An analytical chemist is investigating two samples of sulfur, X and Y, to determine their relative purity. They heat both samples at a constant rate and record their temperature over time, as shown in the heating curve below:
Which of the following conclusions is correct regarding the purity and melting behavior of the two samples?
Sample X is pure as it has a sharp melting point of 114∘C114^\circ\text{C}114∘C. Sample Y is impure because the impurities disrupt the regular structure, lowering the melting point and causing it to melt over a range of 105∘C105^\circ\text{C}105∘C to 112∘C112^\circ\text{C}112∘C.
Sample Y is pure as it starts to melt at a lower temperature (105∘C105^\circ\text{C}105∘C). Sample X is impure because the impurities strengthen the crystal lattice, causing it to melt at a higher, sharp temperature of 114∘C114^\circ\text{C}114∘C.
Sample X is impure because the presence of impurities raises the melting point to 114∘C114^\circ\text{C}114∘C. Sample Y is pure because melting over a broad range (105∘C105^\circ\text{C}105∘C to 112∘C112^\circ\text{C}112∘C) allows different parts of the pure crystal lattice to melt sequentially.
Sample Y is pure because the range 105∘C105^\circ\text{C}105∘C to 112∘C112^\circ\text{C}112∘C represents a state of equilibrium. Sample X is impure because impurities cause the entire structure to collapse simultaneously at a single temperature of 114∘C114^\circ\text{C}114∘C.