The molal boiling-point constant for water is 0.51°C/molal.The boiling point of a 1.00 m solution of Ca(NO₃)₂ should be increased by A)exactly 1.53°C. B)exactly 1.02°C. C)somewhat less than 1.02°C. D)exactly 0.51°C. E)somewhat less than 1.53°C.

Question

Quizplus · Accepted Answer

The correct answer involves understanding the concept of boiling point elevation and the van't Hoff factor (i), which accounts for the number of particles a solute dissociates into in solution. Calcium nitrate, Ca(NO3)2, dissociates into three ions: one Ca2+ and two NO3-. Therefore, the van't Hoff factor (i) is 3. However, due to ion pairing and other interactions in real solutions, the effective increase in boiling point is often less than the theoretical value calculated using the ideal van't Hoff factor. Thus, the boiling point elevation will be somewhat less than 1.53°C (0.51°C/molal * 3), making E the correct choice.

The Molal Boiling-Point Constant for Water Is 0