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Unformatted text preview: Lecture 14: Getting Quantitative About Solubility Our last lecture on simple equilibria concerns what happens when you throw a salt that can dissociate into water and try to assign some numbers to the amount of material that dissolves. We will find that a process similar to what we did using the RICE expression applied to dissociating acids and bases will apply here as well, and that the notion of strong and weak acids have parallels to soluble and slightly soluble salts. We will also see that the strategies for simplifying the equilibrium problem by making approximations will allow us to create very simple calculation strategies. So as much as anything, look for parallels to acid/base equilibria to help reinforce your understanding of dissociation equilibria. Throwing salts in waterour qualitative background. What we have learned three different ideas over the course of the year that can explain solubility: 1. The solubility rules. These include facts such as: ! CO 3 2- , S 2- , OH- , PO 4-3 dont dissolve ! K + , Na + , NO 3- , NH 4 + do dissolve Example of how we use solubility rules to explain the chemistry we see, a metathesis reaction: 2. Chapter 8 Physical Equilibria Rules: the physical reasons for why things dissolve ! multiply charged salts have a high heat of hydration and therefore are less soluble in water ! like dissolves like because of intermolecular force arguments so polar dissolves polar, non-polar dissolves non-polar Lets look an example of Like dissolves like what happens when you mix combinations of the four chemicals NaCl H 2 O ionic (polar) polar naphthalene (nonpolar) toluene (nonpolar) case 1: case 2: case 3: case 4: soluble...
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