Q. Iron chloride forms various solid hydrates, all of which melt congruently. The temperatures t of aqueous solutions of various compositions that are saturated with respect to a solid phase.

(a) Use these data to construct a t-z_B phase diagram for the binary system of FeCl₃ (A) and H₂O (B). Identify the formula and melting point of each hydrate.

Hint: derive a formula for the mole ratio n_B = n_A as a function of x_A in a binary mixture.

(b) For the following conditions, determine the phase or phases present at equilibrium and the composition of each.

1. t = 70.⁰C and z_A = 0.100

2. t = 50.⁰C and z_A = 0.275