Type 3: Determine percent strength from osmolarity of the solution

5. mEq and mOsmol 5.2) mOsmol 5.2.1) mOsmol - General

5.2.1.1) mOsmol - General Normal 1


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A penicillin V potassium solution exerts tonicity of 0.1005 mOsmol/ml. If the compound has a molecular weight of 388 g/mol, then express the concentration of the solution as percent w/v.


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lb equals 1.95 % kg

    For penicillin V potassium , the 'golden formula' is:
    1 mmol = `[388]` mg = `[1]` mEq = `[2]` mOsmol.

    The solution contains 0.1005 mOsmol per 1 mL.
    Since we need g quantity in the numerator of the desired unit, we begin with keeping the mg unit in the numerator of the first fraction.
    Again, since 0.1005 mOsmol is contained in 1 mL of solution, we keep the 0.1005 mOsmol in the numerator of the second fraction for getting the 'mOsmol' part cancelled out.
    Using dimensional analysis:

    `(388 \quad mg)/(2 \quad mOsmol) × (0.1005 \quad mOsmol)/(1 \quad mL) × (1 \quad g)/(1000 \quad mg)`

    ` × (100 \quad mL)/(100 \quad mL)= 1.95 \quad (g)/(100 \quad mL) => 1.95 % ` Ans.


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