Colligative properties of nonelectrolyte solutions

The colligative properties of nonelectrolyte solutions provide a means of determining the molar mass of a solute. Theoretically, any of the four colligative properties... 

So far we have discussed the colligative properties of nonelectrolyte solutions. Because electrolytes undergo dissociation when dissolved in water [W Section 4.1], we must consider them separately. Recall, for example, that when NaCl dissolves in water, it dissociates into Na Co ) and C aq). For every mole of NaCl dissolved, we get two moles of ions in solution. Similarly, when a formula unit of CaCL dissolves, we get three ions one Ca ion and two Cl ions. Thus, for every mole of CaCl2 dissolved, we get three moles of ions in solution. Colligative properties depend only on the number of dissolved particle.s—not on the type of particles. This means that a 0.1 m solution of NaCl will exhibit a freezing point depression twice that of a 0.1 m solution of a nonelectrolyte, such as sucrose. Similarly, we expect a 0.1 m solution of CaCL to depress the freezing point of water three times as much as a 0.1 m sucrose solution. To account for this effect, we introduce and define a quantity called the van t Hoff factor (i), which is given by... 

For example, when 1 mol of NaCl dissolves in water, it forms 1 mol of dissolved Na" ions and 1 mol of dissolved CF ions. Therefore, the resulting solution has 2 mol of dissolved particles. The colligative properties of electrolyte solutions reflect this higher concentration of dissolved particles. In this section we examine colligative properties of nonelectrolyte solutions we then expand the concept to include electrolyte solutions in Section 12.7. 

Why is the discussion of the colligative properties of electrolyte solutions more involved than that of nonelectrolyte solutions ... 

Describe electrolyte behavior and the four colligative properties, explain the difference between phase diagrams for a solution and a pure solvent, explain vapor-pressure lowering for nonvolatile and volatile nonelectrolytes, and discuss the van t Hoff factor for colligative properties of electrolyte solutions ( 13.5) (SPs 13.6-13.9) (EPs 13.59-13.83)... 

Explain why colligative properties of electrolyte solutions are more difficult to calculate than for nonelectrolyte solutions. 

Solutions of Electrolytes—Calculating colligative properties of electrolyte solutions is more difficult than for solutions of nonelectrolytes. The solute particles in electrolyte solutions are ions or ions and molecules. Calculations using equations (14.5) and (14.6) must be based on the total number of particles present, and the van t Hoff factor is introduced into these equations to reflect this number. In all but the most dilute solutions, composition must be in terms of activities— effective concentrations that take into accoimt interionic forces. 

The properties of a solution differ considerably from those of the pure solvent Those solution properties that depend primarily on the concentration of solute particles rather than their nature are called colligative properties. Such properties include vapor pressure lowering, osmotic pressure, boiling point elevation, and freezing point depression. This section considers the relations between colligative properties and solute concentration, with nonelectrolytes that exist in solution as molecules. 

As noted earlier, colligative properties of solutions are directly proportional to the concentration of solute particles. On this basis, it is reasonable to suppose that, at a given concentration, an electrolyte should have a greater effect on these properties than does a nonelectrolyte. When one mole of a nonelectrolyte such as glucose dissolves in water, one mole of solute molecules is obtained. On the other hand, one mole of the electrolyte NaCl yields two moles of ions (1 mol of Na+, 1 mol of Cl-). With CaCl three moles of ions are produced per mole of solute (1 mol of Ca2+, 2 mol of Cl-). 

In this section, we focus most of our attention on the simplest case, the colligative properties of solutes that do not dissociate into ions and have negligible vapor pressure even at the boiling point of the solvent. Such solutes are called nonvolatile nonelectrolytes sucrose (table sugar) is an example. Later, we briefly explore the properties of volatile nonelectrolytes and of strong electrolytes. 

Colligative Properties of Solutions Nonvolatle Nonelectrolyte Solutions Solute Molar Mass Vdatle Nonelectrolyte Solutions Strong Electrolyte Solutions... 

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