Question

Shown below is an isobaric binary temperature-composition phase diagram in the system X-Y with complete miscibility between X and Y. 

 

• A. The first formed crystal has a composition of X₂₀Y₈₀.
• B. The final melt composition during equilibrium crystallization is X₆₀Y₁₀.
• C. In case of fractional crystallization, the final melt is enriched in X than X₉₀Y₁₀.
• D. For fractional crystallization, the final crystal composition is X₆₀Y₄₀.

Hint:

In fractional crystallization, the first crystals tend to be enriched in the component with the lower melting point, while equilibrium crystallization leads to a melt that is enriched in the more refractory component.

Answer 1

The Correct Option is A, B, C

Step 1: Understanding the question.
The question refers to a binary temperature-composition phase diagram and asks for the crystallization behavior of a starting melt with a composition of X₆₀Y₄₀. We are concerned with fractional crystallization and equilibrium crystallization.
Step 2: Analyzing the options.
(A) The first formed crystal has a composition of X₂₀Y₈₀: Correct — During fractional crystallization, the first crystal to form is typically richer in one component, in this case X₂₀Y₈₀.
(B) The final melt composition during equilibrium crystallization is X₆₀Y₁₀: Correct — In equilibrium crystallization, the final composition of the melt is typically enriched in the more refractory component, in this case Y.
(C) In case of fractional crystallization, the final melt is enriched in X than X₉₀Y₁₀: Correct — As the crystallization proceeds, the melt becomes progressively enriched in X, leading to a final melt composition like X₉₀Y₁₀.
(D) For fractional crystallization, the final crystal composition is X₆₀Y₄₀: Incorrect — The final crystal composition after fractional crystallization is typically not the same as the original composition, as the crystals become enriched in one component over time.
Step 3: Conclusion.
The correct answer is (A), (B), (C). These statements correctly describe the behavior of the system during crystallization.