Passage I

The freezing point of an aqueous solution (Tf), in °C, can be calculated using the equation

Tf = −1.86 × m × i

where m is the concentration of the solute in moles of solute per kilogram of H2O (mol/kg H2O) and i is the average number of particles produced by 1 formula unit of the solute when the formula unit dissolves in H2O. The theoretical i value of a solute is the total number of particles produced when 1 formula unit of the solute dissolves in H2O. Table 1 gives, for 4 ionic compounds, the chemical formula and the theoretical i value. Table 2 shows how the observed i value at 25°C for these compounds changes with solute concentration.

Table 2 adapted from B. A. Kunkel, “Comments on ‘A Generalized Equation for the Solution Effect in Droplet Growth.’ ” ©1969 by American Meteorological Society.

4. Based on Tables 1 and 2, which ionic compound has the largest deviation from its theoretical i value at a concentration of 2.0 mol/kg H2O ?

Answer and Explanation

Your Answer is

Correct Answer is H

Explanation

This question needs to subtract the absolute value of the value in Table 2 when the H2O unit is 2.0 from the value in Table 1 to obtain the deviation of each chemical component. NaCl is |2 -1.97|=0.03, KCl is |2-1.83|=0.17, MgCl2 is |3-4.57|=1.57, (NH4)2< /sub>SO4 is |3-1.87|=1.13, so the largest deviation is MgCl2