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Ch5_A_Ions - IONIC COMPOUNDS Compounds in Aqueous Solution...

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Unformatted text preview: IONIC COMPOUNDS Compounds in Aqueous Solution Many reactions involve ionic compounds, especially reactions in water — aqueous aqueous Aqueous Solutions How do we know ions are present in aqueous solutions? The solutions conduct electricity! They are called ELECTROLYTES ELECTROLYTES HCl, KMnO4, MgCl 2, and NaCl are strong HCl, strong electrolytes. They dissociate completely They (or nearly so) into ions. KMnO4(aq) ---> K+(aq) + MnO4-(aq) aq) aq) aq) Positive H atom ClNa+ Negative O atom solutions. KMnO4 in water in K+(aq) + MnO4-(aq) aq) aq) NaCl dissolving in water Aqueous Solutions How do we know ions are present in aqueous solutions? The solutions conduct electricity! They are called ELECTROLYTES ELECTROLYTES HCl, MgCl 2, and NaCl are strong HCl, strong electrolytes. They dissociate completely They (or nearly so) into ions. Aqueous Solutions Acetic acid ionizes only to a small extent, so it is a weak electrolyte. weak Aqueous Solutions Acetic acid ionizes only to a small extent, so it is a weak electrolyte. weak CH3CO2H(aq) H(aq) ---> CH 3CO2-(aq) + H+(aq) aq) aq) CH3CO2H(aq) H(aq) ---> CH 3CO2-(aq) + H+(aq) aq) aq) + Page 1 Acetic acid — Weak Electrolyte Ionized acetic acid Aqueous Solutions Some compounds dissolve in water but do not conduct electricity. They are called nonelectrolytes. nonelectrolytes. Examples include: sugar ethanol ethylene glycol (in antifreeze) Nonelectrolyte— Ethanol, C 2H5OH H+ WATER SOLUBILITY OF IONIC COMPOUNDS Not all ionic compounds dissolve in water. Some are INSOLUBLE . INSOLUBLE See Screen 4.6 and Figure 5.4 WATER SOLUBILITY OF IONIC COMPOUNDS Common minerals are often formed with anions that lead to insolubility: sulfide fluoride carbonate oxide ACIDS ACIDS An acid -------> H + in water An acid -------> H + iin water n As long as one ion from the list is present in a compound, the compound is water soluble. Iron pyrite, a sulfide Azurite, a copper carbonate Orpiment, arsenic sulfide Some strong acids are strong acids HCl hydrochloric H2SO4 sulfuric HClO 4 perchloric HNO3 nitric HNO3 Page 2 ACIDS ACIDS An acid -------> H + in water An acid -------> H + iin water n HCl(aq) ---> H+(aq) + Cl-(aq) HCl( aq) aq) aq) The The Nature of Nature of Water Water HCl Cl- Weak Acids Weak Acids WEAK ACIDS = weak electrolytes CH3CO2H acetic acid H2CO3 carbonic acid H3PO4 phosphoric acid H2O hydronium ion H3O+ The The Nature Nature of of Acids Acids ACIDS ACIDS Nonmetal oxides can be acids CO2(aq) + H2O(liq) aq) O(liq) ---> H 2CO3(aq) aq) SO3(aq) + H2O(liq) aq) O(liq) ---> H 2SO4(aq) aq) and can come from burning coal and oil. BASES see Screen 4.8 and Table 4.1 see Screen 4.8 and Table 4.1 Ammonia, NH3 An Important Base NH3(aq) + H 2O(liq) aq) O(liq) ---> NH 4+( aq) + OH -(aq) aq) aq) Base ---> OH -- in water Base ---> OH iin water n NaOH(aq) NaOH( aq) ---> Na+(aq) + OH-(aq) aq) aq) NaOH is a strong base Page 3 BASES BASES Metal oxides are bases CaO(s) + H 2O(liq) CaO(s) O(liq) --> Ca(OH) 2(aq) aq) Net Ionic Equations Mg(s) + 2 HCl(aq) --> H2(g) + MgCl 2(aq) HCl(aq) aq) We really should write Mg(s) + 2 H +(aq) + 2 Cl-(aq) ---> aq) aq) H2(g) + Mg 2+(aq) + 2 Cl-(aq) aq) aq) Net Ionic Equations Net Ionic Equations Mg(s) + 2 HCl(aq) HCl(aq) --> H2(g) + MgCl 2(aq) aq) Mg(s) + 2 H +(aq) + 2 Cl-(aq) aq) aq) ---> H 2(g) + Mg 2+(aq) + 2 Cl-(aq) aq) aq) We leave the spectator ions out — Mg(s) + 2 H+(aq) ---> H 2(g) + Mg2+(aq) aq) aq) to give the NET NET CaO in water. Indicator shows solution is basic. The two Cl- ions are SPECTATOR IONS — ions SPECTATOR they do not participate. Could have used NO 3-. IONIC EQUATION Page 4 ...
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