Chemistry Question. Please Help!!!?

The solubility of compound A in ethanol is 0.5 g per 100 mL at 0 degrees Celsius and 5.0 g per 100 mL at 78 degrees Celsius. a) To make a hot saturated solution of 15.0 g of A at 78 degrees Celsius, how much ethanol is required? b) When the solution prepared in (a) is cooled to 0 degrees Celsius, how much of compound A will be crystallized? How much of A would remain in solution and would not be recoverable.

If you could please help me solve this I would be most appreciative. I'm going to speak to a tutor as soon as a I can to see if they can help me as well. I'm able to answer everything else but I don't know where to start with this one. Please help!

1 Answer

  • HPV
    Lv 7
    9 years ago
    Favorite Answer

    The stated solubility of compound A in ethanol at 78C is 5.0 g / 100 mL. So if you want to dissolve 15.0 g of A in ethano, at 78C,

    5.0 g A.......15.0 g A

    ------------ = --------------

    100 mL.........x mL

    It's just a simple proportion problem. x = 300 mL.

    When you cool that solution to 0 C, only 0.5 g A / 100 mL will stay dissolved. Since you have 300 mL,

    0.5 g..........x g A

    ----------- = --------------

    100 mL.....300 mL

    x = 1.5 g, which means that the rest of the 15.0 g (15.0 - 1.5 = 13.5 g) will crystallize out.

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