13+Solubility+equilibria - AP Chemistry Solubility Equilibrium SOLUBILITY EQUILIBRIA(The Solubiliy-Product Constant Ksp Weve got good news and weve got

13+Solubility+equilibria - AP Chemistry Solubility...

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AP* Chemistry Solubility Equilibrium *AP is a registered trademark of the College Board, which was not involved in the production of, and does not endorse, this product.© 2008 by René McCormick. All rights reserved SOLUBILITY EQUILIBRIA (The Solubiliy-Product Constant, K sp ) We’ve got good news and we’ve got bad news… The good news: Solubility equilibrium is really simple. The bad news: You know all those solubility rules that state a substance is insoluble ? They are actually a bit soluble after all. Only the future attorneys among you read the fine print. Soluble is often defined as greater than 3 grams dissolving in 100 mL of water. So, there is a lot of wiggle room for solubility up to 3 grams! This type of equilibria deals with that wiggle room. If you can actually see that a salt is insoluble, then the solution is actually saturated. Saturated solutions of salts present yet another type of chemical equilibria. ¾ Slightly soluble salts establish a dynamic equilibrium with the hydrated cations and anions in solution. When the solid is first added to water, no ions are initially present. As dissolution proceeds, the concentration of ions increases until equilibrium is established. This occurs when the solution is saturated. The equilibrium constant, the K sp , is no more than the product of the ions in solution. (Remember, solids do not appear in equilibrium expressions.) For a saturated solution of AgCl, the equation would be: AgCl( s ) R Ag + ( aq ) + Cl ( aq ) The solubility product expression would be: K sp = [Ag + ][Cl ] The AgCl( s ) does not appear in the equilibrium expression since solids are left out. Why? The concentration of the solid remains relatively constant. A table of K sp values follows on the next page.
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Solubility Equilibria 2 Write the K sp expression for each of the following reactions and find its value in the table above. CaF 2 ( s ) R Ca +2 + 2 F K sp = Ag 2 SO 4 ( s ) R 2 Ag + + SO 4 2 K sp = Bi 2 S 3 ( s ) R 2 Bi +3 + 3 S 2 K sp = DETERMINING K sp FROM EXPERIMENTAL MEASUREMENTS ¾ In practice, K sp values are determined by careful laboratory measurements using various spectroscopic methods.
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