Cyclohexane is not a suitable solvent for ionic substances;water is used instead

Question

Cyclohexane is not a suitable solvent for ionic substances;water is used instead. The freezing point depression constant forwater is 1.858 degrees C/m. when ionic substances dissolve inwater, two or three ions per formula unit are often produced. ZnSO4(s) ---> Zn2+(aq) +SO42-(aq) Na2SO4(s) ---> 2 Na+(aq)+SO42-(aq) Freezing point depression is a colligative property and ittherefore deopends on the number of particles in the solution. Thusa solution of ZnSO4 should exhibit twice the freezingpoint depression as a solution of a molecular compound of the sameconcentration. A Na2SO4 solution should havethree times the effect. Calculate the molality of particles for each of the followingaqueous solutions of strong electrolyte. Which solution would havethe lowest freezing point? Explain. a) 0.03 m Al(ClO4)3 b) 0.05 m KNO3 c) 0.05 m Na2SO4 d) 0.03 m ZnCl2 Cyclohexane is not a suitable solvent for ionic substances;water is used instead. The freezing point depression constant forwater is 1.858 degrees C/m. when ionic substances dissolve inwater, two or three ions per formula unit are often produced. ZnSO4(s) ---> Zn2+(aq) +SO42-(aq) Na2SO4(s) ---> 2 Na+(aq)+SO42-(aq) Freezing point depression is a colligative property and ittherefore deopends on the number of particles in the solution. Thusa solution of ZnSO4 should exhibit twice the freezingpoint depression as a solution of a molecular compound of the sameconcentration. A Na2SO4 solution should havethree times the effect. Calculate the molality of particles for each of the followingaqueous solutions of strong electrolyte. Which solution would havethe lowest freezing point? Explain. a) 0.03 m Al(ClO4)3 b) 0.05 m KNO3 c) 0.05 m Na2SO4 d) 0.03 m ZnCl2 d) 0.03 m ZnCl2

Explanation / Answer

a) Al3+ and 3 ClO4-, so overall 4molecules. 4*0.03 = 0.12 m b) K+ and NO3- , so 2   2*0.05 = 0.1 m c) 2 Na+ and 1 SO42-   so 3*0.05 =0.15 m d) Zn2+ and 2 Cl-,   so 3*0.03 = 0.09 Na2SO4 has the highest concentration of the number of particles, soit will result in the lowest freezing point. (The freezing point ofa solution decreases as the concentration increases. The reason isthat the introduction of the new solutes hinder the interaction ofthe solvent molecules that want to form the solid phase, orfreeze)

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