negative ΔH°diss value will release more heat and thus result in a greater boiling point.
According to Table 1, magnesium sulfate has the most negative ΔH°diss value at −91.0
kJ/mol. Therefore, according to Student 3, this substance should have the greatest boiling
point of the substances listed.
6 . H Compare the new values given in the question to those for calcium chloride given in Table 1.
Cesium hydroxide produces 2 ions, while calcium chloride produces 3. Student 1 writes, The
solution containing Salt B had a higher boiling point because Salt B produces more ions
in solution than Salt A. According to this hypothesis, calcium chloride produces more ions,
so it should have a higher boiling point. The findings therefore support the hypothesis of
Student 1, eliminating (G) and (J). Cesium hydroxide has a molar mass 149.91 g/mol, while
calcium chloride has a molar mass of 111.0 g/mol. Student 2 writes, The solution containing
Salt B had a higher boiling point because it had a lower molar mass (the mass of 6.02 ×
1023 particles). According to this hypothesis, calcium chloride has a lower molar mass, so it
should have a higher boiling point. The findings therefore support the hypothesis of Student 2,
eliminating (F). There’s no need to test the findings against Student 3’s hypothesis: The only
option left is (H).
7 . C According to Student 2, the salt with the lower molar mass will result in more particles and a
greater solution boiling point than a salt with a greater molar mass. Student 2 is not
concerned with “enthalpy change,” so you can eliminate (B) and (D) immediately. According
to Table 1, sodium chloride has a molar mass of 58.4 g/mol, and ammonium nitrate has a
molar mass of 80.1 g/mol. Therefore, because sodium chloride has a smaller molar mass, it
should have a greater boiling point, as suggested in (C).
