c101-lecture-5 - 2/9/11 Precipitation Reactions...

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2/9/11 1 Precipitation Reactions A precipitate forms when a chemical reaction of solutions produces a solid product. A salt is an ionic compound. Ionic compounds result when metals bind with non-metals (elements from left side of Periodic Table with elements from right side of Periodic Table) or with the common anions (NO 3 - , SO 4 2- , etc.). Precipitation Reactions Salts may be either soluble or insoluble in water. When soluble salts dissolve in solution, they produce cations and anions in the aqueous phase. Precipitation Reactions Solubility Rules Salts containing NH 4 + or alkali metal cations (Li, Na, K, Rb, Cs, Fr) are soluble. Salts containing the following anions are soluble with the exceptions noted: NO 3 - : no exceptions ClO 4 - : no exceptions HSO 4 - : no exceptions CH 3 CO 2 - : no exceptions Precipitation Reactions Solubility Rules (con t.) Salts containing the following anions are soluble with the exceptions noted: Cl - : AgCl, Hg 2 Cl 2 , PbCl 2 Br - : AgBr, Hg 2 Br 2 , PbBr 2 I - : AgI, Hg 2 I 2 , PbI 2 SO 4 2- : Hg 2 SO 4 , PbSO 4 , CaSO 4 , SrSO 4 , BaSO 4 Precipitation Reactions Solubility Rules (con t.) Ca(OH) 2 , Sr(OH) 2 , and Ba(OH) 2 and Group 1 (Li, Na, K, etc.) hydroxides are soluble—all other hydroxide are insoluble Precipitation Reactions Does a precipitate form when solutions of NaCl (aq) and AgNO 3 (aq) are mixed? 1. What does the mixture look like initially? Na + (aq) + Cl - (aq) + Ag + (aq) + NO 3 - (aq)
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2/9/11 2 Precipitation Reactions 2. Form possible cation/anion combinations—do any of the resulting species form a precipitate? Ions in solution: Na + (aq), Ag + (aq), Cl - (aq), NO 3 - (aq) NaCl(s)? No—all salts with Na + are soluble AgNO 3 (s)? No—all salts with NO 3 - are soluble NaNO 3 (s)? No—Na + and NO 3 - solubility rules AgCl(s)? Yes—because this is one of the exceptions to the Cl - family of soluble salts The net ionic equation involves only those ions participating in the chemical reaction: Na + (aq) + Cl - (aq) + Ag + (aq) + NO 3 - (aq) AgCl(s) + Na + (aq) + NO 3 - (aq) net ionic eqn: Ag + (aq) + Cl - (aq) AgCl(s) Na + (aq) and NO 3 - (aq) are called spectator ions because they do not participate in the formation of products—their role is to balance the total electrical charge of the solution. Spectator ions are not included in the net ionic equation. Precipitation Reactions Aqueous Solutions A solution is composed of two parts: the solute and the solvent. – The solute is the minor component of the solution. – The solvent is the major component of the solution and is the liquid into which the solute is added. Aqueous solutions are those in which water acts as the solvent. Concentration Units
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This note was uploaded on 03/05/2011 for the course CHEM 101 taught by Professor Scottnickolaisen during the Spring '11 term at California State University Los Angeles .

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c101-lecture-5 - 2/9/11 Precipitation Reactions...

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