Question

Winter is here and Jon, Bran, and Rickon all have identical icy drawbridges. Jon buys 10 kg of NaCl, Bran buys 10 kg of CaCl2 and Rickon buys 10 kg of MgCl2. Assuming that ideal dissociation of the salts occurs and colligative properties are the only consideration, whose drawbridge will thaw most effectively?

A. Jon's
B. Bran's
C. Rickon's
D. All three drawbridges will deice to the same extent
E. Bran and Rickon's drawbridges will deice better than Jon's

Answer 1

Bran's and Rickon's drawbridges will thaw most effectively because calcium chloride (CaCl2) and magnesium chloride (MgCl2) dissociate into three ions each, compared to sodium chloride (NaCl) which only dissociates into two ions, resulting in a greater freezing point depression.

Step-by-step explanation:

When considering the effectiveness of salts used for thawing icy drawbridges, the key concept to understand is freezing point depression, which is one of the colligative properties. This property depends on the number of particles (ions) that a compound dissociates into when it dissolves in water. Sodium chloride (NaCl) dissociates into two ions (Na+ and Cl−), while calcium chloride (CaCl2) and magnesium chloride (MgCl2) each dissociate into three ions (Ca2+ or Mg2+ and two Cl− ions). Therefore, mole for mole, CaCl2 and MgCl2 would have a 50% more impact on freezing point depression than NaCl

In this scenario, both Bran's drawbridge (which uses CaCl2) and Rickon's drawbridge (which uses MgCl2) will thaw most effectively as compared to Jon's drawbridge (which uses NaCl), due to the higher number of particles produced upon dissociation of CaCl2 and MgCl2.