Question

10. The phase diagram for the mixtures of Pt and Au at 1 atm is given to the right. (a) Give a complete description of the system at point P. (b) Mark on the diagram the path of cooling a melt of 50% Pt from 1700°C to 1000°C. Use a red line for the liquid phase and a blue line for the solid phase. (C) A 10 kg melt of 50% Pt is cooled from 1700°C to 1400°C. Assuming equilibrium is kept at all times, what is the weight of Pt in the solid phase at the final temperature? 0 20 40 60 80 100 % Pt

Answer 1

a)

Point P represents a system of 70% Pt and 30% Au at 1400 °F.

TC 1600 Liquid Curve 1400 L A 1200 Solid Curve 0 20 40 60 80 100 %

At equilibrium, the mixture separates into two phases:

• Solid Phase (Point B) contains ~80% Pt
• Liquid Phase (Point A) contains ~28% Pt

b)

Initial mixture is represented by point A. Final mixture is represented by point B.

T, с 1600 1400 1200 1000 о 20 40 60 80 100 %Р

c)

496 007 08 09 ΟΜ οτ ο 1200 1400 1600 T, C

Initial mixture is represented by point A. At 1400 °F, Liquid phase is represented by point B and solid phase is represented by point C.

Weight of Pt in initial mixture = 50 * 10 / 100 = 5 kg

Point C contains 80% Pt in solid state. Point B contains 25% Pt in liquid state.

Let x kg of mixture exists in solid phase. (10 – x) kg exists in liquid phase.

Mass Balance:

x * 80/100 + (10 – x) * 25/100 = 5 kg

55 x = 500 – 250

x = 250/55 = 50/11 kg

Weight of Pt in solid phase = x * 80/100 kg

= 50/11 * 80 / 100 = 3.64 kg