Chemistry

How many grams of water are needed to dissolve 27.8g of NH4NO3 (80.0 g/mol) in order to prepare a 0.452 m (molal) solution?

27.8g / 80g/mol X 0.452 = 0.157

Is this correct?

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  1. I think you algebra is off somewhere. Moles is correct but not kg solvent.
    27.8 g/80 = ? moles.
    m = ?moles/kg solvent
    Solve for kg solvent.
    You can check yourself to see if it is right. 27.8/80 = about 0.35
    0.35/0.157 = about 2.2m which isn't 0.452.

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  2. the answer choices that were given are:

    a)769g
    b)36.2g
    c)972g
    d)34.8g
    e)157g

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  3. I can assure you that 157 g is not right.
    C'mon Hannah, do the math.
    27.8/80 = ?mols
    m = moles/kg solvent so
    kg solvent = moles/m and that isn't 0.157 kg.

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  4. 27.8/80=0.3475 but I don't understand what to do next.

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  5. You have 27.8 g NH4NO3.
    mol NH4NO3 = 27.8/80 = 0.3475
    You want a molality of 0.452
    m = 0.452 = moles/kg solvent
    0.452 = 0.3475/kg solvent
    Solve for kg solvent.
    Then since the answers are given in grams, you will need to convert kg solvent to g solvent.

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  6. Ok thank you

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