Question

Logan is cooking, and he wants to increase the boiling point of the water. Which solute would not be a good choice as it would not increase the boiling point as much as the others?
A. Salt, NaCl

B. Magnesium Sulfate, MgSO4

C. Potassium Sulfate, K2SO4

D. Sucrose, C12H22O11

Answer 1

Sugar would not increase the boiling point of the water as much as the others.To show this, we recall the equation for boiling point elevation ∆t:  
     ∆t = i Kb m 

The difference in these four solutions will be in the product of the van't Hoff Factor i and molality m: i * m. 

If we assume that we have 0.1m of each solute, the products i*m for these solutions are:
     
     Solution                      Identity of particles                          i      i * m
        0.1 m NaCl                 Na+, Cl-                                         2     2 * 0.1 = 0.2
        0.1 m MgSO4             Mg^2+, SO4^2-                            2     2 * 0.1 = 0.2
        0.1 m K2SO4              two K+, SO4^2-                           3     3 * 0.1 = 0.3
        0.1 m C12H22O11      covalently bonded molecules     1     1 * 0.1 = 0.1

Therefore, having the lowest  i * m, sucrose will have the lowest boiling point elevation.