Calculate the molality of a solution made by dissolving a compound in camphor if the freezing point of the solution is 162.33 degrees C: the melting point of pure camphor was measured to be 178.43 degrees C. K sub f for camphor is 37.7 degrees C/m sub c?
Please explain the equation used for this problem and how to get to the answer. The answer isn't needed to be provided.
Please explain the equation used for this problem and how to get to the answer. The answer isn't needed to be provided.
1 Answer
Explanation:
To make any sense of this question, let's first write down what we are given.
Given



Well first off, we should understand the concept being tested  colligative properties.
Colligative properties describe the physical properties of solutions that depend only on the amount of solutes dissolved in solutions and not the type dissolved. Here, melting point/freezing point is being affected. When you add solutes to a pure solution, the freezing point of the solution decreases.
Clearly, the pure camphor and the camphor with the added compound have different freezing points.
To find the molality of the compound we need the following formula
Where
#DeltaT = "change in the temperature" (color(white)(a)^@C)# #i = "vant Hoff factor"# #K_f = "molal freezing point constant" ((color(white)(a)^@C)/(m))# #m = "molality" ("moles of solute"/"1 kg of solvent" or m)#
The vant Hoff factor of a nonelectrolyte solute is 1.
Plugin, rearrange and solve (ignored units for simplicity sake)

#color(magenta)(DeltaT = iK_(f)m)# 
#16.10 = (1)(37.7)(m)# 
#(16.10)/[(1)(37.7)] = m# 
#"molality" = 0.42" m, where m equals molal"#