CHEM 113 1st Edition Lecture 27Outline of Last Lecture- Acid-Base Indicators- Acid-Base TitrationsOutline of Current Lecture- Amino Acids- Slightly soluble compounds- Ion-product expression- Metal sulfidesCurrent Lecture- Amino Acids as Polyprotic Acidso An amino acid contains a weak base (NH2) and a weak acid (COOH) in the same moleculeo Both groups are protonated a low pH and the amino acid behave like a polyproticacid.o So in conclusion, amino acids are weak acids!- Equilibria of Slightly Soluble Ionic Compoundso Any “insoluble” ionic compound is actually slightly soluble in aqueous solution. Only a small amount of the compound will dissolve, but this small amountwill dissociate completely.o For a slightly soluble ionic compound in water, equilibrium exists between solid solute and aqueous ions. For example, for a saturated solution of lead(2) fluoride we have- For this system the reaction quotient can be written as These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- If we multiply the constant concentration of the solid by Qc we get a relationship called the ion-product expression, Qsp- Ion-product expressiono Qsp is called the ion-product expression for a slightly soluble compoundo When the solution is saturated, the system is at equilibrium and Qsp=Ksp Ksp: the solubility product constant The Ksp value of a salt indicates how far the dissolution proceeds at equilibrium, which is saturation Notice this is very similar to previous K and Q relationships we have looked at.- Metal Sulfideso Metal sulfides behave differently from most other slightly soluble ionic compounds, since S2- ion is strongly basic Meaning the sulfide ion completely reacts with water to form the ions HS-and OH-o The dissolution of a metal sulfide is looked at as a two step process For example, solubility product constant for manganese (2) sulfide can be found through the following process- Sample Problem 19.5 & 19.6 utilizes the ideas in these
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