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 sodium bicarbonate solution exerts tonicity of 0.2024 mOsmol/ml. If the compound has a molecular weight of 84 g/mol, then express the concentration of the solution as percent w/v.


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lb equals 0.85 % kg

    For sodium bicarbonate , the 'golden formula' is:
    1 mmol = `[84]` mg = `[1]` mEq = `[2]` mOsmol.

    The solution contains 0.2024 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 0.2024 mOsmol is contained in 1 mL of solution, we keep the 0.2024 mOsmol in the numerator of the second fraction for getting the 'mOsmol' part cancelled out.
    Using dimensional analysis:

    `(84 \quad mg)/(2 \quad mOsmol) × (0.2024 \quad mOsmol)/(1 \quad mL) × (1 \quad g)/(1000 \quad mg)`

    ` × (100 \quad mL)/(100 \quad mL)= 0.85 \quad (g)/(100 \quad mL) => 0.85 % ` Ans.