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Ch.13: Ions in Aqueous Solutions

Ch.13: Ions in Aqueous Solutions. Part 1. Ions separate from each other when ionic compounds dissolve in H 2 O. Dissociation = separation of ions when an ionic compound dissolves Assume 100% dissociation for soluble compounds Represented by an equation

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Ch.13: Ions in Aqueous Solutions

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  1. Ch.13: Ions in Aqueous Solutions Part 1

  2. Ions separate from each other when ionic compounds dissolve in H2O • Dissociation = separation of ions when an ionic compound dissolves • Assume 100% dissociation for soluble compounds • Represented by an equation NaCl (s)  Na+ (aq) + Cl-(aq) CaCl2(s)  Ca2+(aq) + 2Cl-(aq) Note: each equation is balanced for charge and number of atoms

  3. One formula unit of NaCL gives 2 ions • One formula unit of CaCl2 gives 3 ions this also means: NaCl (s) Na+(aq) + Cl-(aq) 1 mol 1 mol + 1 mol Sample problem: Write the equation for the dissociation of Al2(SO4)3 in water. How many moles of each ion are produced by dissolving 1 mol Al2(SO4)3 ? QUESTION: Why do we write the H2O above the arrow?

  4. Precipitation Reactions • Ionic compounds of very low solubility can be considered insoluble • We have general guidelines to help predict whether a compound made of a certain combination of ions is soluble

  5. Solubility Rules (p413 in book) • Na, K, NH4 = soluble • NO3, ClO3, CH3COO = Soluble • Cl- = soluble (except Ag, Mg, Pb) • SO42- = soluble (except Ba, Sr, Ca, Hg) • CO32-, PO43-, Si = Insoluble (except Na, K, NH4) • S2-, = insoluble (except Ca, Sr, Na, K, NH4) QUESTION: Is Ca3(PO4)2 soluble or insoluble in water? What will happen if 2 different soluble compounds are mixed? (NH4)2S (aq) + Cd(NO3)2 (aq)  2 NH4NO3 (?) + CdS (?)

  6. Net Ionic Equations • Rxns of ions in aqueous solutions are represented by net ionic equations • Includes only those compounds and ions that undergo chemical change in a rxn • Write FULL ionic equation with soluble ionic compounds shown as dissociated ions • Cancel out spectator ions • Write the net ionic equation

  7. Practice • Will a ppt form if solutions of K2SO4 and Ba(NO3)2 are combined? If so, write the net ionic equation. • Will a ppt form if solutions KNO3 and MgSO4 are combined? If so, write the net ionic equation. • Will a ppt form if solutions of barium chloride and sodium sulfate are combined? If so, write the net ionic equation.

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