Passage III

A mole is 6 x 1023 molecules or formula units of a compound. Thus, the number of sucrose molecules in 1 mole of sucrose equals the number of NaCl units in 1 mole of NaCl. Molality (m) is a unit of concentration defined as:

When a substance is dissolved in a solvent, the freez­ing and boiling points of the solution will differ from those of the pure solvent. These changes depend on the concentration­ show how the freezing point and the boiling point, respec­tively, of H2O at 1 atm of pressure vary with concentration for 3 solutes.

13. Based on the trends in Figure 2, which of the following aqueous solutions would have the highest boiling point ?

Answer and Explanation

Your Answer is

Correct Answer is A

Explanation

Put value questions. See figure 2, whenever the concentration concentration of CaCl2 solution increases by 0.8, the boiling point increases by 1.2 °C;

When the concentration concentration of NaCl solution increases by 0.8, the boiling point increases approximately 0.8 °C;

When the concentration of sucrose solution increases by 0.8, the boiling point increases by approximately 0.4 °C.

Therefore, the corresponding boiling point of 1.20 m CaCl2 solution is about 101.8°C, the corresponding boiling point of 1.4 m NaCl solution is about 101.4°C, and the corresponding boiling point of 1.6 m sucrose solution is about 100.8 °C, 1.8 m sucrose solution corresponds to a boiling point of about 100.9°C, the highest boiling point is 1.2 m CaCl2