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Assuming equal concentrations and complete dissociation, rank these aqueous solutions by their freezing points. NH4l, CoBr3, Na2SO4

Whitney Matthews

in Chemistry

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Zach Chandler on January 7, 2019

Answer: NaI > Na2SO4 > Co Br3meaning that NaI has the highest freezing point, and Co Br3 has the lowest freezing point.Explanation:The freezing point depression is a colligative property.That means that it depends on the number of solute particles dissolved.The formula to calculate the freezing point depression of a solution of a non-volatile solute, is:ΔTf = i * Kf * mWhere kf is a constant, m is the molality and i is the van ' t Hoff factor.Molality, which is the number of moles per kilogram of solvent, which account for the number of moles dissolved and the van ' t Hoff factor multipllies according to molecules are dissociated.The greater the number of molecules that dissociate, the more high is the van ' t Hoff, the greater is the depression of the freezing point and lower the freezing point.As the question states that it assumes the equality of the concentrations (molality) and the complete dissociation you only have to find the number of ions generated for each solute, in this way:NH4 I → NH4(+) + I(-) => 2 ionsCo Br3 → Co(+) + 3 Br(-) => 4 ionsNa2SO4 → 2Na(+) + SO4(2-) => 3 ions.Thus, Co Br3 is the solute that generate more particles and the solution have the lower freezing point among the given choices, Na2SO4 is the side and the NaI is the third. Sort the freezing point of largest to smallest, the range is NaI > Na2SO4 > CoBr3, that is the answer given.


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