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