Question

What aqueous solution has the highest boiling point at standard pressure? A) 1.0 M KCl(aq) B) 1.0 M CaCl2(aq) C) 2.0 M KCl(aq) D) 2.0 M CaCl2(aq)

Answer 1

The increase in the boiling point of a solvent is a colligative property.


That means that the increase in the boling point will be related to the number of particles (molecules or ions) present in the solution.


The higher the number of particles (molecules or ions) the higher the increase in the boiling point.


All the aqueous solutions presented are electrolytes, i.e. the solutes are ionic compounds.


Then, you have to compare the number of ions that you have in each solution.


A) 1.0 M KCl ---> 1.0 M K+     +      1.0 MCl-    = 2 moles of particles / liter


B) 1.0 M CaCl2 --> 1.0M Ca(2+)      +      1.0M * 2 Cl (-)    = 3 moles of particle / liter


C) 2.0M KCl ---> 2.0 M K+      +      2.0 M Cl-  = 4 moles of particle / liter


D) 2.0 M CaCl2 ----> 2.0 M Ca (2+)      + 2.0M * 2 Cl (-)  = 6 moles of particle / liter.


Then, the solution 2.0M CaCl2(aq) has the highest increase in the boiling point.


Answer: option D) 2.0 M Ca Cl2(aq)