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Chem II

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When you are given the question: Arrange the following aqueous solutions in order of increasing boiling points. 0.050 m Mg(NO3)2; 0.100 m ethanol; and 0.090 m NaCl.

I know the formula for boiling point, but I don't know where to get the Kb. Am I headed in the right direction?

  • Chem II -

    Actually you don't need Kb, although it is 0.51 degrees/molal for water. Look at the formula which is delta T = i*Kb*m
    i is the number of particles. m is the molality, Kb is a constant.
    So look at the product of i*m and see which is larger. As i*m*Kb increases, delta T increases and the boiling point increases. Since you are interest ONLY in the order, and not the exact boiling point, Kb doesn't matter.
    Mg(NO3)2 has 3 particles; i.e., 1 Mg and 2 nitrate ions.
    NaCl has 2 particles; i.e., 1 Na and 1 Cl^-. Etc.

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