Question

What is the freezing point of a 1molal and 0.432molal `Zn(H2O)_6 ^(+2)`?

Answer 1

I'll do the 1 molal solution. You should then be able to do a 0.432 molal solution.

`DeltaT_f = T_f - T_f^"*" = -iK_fm`,

• `T_f` is the freezing point, of course, and `T_f^"*"` is that of water.
• `i` is the number of ions in solution. We ignore ion pairing for simplicity.
• `K_f = 1.86^@ "C/m"`
• `m` is the molality, traditionally in units of `"m"` or "molal".

Clearly, water is not an ion, and the hexahydrate acts as the simple cation in water. Thus, `i = 1`, and we simply have:

`DeltaT_f = T_f - 0^@ "C" = color(blue)(T_f)`

`= -(1)(1.86^@ "C/m")("1 m") = color(blue)(-1.86^@ "C")`