General Chemistry I Fall 2007 Joann S. Monko Chemistry 9th ed. Raymond Chang IONIC COMPOUNDS in Aqueous Solution Reactions can involve ionic compounds reactions in water -- aqueous solutions. KMnO4 in water K+(aq) + MnO4-(aq) SOLVENT SOLUTE the component whose physical state is preserved when the solution forms the other solution component Or...The solvent is the medium in which another substance (the solute) is dissolved. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. An Ionic Compound, CuCl2, in Water Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Aqueous Solutions Are ions present in aqueous solutions? The solutions conduct electricity! Called ELECTROLYTES HCl, MgCl2, and NaCl are strong electrolytes. They dissociate completely into ions. Reactions use to show 100 % dissociation. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Aqueous Solutions Acetic acid ionizes only to a small extent = weak electrolyte. CH3CO2H(aq) CH3CO2-(aq) + H+(aq) Rxtns use equilibrium arrows to show less than 100% dissociation Rxtn favor products: Rxtn favors reactants: Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Aqueous Solutions Some compounds dissolve in water but do not conduct electricity. They are called nonelectrolytes. Examples include: sugar ethanol ethylene glycol Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Clicker Question Which is the strongest electrolyte? A. CH3COOH B. KCl C. C6H22O11 Water Solubility of Ionic Compounds If one ion from the "Soluble Compd." list is present in a compound, the compound is water soluble. Also see table 4.2 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Clicker Question Which of the following contain ALL soluble compounds? A. B. C. D. NaBr PbBr2 Zn(NO3)2 KOH NiBr2 Ca(OH)2 (NH4)2S AgCl Na3PO4 CuSO4 Li2O Mg3(PO4)2 Water Solubility of Ionic Compounds Common minerals are often formed with anions that lead to insolubility: sulfide fluoride carbonate oxide Azurite, a copper carbonate Iron pyrite, a sulfide Orpiment, arsenic sulfide Solubility is usually referenced as grams of solute that will dissolve in 100 g of water at a specific temperature. CuSO4 = 14.3 g / 100 g H2O @ 0 C Solubility increases as temperature increases. CuSO4 = 33.3 g / 100 g H2O @ 50 C Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Chemical Reactions in Water EXCHANGE REACTIONS Pb(NO3)2 (aq) + 2 KI (aq) ----> PbI2 (s) + 2 KNO3 (aq) AX + BY AY + BX The anions exchange places between cations. **Precipitation Reactions The "driving force" is the formation of an insoluble compound -- a precipitate. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. More Precipitation Reactions The reaction of silver nitrate and calcium chloride... __ AgNO3 (aq) + __ CaCl2 (aq) The reaction of sodium sulfate and barium bromide... __ Na2SO4 (aq) + __ BaBr2 (aq) The reaction of potassium carbonate and copper (II) iodide... __ K2CO3 (aq) + __ CuI2 (aq) The reaction of ammonium chloride and lithium hydroxide... __ NH4Cl (aq) + __ LiOH (aq) Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Clicker Question One of the products of the reaction is... CuCl2 (aq) + H2S (g) ___ + ___ A. CuS B. Cu2S C. CuS2 Clicker Question Predict the products & balance the equation: __ K3PO4 + __ Mg(NO3)2 __X + __Y The coefficient in front of the K3PO4 is... Net Ionic Equations -Only substances involved in the chemical change. Mg (s) + 2 HCl (aq) --> H2 (g) + MgCl2 (aq) We really should write Mg(s) + 2 H+ (aq) + 2 Cl-(aq) --> H2(g) + Mg2+(aq) + 2 Cl-(aq) The two Cl- ions are SPECTATOR IONS -- they do not participate. Could have used NO3-. Mg (s) + 2 HNO3- (aq) --> H2(g) + Mg(NO3)2 (aq) Mg (s) + 2 H+ (aq) + 2 NO3- (aq) --> H2(g) + Mg2+ (aq) + 2 NO3- (aq) Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Net Ionic Equations 1st Write the equation. 2nd Identify the states of the substances s, l, g, or aq 3rd Break substances into separate ions. Solids, Liquids and Gases do NOT get broken apart. 4th Cross out all ions that appear the same on both sides of the arrow...Spectator ions. Mg (s) + 2 HCl (aq) --> H2 (g) + MgCl2 (aq) Mg (s) + 2 H+ (aq) + 2 Cl- (aq) --> H2 (g) + Mg2+ (aq) + 2 Cl-(aq) We leave the spectator ions out -- Mg (s) + 2 H+ (aq) ---> H2 (g) + Mg2+ (aq) to give the NET Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. IONIC EQUATION Net Ionic Equations 2 AgNO3 (aq) + CaCl2 (aq) --> 2 AgCl (s) + Ca(NO3)2 (aq) Net: Na2SO4 (aq) + BaBr2 (aq) --> 2 NaBr (aq) + BaSO4 (s) Net: 2 HCl (aq) + Na2S (aq) --> H2S (g) + 2 NaCl (aq) Net: 2 HCl (aq) + SrCO3 (s) --> SrCl2 (aq) + H2O (l) + CO2 (g) Net: Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Gas-Forming Reactions This is primarily the chemistry of metal carbonates. MCO3 + acid ---> CO2 + salt +H20 CaCO3 (s) + 2 H+ (aq) ---> H2CO3 (aq) + Ca2+ (aq) H2CO3 (aq) ---> CO2 (g) + H2O (l) Other gases form from: metal sulfides, metal sulfites, & ammonium salts. H2S SO2 NH3 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. The Nature of Acids An acid -------> H+ in water HCl (aq) H+ (aq) + Cl- (aq) H2O + HCl H3O+ + Cl- Strong Acids dissociate 100%. HCl H2SO4 HClO4 HNO3 hydrochloric sulfuric perchloric nitric HCl Cl H2O H3O+ The Hydronium Ion Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. (Strong Electrolytes) Weak Acids WEAK ACIDS = weak electrolytes CH3CO2H acetic acid H2CO3 carbonic acid H3PO4 phosphoric acid HF hydrofluoric acid Acetic acid Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Acids Nonmetal oxides can be acids CO2 (aq) + H2O (l) ---> H2CO3 (aq) SO3 (aq) + H2O (l) ---> H2SO4 (aq) and can come from burning coal and oil. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Bases NaOH (aq) Base ---> OH- in water ---> Na+ (aq) + OH- (aq) NaOH is a strong base 100% ionization Strong electrolyte Metal oxides are bases CaO (s) + H2O (l) Ca(OH)2 (aq) CaO in water. Indicator shows solution is basic. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Ammonia, NH3 An Important Base Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Know the strong acids & bases! Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Acid-Base Reactions The driving force is the formation of water. NaOH (aq) + HCl (aq) ---> NaCl (aq) + H2O (l) Net ionic equation OH- (aq) + H+ (aq) H2O (l) For ALL rxtns of STRONG acids and bases. A-B rxtns A.K.A. NEUTRALIZATIONS -the solution is neither acidic nor basic at the end. Other product of the A-B rxtn is a SALT, MX. HX + MOH ---> MX + H2O Mn+ comes from base & Xn- comes from acid Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. The pH Scale pH = log (1/ [H+]) = - log [H+] In a neutral solution, [H+] = [OH-] = 1.00 x 10-7 M at 25 oC pH = - log [H+] = -log (1.00 x 10-7) = - (-7) = 7 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. +] [H and pH If the [H+] of soda is 1.6 x 10-3 M, the pH is ____? Because pH = - log [H+] then pH= - log (1.6 x 10-3) pH = - (-2.80) pH = 2.80 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. pH and [H+] If the pH of Coke is 3.12, it is ______. Because pH = - log [H+] then log [H+] = - pH Take antilog and get [H+] = 10-pH [H+] = 10-3.12 = 7.6 x 10-4 M Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Clicker Question Which statement is NOT Correct? A. pH = 1.89 is equal to [H+] = 1.29 x 10-2 M B. pH = 4.55 is equal to [H+] = 2.82 x 10-5 M C. pH = 7.38 is equal to [H+] = 4.17 x 10-8 M D. pH = 8.75 is equal to [H+] = 7.85 x 10-9 M E. pH= 11.05 is equal to [H+]= 8.91 x 10-12 M