9/13/2013 Ch 4 Chemical reactions Ch 4 Chemical Reactions Big Idea 3: Changes in matter involve the rearrangement and/or reorganization of atoms and/or the transfer of electrons Ch 4 Chemical Reactions Enduring understanding 3.A: Chemical changes are represented by a balanced chemical equation that identifies the ratios with which reactants react and products form. Essential knowledge 3.A.1: A chemical change may be represented by a molecular, ionic, or net ionic equation. 1 9/13/2013 Ch 4 Chemical Reactions Enduring understanding 3.B: Chemical reactions can be classified by considering what the reactants are, what the products are, or how they change from one into the other. Classes of chemical reactions include synthesis, decomposition, acid-base, and oxidation-reduction reactions. Ch 4 Chemical Reactions Sec 4.3 Precipitation Reactions Predict products of a metathesis reaction based upon the reactants Sec 4.1 Ionic Theory of Solutions and Solubility Rules Apply solubility rules to predict solubility of compounds in water Sec 4.2 Molecular and Ionic Equations Objectives Write chemical equations for a reaction as if all the substances were molecular Break apart molecular equations into a complete ionic equation based upon the definition of strong electrolyte Identify spectator ions in a complete ionic equation Evaluate a complete ionic equation, canceling out spectator ions to determine the net ionic equation of a chemical reaction 2 9/13/2013 Precipitation reactions Double replacement reaction When aqueous solutions of ionic compounds are reacted together a solid forms. A solid that forms from reacted solutions is a precipitate If you’re not a part of the solution, your part of the precipitate Precipitation reactions 3NaOH (aq) + FeCl3 (aq) →3NaCl (aq) + Fe(OH) 3 (s) is really 3Na+(aq)+3OH- (aq) +Fe+3(aq)+3Cl-(aq)→3Na+(aq)+3Cl-(aq)+ Fe(OH)3 (s) So all that really happens is 3OH- (aq) + Fe+3 (aq) → Fe(OH)3 (s) Precipitation reaction We can predict the products In a double displacement reaction, the anion and cation switch partners EXAMPLES AgNO3(aq) + KCl(aq) → Zn(NO3)2(aq) + BaCr2O7(aq) → CdCl2(aq) + Na2S(aq) → 3 9/13/2013 Precipitations Reactions Only happen if one of the products is insoluble or a pure substance (more on that later) Otherwise all the ions stay in solution- no reaction. Need to memorize the rules for solubility (pg 128 old book, pg 129 new book) Solubility Rules (aq) • • • Group IA and NH4+ ions are soluble Acetates and nitrates are soluble Most Group VIIA are soluble • except Ag+, Pb+2, Hg+2 and Hg2+2 • Most sulfates are soluble • except Pb+2, Ba+2, Hg+2, Sr+2, Ag+1and Ca+2 Solubility Rules (ppt) • Most carbonates are insoluble • except Group IA and Ammonium • Most phosphates are insoluble • except Group IA and Ammonium • Most sulfides are insoluble • except Group IA and Ammonium • Most Hydroxides are insoluble • except Group IA, Ca+2, Sr+2 , Ba+2 4 9/13/2013 Precipitation reaction Use Solubility Rules and Determine the States of the Products AgNO3(aq) + KCl(aq) → AgCl(?) + KNO3 (?) Zn(NO3)2(aq) + BaCr2O7(aq) →ZnCr2O7 (?)+Ba(NO3)2 (?) CdCl2(aq) + Na2S(aq) → CdS(?) + 2NaCl(?) What Really Happens in Solution? Look at each substance on an individual basis Determine if it’s a strong electrolyte or weak electrolyte Electrolytes and Nonelectrolytes Electrolyte: substance that dissolved in water produces a solution that conducts electricity Contains ions Nonelectrolyte: substance that dissolved in water produces a solution that does not conduct electricity Does not contain ions Copyright McGraw-Hill 2009 15 5 9/13/2013 Dissociation - ionic compounds separate into constituent ions when dissolved in solution Ionization - formation of ions by molecular compounds when dissolved Copyright McGraw-Hill 2009 16 Strong and weak electrolytes Strong Electrolyte: 100% dissociation All water soluble ionic compounds, strong acids and strong bases Weak electrolytes Exist mostly as the molecular form in solution Do not dissociate when dissolved in water Insoluble ionic compounds, Weak acids and weak bases Copyright McGraw-Hill 2009 17 Strong Electrolytes When dissolved in water, dissociate or ionize Soluble Ionic Compounds EX) NaNO3, MgCl2, Ca(C2H3O2)2 Strong Acids EX) HCl, HBr, HI Oxyacids with #O’s>#H’s by 2/more Strong Bases EX) All Hydroxides except those that are insoluble 6 9/13/2013 Weak Electrolytes Do not dissociate or ionize when dissolved in water Insoluble ionic compounds Weak Acids (must know these, memorize) AgCl, Ca(OH)2 HF, HCN, HC2H3O2 Oxyacids #O’s>#H’s by 1/less Weak Bases (must know these, memorize) NH3 For Every Double Displacement Reaction Three Types of Equations Molecular Equation- written as whole formulas, not the ions. K2CrO4(aq) + Ba(NO3)2(aq) → Complete Ionic equation show dissolved electrolytes as the ions and any precipitates formed. 2K+(aq)+CrO4-2(aq)+Ba+2(aq)+2NO3-(aq)→BaCrO4 (s)+2K+(aq)+2NO3- (aq) Spectator ions are those that don’t react. For Every Double Displacement Reaction Three Types of Equations Net Ionic equations show only those ions that react, not the spectator ions…they cancel out to make the net ionic equation +2 -2 Ba (aq) + CrO4 (aq) → BaCrO4(s) Write the molecular equation, the complete ionic equation and the net ionic equation for the reactions when these solutions are mixed. Example: iron (III) sulfate and potassium sulfide lead (II) nitrate and sulfuric acid. 7 9/13/2013 For Every Double Displacement Reaction Three Types of Equations Write the molecular equation, the complete ionic equation and the net ionic equation for the reactions when these solutions are mixed. Example: iron (III) sulfate and potassium sulfide lead (II) nitrate and sulfuric acid. Ch 4 Chemical Reactions Big Idea 3: Changes in matter involve the rearrangement and/or reorganization of atoms and/or the transfer of electrons Ch 4 Chemical Reactions Enduring understanding 3.B: Chemical reactions can be classified by considering what the reactants are, what the products are, or how they change from one into the other. Classes of chemical reactions include synthesis, decomposition, acid-base, and oxidation-reduction reactions. 8 9/13/2013 Chapter 4 Types of Chemical Reactions Writing Chemical Reactions Ch 4 Chemical Reactions Sec 4.5 Some Common Oxidation Reduction Reactions Identify the type of chemical reaction based on its characteristics Use the activity series of metals to predict the products of a single displacement reaction Predict products of a combination, combustion, displacement, or decomposition reaction based upon the reactants Types of Reactions Many chemical reactions have defining characteristics which allow them to be classified as to type. 9 9/13/2013 Types of Chemical Reactions The five types of chemical reactions in this unit are: Combination/Synthesis Decomposition Single Replacement Combustion Double Replacement Combination Reactions aka Synthesis Reactions Two or more substances combine to form one substance. The general form is A + X AX Example: Magnesium + chlorine magnesium chloride Mg + Cl2 MgCl2 Combination Reactions aka Synthesis Reactions Combination reactions may also be called composition or synthesis reactions. Some types of combination reactions: Combination of elements K + Cl2 One product will be formed 10 9/13/2013 Combination Reactions aka Synthesis Reactions K + Cl2 Write the ions: K+ Cl- Balance the charges: KCl Balance the equation: 2K + Cl2 2KCl Combination Reactions aka Synthesis Reactions Some types of combination reactions: Oxide + water Add algebraically and check valence charges Nonmetal oxide + water acid + H2O H2SO3 Metal oxide + water base BaO + H2O Ba(OH)2 SO2 Combination Reactions aka Synthesis Reactions Some types of combination reactions: Metal oxides + nonmetal oxides→ add algebraically (check valence charges) Na2O + CO2 Na2CO3 CaO + SO2 CaSO3 11 9/13/2013 Decomposition Reactions One substance (Binary Compound) reacts to form two or more substances. The general form is AX A + X When forming an element as a product, check if diatomic Example: Water can be decomposed by electrolysis. 2H2O 2H2 + O2 Decomposition Reactions Types of Decomposition Reactions: heated, some carbonates break down to form a metal oxide and carbon dioxide. CaCO3 CaO + CO2 H2CO3 H2O + CO2 When Decomposition Reactions Types of decomposition reactions: Some metal hydroxides decompose into metal oxides and water when heated. Ca(OH)2 CaO + H2O Note that this is the reverse of a similar combination reaction. 12 9/13/2013 Decomposition Reactions Types of decomposition reactions: Metal chlorates decompose into metal chlorides and oxygen when heated. 2KClO3 2KCl + 3O2 Zn(ClO3)2 ZnCl2 + 3O2 Some of these reactions are used in explosives. Decomposition Reactions Some substances can easily decompose: Ammonium hydroxide is actually ammonia gas dissolved in water. (add algebraically) NH4OH NH3 + H2O Ternary acids decompose into water and an oxide. (add algebraically) H2CO3 H2O + CO2 Decomposition Reactions Some decomposition reactions are difficult to predict. 13 9/13/2013 Single Replacement Reactions A metal element will replace a metal ion in a binary compound. The general form is A + BX AX + B First, check the Activity Series Is element A stronger than element B? Single Replacement Reactions First, check the Activity Series Is element A stronger than element B? Single Replacement Reactions A nonmetal will replace a nonmetal ion in a binary compound. The general form is Y + BX BY + X Use the Activity Series for Nonmetals…The Halogen Family on the Periodic Table 14 9/13/2013 Single Replacement Reactions Examples: Ni + AgNO3 Nickel replaces the metallic ion Ag+. The silver becomes free silver and the nickel becomes the nickel(II) ion. Ni + AgNO3 Ag + Ni(NO3)2 Balance the equation: Ni + 2AgNO3 2Ag + Ni(NO3)2 Single Replacement Reactions Not all single replacement reactions that can be written actually happen. The metal must be more active than the metal ion. Aluminum is more active than iron in Al + Fe2O3→ Thermite Reaction http://www.youtube.com/watch?v=M3Zko NF2ybg 15 9/13/2013 Thermite Reaction Example of a Single replacement Reaction Al + Fe2O3 Aluminum will replace iron(III) as was seen in the video. Iron(III) becomes Fe and aluminum metal becomes Al3+. 2Al + Fe2O3 2Fe + Al2O3 Single Replacement Reactions An active nonmetal can replace a less active nonmetal. The halogen (F2, Cl2, Br2, I2) reactions are good examples. F2 is the most active and I2 is the least. Cl2 +2 NaI 2 NaCl + I2 Combustion Reaction When an element is burned, it combines with oxygen, a combustion reaction results. The combustion reaction may look similar to a combination reaction, but the difference here is oxygen is ALWAYS A REACTANT 2Mg + O2 2MgO. 16 9/13/2013 Combustion Reaction Methane, CH4, is natural gas. It is a “hydrocarbon” When hydrocarbon compounds are burned in oxygen, the products are water and carbon dioxide. CH4 + O2 CO2 + H2O CH4 + 2O2 CO2 + 2H2O Combustion Reactions Combustion reactions involve light and heat energy released. Natural gas, propane, gasoline, etc. are burned to produce heat energy. Most of these organic reactions (hydrocarbon compounds) produce water and carbon dioxide. Classify each of the following as to type: H2 + Cl2 2HCl Ca + 2H2O Ca(OH)2 + H2 Single replacement 2CO + O2 2CO2 Combination Combination and combustion 2KClO3 2KCl + 3O2 Decomposition 17 9/13/2013 Double Displacement Reactions 2 Ionic Compounds Each has a cation (+ ion) and an anion (- ion) Cations(+ ion) and Anions(- ion) Exchange partners Must always form a pure substance in the form of a solid, liquid or gas (s), (l), (g) [(s) known as a precipitate] Double Displacement Reactions 2 “special types” Acid base reaction (aka Neutralization Reaction) Precipitation reaction Ch 4 Chemical Reactions Big Idea 3: Changes in matter involve the rearrangement and/or reorganization of atoms and/or the transfer of electrons 18 9/13/2013 Ch 4 Chemical Reactions Enduring understanding 3.B: Chemical reactions can be classified by considering what the reactants are, what the products are, or how they change from one into the other. Classes of chemical reactions include synthesis, decomposition, acid-base, and oxidation-reduction reactions. Essential knowledge 3.B.2: In a neutralization reaction, protons are transferred from an acid to a base. Acid Base Reactions special double replacement reaction Acid-Base For our purposes an acid is a proton donor. a base is a proton acceptor usually OHWhat is the net ionic equation for the reaction of HCl(aq) and KOH(aq)? Acid + Base → salt + water H+ + OH- → H2O Acid - Base Reactions special double replacement reaction Often called a neutralization reaction Because the acid neutralizes the base. Often titrate to determine concentrations. Solution of known concentration (titrant), is added to the unknown (analyte), until the equivalence point is reached where enough titrant has been added to neutralize it. 19 9/13/2013 Acid-Base Reaction special double replacement reaction HCl is mixed with Ba(OH)2 . What is the neutralization reaction? Why is it called a neutralization reaction? Ch 4 Oxidation Reduction Reactions Ch 4 Chemical Reactions Big Idea 3: Changes in matter involve the rearrangement and/or reorganization of atoms and/or the transfer of electrons 20 9/13/2013 Ch 4 Chemical Reactions Enduring understanding 3.B: Chemical reactions can be classified by considering what the reactants are, what the products are, or how they change from one into the other. Classes of chemical reactions include synthesis, decomposition, acid-base, and oxidation-reduction reactions. Essential knowledge 3.B.3: In oxidation-reduction (redox) reactions, there is a net transfer of electrons. The species that loses electrons is oxidized, and the species that gains electrons is reduced. Sec 4.5 Oxidation Reduction Reactions Objectives Define oxidation–reduction reaction. Learn the oxidation-number rules. Assign oxidation numbers Write the half-reactions of an oxidation– reduction reaction. Determine the species undergoing oxidation and reduction. Types of Chemical Reactions Oxidation-Reduction called Redox Substances are formed through the transfer of electrons. An Oxidation-reduction reaction involves the transfer of electrons. We need a way of keeping track. 21 9/13/2013 Types of Chemical Reactions The four types of chemical reactions in this unit can be classified as redox are: Combination/Synthesis Decomposition Single Replacement Combustion Double Replacement Oxidation States A way of keeping track of the electrons. Not necessarily true of what is in nature, but it works. need the rules for assigning (memorize). Oxidation states • The oxidation state of elements in their standard states is zero. • Oxidation state for monoatomic ions are the same as their charge. • Oxygen is assigned an oxidation state of -2 in its covalent compounds except as a peroxide. • In compounds with nonmetals hydrogen is assigned the oxidation state +1. • In its compounds fluorine is always –1. • The sum of the oxidation states must be zero in compounds or equal the charge of the ion. 22 9/13/2013 Oxidation States Assign the oxidation states to each element in the following. CO2 NO3H2SO4 Fe2O3 Fe3O4 Oxidation-Reduction Reactions Transfer electrons, so the oxidation states change. Na + 2Cl2 → 2NaCl CH4 + 2O2 → CO2 + 2H2O Oxidation is the loss of electrons. Reduction is the gain of electrons. OIL RIG LEO GER Oxidation-Reduction Reactions Oxidation means an increase in oxidation state - lose electrons. Reduction means a decrease in oxidation state - gain electrons. The substance that is oxidized is called the reducing agent. The substance that is reduced is called the oxidizing agent. 23 9/13/2013 Agents Oxidizing agent gets reduced. Gains electrons. More negative oxidation state. Reducing agent gets oxidized. Loses electrons. More positive oxidation state. EXAMPLE PROBLEM Directions: Identify the Oxidizing agent, Reducing agent, Substance oxidized, Substance reduced Fe (s) + O2(g) → Fe2O3(s) Fe2O3(s)+ 3 CO(g) → 2 Fe(l) + 3 CO2(g) SO32- + H+ + MnO4- → SO42- + H2O + Mn2+ 24
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