EtOH.... 1 mol EtOH... .. 1000g 

     ---- ----- ---- ----- x ---- ---- ---- ---- x ---- ---- ---- ---- x ---- ----- = 42.5m

    .. .25.9g H2O.. .. ... .1 mL EtOH.. . 46.07g EtOH.. . .. 1 kg

  • 1 month ago

    (64.3 mL) x (0.789 g/mL) / (46.0684 g ethanol/mol) / (0.0259 kg) = 42.5 mol / kg =

    42.5 m

    So answer D.

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