1 CHAPTER 5 Read Chapter 5 Study examples and exercises

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  • Slide 1
  • 1 CHAPTER 5 Read Chapter 5 Study examples and exercises.
  • Slide 2
  • 2 Chapter 5 Outline Electrolytes NIEs 5 General Chemical Reactions Redox Acid/Bases Molarity Titration
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  • IONIC COMPOUNDS Compounds in Aqueous Solution aqueous solutions.Many reactions involve ionic compounds, especially reactions in water aqueous solutions. KMnO 4 in water K + (aq) + MnO 4 - (aq)
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  • 4 Aqueous Solutions How do we know ions are present in aqueous solutions? The solutions conduct electricity! ELECTROLYTES They are called ELECTROLYTES strong electrolytes. HCl, K 2 CrO 4, MgCl 2, and NaCl are strong electrolytes. They dissociate completely (or nearly so) into ions. K 2 CrO 4 (aq) ---> 2 K + (aq) + CrO 4 2- (aq)
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  • 5 NaCl dissolving in water Cl - Na + Negative O atom Positive H atom
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  • 6 Aqueous Solutions How do we know ions are present in aqueous solutions? The solutions conduct electricity! ELECTROLYTES They are called ELECTROLYTES strong electrolytes. HCl, MgCl 2, and NaCl are strong electrolytes. They dissociate completely (or nearly so) into ions.
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  • 7 Figure 5.2 Strong Electrolyte
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  • 8 Aqueous Solutions weak electrolyte. Acetic acid ionizes only to a small extent, so it is a weak electrolyte. HC 2 H 3 O 2 (aq)C 2 H 3 O 2 - (aq) + H + (aq)
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  • 9 Figure 5.3 Weak Electrolyte
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  • 10 Ionized acetic acid H+H+ Acetic acid Weak Electrolyte
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  • 11 Aqueous Solutions weak electrolyte. Acetic acid ionizes only to a small extent, so it is a weak electrolyte. CH 3 CO 2 H(aq) - CH 3 CO 2 - (aq) + H + (aq)
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  • 12 Aqueous Solutions nonelectrolytes. Some compounds dissolve in water but do not conduct electricity. They are called nonelectrolytes. Examples include: sugar ethanol ethylene glycol (in antifreeze)
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  • 13 Figure 5.3 b Nonelectrolyte
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  • 14 Nonelectrolyte Ethanol, C 2 H 5 OH
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  • 15 WATER SOLUBILITY OF IONIC COMPOUNDS INSOLUBLE. Not all ionic compounds dissolve in water. Some are INSOLUBLE. Figure 5.4 See Figure 5.4 As long as one ion from the list is present in a compound, the compound is water soluble.
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  • 16 See your Solubility Table
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  • 17 WATER SOLUBILITY OF IONIC COMPOUNDS Common minerals are often formed with anions that lead to insolubility: sulfidefluoride carbonateoxide Azurite, a copper carbonate Iron pyrite, a sulfide Orpiment, arsenic sulfide
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  • 18 An acid H + in water ACIDS strong Some strong acids are HClhydrochloric HNO 3 nitric HClO 4 perchloric H 2 SO 4 sulfuric HNO 3
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  • 19 An acid H + in water ACIDS HCl(aq) H + (aq) + Cl - (aq)
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  • 20 The Nature of Acids HCl H 2 O H 3 O + Cl - hydronium ion
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  • 21 Weak Acids WEAK ELECTROLYTES WEAK ACIDS = WEAK ELECTROLYTES HC 2 H 3 O 2 acetic acid H 2 CO 3 carbonic acid H 3 PO 4 phosphoric acid
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  • 22 ACIDS Nonmetal oxides can be acids CO 2 (aq) + H 2 O(l) H 2 CO 3 (aq) SO 3 (aq) + H 2 O(l) H 2 SO 4 (aq) and can come from burning coal and oil.
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  • 23 Base OH - in water BASES NaOH(aq) Na + (aq) + OH - (aq) NaOH is a strong base.
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  • 24 Ammonia, NH 3 An Important Base NH 3 (aq) + H 2 O(l) NH 4 + (aq) + OH - (aq)
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  • 25 Figure 5.11 Ammonia is a weak base
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  • 26 BASES Metal oxides are bases CaO(s)+ H 2 O(l) Ca(OH) 2 (aq) CaO in water. Indicator shows solution is basic.
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  • 27 Net Ionic Equations Mg(s) + 2 HCl(aq) H 2 (g) + MgCl 2 (aq) We really should write Mg(s) + 2 H + (aq) + 2 Cl - (aq) H 2 (g) + Mg 2+ (aq) + 2 Cl - (aq)
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  • 28 Ionic Equations SPECTATOR IONS The two Cl - ions are SPECTATOR IONS they do not participate. Mg(s) + 2 HCl(aq) H 2 (g) + MgCl 2 (aq) Mg(s) + 2 H + (aq) + 2 Cl - (aq)H 2 (g) + Mg 2+ (aq) + 2 Cl - (aq)
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  • 29 Net Ionic Equations Mg(s) + 2 HCl(aq) H 2 (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 in writing the NET IONIC EQUATION (NIE) Mg(s) + 2 H + (aq) H 2 (g) + Mg 2+ (aq)
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  • CHEMICAL REACTIONS IN WATER We will look at EXCHANGE REACTIONS The anions exchange places between cations. Pb(NO 3 ) 2 (aq) + 2 KI (aq) ----> PbI 2 (s) + 2 KNO 3 (aq) AX + BY AY X
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  • 31 Precipitation Reactions The driving force is the formation of an insoluble compound a precipitate. Pb(NO 3 ) 2 (aq) + 2 KI(aq) 2 KNO 3 (aq) + PbI 2 (s) Net ionic equation Pb 2+ (aq) + 2 I - (aq) PbI 2 (s)
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  • 32 Acid-Base Reactions The driving force is the formation of water.The driving force is the formation of water. NaOH(aq) + HCl(aq) NaCl(aq) + H 2 O(l) Net ionic equation OH - (aq) + H + (aq) H 2 O(l) OH - (aq) + H + (aq) H 2 O(l) This applies to ALL reactions of STRONG acids and bases.This applies to ALL reactions of STRONG acids and bases.
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  • 33 Acid-Base Reactions A-B reactions are sometimes called NEUTRALIZATIONS because the solution is neither acidic nor basic at the end.A-B reactions are sometimes called NEUTRALIZATIONS because the solution is neither acidic nor basic at the end. The other product of the A-B reaction is a SALT, MX.The other product of the A-B reaction is a SALT, MX. HX + MOH ---> MX + H 2 O HX + MOH ---> MX + H 2 O M n+ comes from the base & X n- comes from the acid. M n+ comes from the base & X n- comes from the acid. This is one way to make compounds! This is one way to make compounds!
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  • 34 Gas-Forming Reactions
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  • 35 Gas-Forming Reactions CaCO 3 (s) + H 2 SO 4 (aq) CaSO 4 (s) + H 2 CO 3 (aq) Carbonic acid is unstable and forms CO 2 & H 2 O H 2 CO 3 (aq) CO 2 (g) + water (Antacid tablet has citric acid + NaHCO 3 )
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  • 36 Oxidation-Reduction Reactions Fe 2 O 3 (s) + 2 Al(s) 2 Fe(s) + Al 2 O 3 (s) Thermite reaction
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  • 37 REDOX REACTIONS EXCHANGEAcid-BaseReactions EXCHANGEGas-FormingReactions EXCHANGE: Precipitation Reactions REACTIONS
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  • 38 REDOX REACTIONS Oxidation ( H, Mg, and Al ) 2 H 2 (g) + O 2 (g) 2 H 2 O(l) Mg(s) + 2 HCl(aq) MgCl 2 (aq) + H 2 (g) All corrosion reactions are oxidations. 2 Al(s) + 3 Cu 2+ (aq) 2 Al 3+ (aq) + 3 Cu(s) Reduction ( Fe +3 ) Fe 2 O 3 (s) + 2 Al(s) 2 Fe(s) + Al 2 O 3 (s)
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  • 39 But notice that in all reactions if something has been oxidized then something has also been reduced. But notice that in all reactions if something has been oxidized then something has also been reduced. Cu(s) + 2 Ag + (aq) Cu 2+ (aq) + 2 Ag(s) REDOX REACTIONS
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  • 40 Why Study Redox Reactions Manufacturing metals Fuels Corrosion Batteries
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  • 41 Redox reactions are characterized by ELECTRON TRANSFER between an electron donor and electron acceptor. Transfer leads to 1. Increase in oxidation number of some element = OXIDATION 2. Decrease in oxidation number of some element = REDUCTION REDOX REACTIONS
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  • 42 OXIDATION NUMBERS The electric charge an element APPEARS to have when electrons are counted by some arbitrary rules: The electric charge an element APPEARS to have when electrons are counted by some arbitrary rules: 1. Each atom in free element has ox. no. = 0 1. Each atom in free element has ox. no. = 0 Zn O 2 I 2 S 8 2. In simple ions, ox. no. = charge on ion 2. In simple ions, ox. no. = charge on ion -1 for Cl - +2 for Mg 2+ -1 for Cl - +2 for Mg 2+
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  • 43 OXIDATION NUMBERS 3. O has ox. no. = -2 3. O has ox. no. = -2 (except in peroxides: in H 2 O 2, O = -1) 4. Ox. no. of H = +1 4. Ox. no. of H = +1 (except when H is associated with a metal as in NaH where it is -1) 5. Algebraic sum of oxidation numbers 5. Algebraic sum of oxidation numbers = 0 for a compound = 0 for a compound = overall charge for an ion = overall charge for an ion
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  • 44 OXIDATION NUMBERS NH 3 N = ClO - Cl = H 3 PO 4 P = MnO 4 - Mn = Cr 2 O 7 2- Cr = C 3 H 8 C = Oxidation number of F in HF?
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  • 45 Recognizing a Redox Reaction Corrosion of aluminum 2 Al (s) + 3 Cu 2 + (aq) ---> 2 Al 3 + (aq) + 3 Cu (s) Al(s) --> Al 3+ (aq) + 3 e - Ox. no. of Al increases as e - are donated by the metal.Ox. no. of Al increases as e - are donated by the metal. Therefore, Al is OXIDIZED and is the REDUCING AGENT in this balanced half-reaction.Therefore, Al is OXIDIZED and is the REDUCING AGENT in this balanced half-reaction.
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  • 46 Recognizing a Redox Reaction Corrosion of aluminum 2Al (s) + 3Cu 2+ (aq) --> 2Al 3+ (aq) + 3Cu (s) Cu 2+ (aq) + 2 e - --> Cu(s) Ox. no. of Cu decreases as e - are accepted by the ion.Ox. no. of Cu decreases as e - are accepted by the ion. Therefore, Cu is REDUCED and is the