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**Problem**: Sulfuric acid in water dissociates completely into H+ and HSO4- ions. The HSO4- ion dissociates to a limited extent into H+ and SO42-. The freezing point of a 0.1000 m solution of sulfuric acid in water is 272.72 K.Calculate the molality of SO42- in the solution, assuming ideal solution behavior.

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We’re being asked to find the molality of SO_{4}^{2-} solution assuming ideal behavior.

When calculating the freezing point of a solution, we’re going to use the equation for Freezing Point Depression.

$\overline{){\mathbf{\u2206}}{{\mathbf{T}}}_{{\mathbf{f}}}{\mathbf{=}}{\mathbf{i}}{\mathbf{\xb7}}{{\mathbf{K}}}_{{\mathbf{f}}}{\mathbf{\xb7}}{\mathbf{m}}}$

∆T_{f} = change in freezing point = T_{f pure solvent} –T_{f solution}

K_{f} = freezing point depression constant

i = van' t Hoff factor of the solute = no. of ions

m = molality

Recall that the formula for **molality **is:

$\overline{){\mathbf{Molality}}{\mathbf{,}}{\mathbf{}}{\mathbf{m}}{\mathbf{=}}\frac{\mathbf{moles}\mathbf{}\mathbf{solute}\mathbf{}\mathbf{\left(}\mathbf{mol}\mathbf{\right)}}{\mathbf{kilogram}\mathbf{}\mathbf{solvent}\mathbf{}\mathbf{\left(}\mathbf{kg}\mathbf{\right)}}}$

Determine the required values for the Freezing Point Depression equation:

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Sulfuric acid in water dissociates completely into H^{+} and HSO_{4}^{-} ions. The HSO_{4}^{-} ion dissociates to a limited extent into H^{+} and SO_{4}^{2-}. The freezing point of a 0.1000 m solution of sulfuric acid in water is 272.72 K.

Calculate the molality of SO_{4}^{2-} in the solution, assuming ideal solution behavior.

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Our tutors have indicated that to solve this problem you will need to apply the Freezing Point Depression concept. You can view video lessons to learn Freezing Point Depression Or if you need more Freezing Point Depression practice, you can also practice Freezing Point Depression practice problems .

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