Assume that the molal freezing point depression constant of water is 1.86°C kg/m

Question

Assume that the molal freezing point depression constant of water is 1.86°C kg/mol and that the freezing point of water is 0.00°C.

a. Complete the following reaction showing what ions calcium chloride will produce upon dissolving in water. CaCl2(aq)

CaCl2(aq)-->

b.Calculate the molality (in m) of all solutes (that is, all ions in this problem) of 0.15 m calcium chloride aqueous solution. (Hint: You need to consider the stoichiometry in your answer for Problem 3-a).

c. Calculate both the freezing point depression (^T) and the freezing point of 0.15 m calcium chloride aqueous solution.

Explanation / Answer

a) CaCl2 + H2O ====> (Ca2+) + 2(Cl-) + H2O

b) molality of Ca2+ = molality of CaCl2 = 0.15m

molality of Cl- = 2*molality of CaCl2 = 0.3m

c) depression in freezing point = i*Kf*molality of CaCl2 = 3*1.86*0.15 = 0.837

therefore freezing point of CaCl2 solution is -0.837 degree celsius

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