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1 Chapter Four Chemical Reactions in Aqueous Solutions Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four Today… • Turn in: • Nothing • Our Plan: • Notes – Synthesis & Decomposition • Begin Worksheet #1 • Homework (Write in Planner): • WS#1 Due Wednesday Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter One Unit 1 Test Results A B C D F 1 6 6 3 0 Average 78.47% High Score 96% Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter One 4 Quick Review • How do we know a chemical reaction has occurred? What do we observe? Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 5 Evidence of a Chemical Rxn 1. 2. 3. 4. Color Change Precipitate (solid) forms Gas Evolved Heat/Light Given Off – Endothermic – heat absorbed (gets cold) – Exothermic – heat released (gets hot) • More about this in Unit 5 - Thermodynamics Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 6 Review of Basics • When writing out a balanced equation, it is necessary to indicate what state the substance is in (s, l, g, or aq). • For elements, you can look at the PT to determine their standard state. – Examples: • Mercury • Fluorine • Iron Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 7 Review of Basics • There are 7 diatomic elements. • They are only diatomic when they are alone. They are all gases, except Br2, which is a liquid, as indicated on the PT. • Remember the Super 7? –H2, N2, O2, F2, Cl2, Br2, I2 Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 8 Review of Basics • Soluble means the substance dissolves in solution (water). – Label soluble substances aqueous (aq) • Insoluble means the substance does not dissolve in solution. – Label insoluble substances solid (s) • To determine if a substance is soluble or insoluble, use a solubility table. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 9 Solubility Chart Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 10 Other Basic Tips • Acids and bases are aqueous • Water is almost always a liquid • Write water as HOH when it is a reactant • Some common gases that aren’t diatomic are CO2, CO, SO3, SO2, H2S, and NH3 Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 11 Other Basic Tips • If a reaction indicates that a catalyst was present, it is not part of the actual reaction. Instead, you write the catalyst above the arrow. • Catalysts are not used up in the reaction. They are just there to speed it up. • If a reaction is heated, you draw a triangle above the arrow. Heat is used as a catalyst. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 12 Synthesis Reactions • Occur when two or more reactants combine to form a single product. –In Chem 1 we called this type “Dating” • There are several common types of synthesis reactions. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 13 Synthesis Reactions Type 1: A metal combines with a nonmetal to form a binary salt. Example: A piece of lithium metal is dropped into a container of nitrogen gas. 6Li (s) + N2 (g) → 2Li3N (aq) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 14 Synthesis Reactions Type 2: Metallic oxides and water form bases (metallic hydroxides). Example: Solid sodium oxide is added to water Na2O (s) + HOH (l) → 2NaOH (aq) Example: Solid magnesium oxide is added to water. MgO (s) + HOH (l) → Mg(OH)2 (aq) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 15 Synthesis Reactions Type 3: Nonmetallic oxides and water form acids. The nonmetal retains its oxidation number. Example: Carbon dioxide is bubbled in water. CO2 (g) + H2O (l) → H2CO3 (aq) Example: Dinitrogen pentoxide is bubbled in water. N2O5 (g) + H2O (l) → 2HNO3 (aq) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 16 Synthesis Reactions Type 4: Metallic oxides and nonmetallic oxides form salts. Example: Solid sodium oxide is added to carbon dioxide. Na2O (s) + CO2 (g) → Na2CO3 (aq) Example: Solid calcium oxide is added to sulfur trioxide. CaO (s) + SO3 (g) → CaSO4 (aq) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 17 Try It Out 1 • Solid barium oxide is added to distilled water (p. 142) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 18 Try It Out 2 • Sulfur trioxide gas is added to excess water (p. 146) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 19 Decomposition Reactions • Occur when a single reactant is broken down into two or more products. – In Chem 1 we called this “The Break Up” • There are several common types of decomposition reactions. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 20 Decomposition Reactions Type 1: Metallic carbonates decompose into metallic oxides and carbon dioxide Example: A sample of magnesium carbonate is heated. MgCO3 (s) → MgO (s) + CO2 (g) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 21 Decomposition Reactions Type 2: Metallic chlorates decompose into metallic chlorides and oxygen. Example: A sample of magnesium chlorate is heated. Mg(ClO3)2 (aq) → MgCl2 (aq) + 3O2 (g) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 22 Decomposition Reactions Type 3: Ammonium carbonate decomposes into ammonia, water, and carbon dioxide. Example: A sample of ammonium carbonate is heated. (NH4)2CO3 (aq)→ 2NH3 (g) + H2O (l) + CO2 (g) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 23 Decomposition Reactions Type 4: Sulfurous acid decomposes into sulfur dioxide and water. Example: A sample of ammonium carbonate is heated. H2SO3 (aq) → H2O (l) + SO2 (g) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 24 Decomposition Reactions Type 5: Carbonic acid decomposes into carbon dioxide and water. Example: A sample of carbonic acid is heated. H2CO3 (aq) → H2O (l) + CO2 (g) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 25 Decomposition Reactions Type 6: A binary compound may break down to produce two elements. Example: Molten sodium chloride is electrolyzed. 2NaCl (l) → 2Na (s) + Cl2 (g) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 26 Decomposition Reactions Type 7: Hydrogen peroxide decomposes into water and oxygen. Example: 2H2O2 (aq) → 2H2O (l) + O2 (g) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 27 Decomposition Reactions Type 8: Ammonium hydroxide decomposes into ammonia and water. Example: NH4OH (aq) → NH3 (g) + HOH (l) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 28 Try It Out 1 • Solid calcium chlorate is heated in the presence of a magnesium dioxide catalyst Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 29 Try It Out 2 • A sample of lithium carbonate is heated strongly Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 30 STOP • Complete Worksheet #1 by next class. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four Today… • Turn in: • Get Out WS#1 • Our Plan: • Questions on WS#1 • Quick Review • Notes – Single & Double Replacement • Begin WS#2 • Homework (Write in Planner): • WS#2 Due Friday Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter One 32 Quick Review • Write formulas for the reactants and predicted products for the chemical reactions that follow: 1. Solid calcium carbonate is strongly heated in a test tube. 2. Solid lithium chlorate is heated in the presence of a manganese dioxide catalyst. 3. Excess chlorine gas is passed over hot iron filings. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter One 33 Single Replacement • Reactions that involve an element replacing one part of a compound. • The products include the displaced element and a new compound. – In Chem 1 we called this “Cheating” • An element can only replace another element that is less active than itself. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 34 Single Replacement General Activity Series for Metals: Most Active Li Ca Na Mg Al Zn Fe Pb H2 Cu Ag Pt Au Least Active Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 35 Single Replacement General Activity Series for Nonmetals: Most Active F2 Cl2 Br2 I2 Least Active Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 36 Remember the Trend? • Or you can just look at the Periodic Table – The most reactive metals are on the bottom left (Francium) – The most reactive nonmetals are on the top right (Fluorine) – Hydrogen is the tricky one. – Use the pink sheet for electronegativity potentials otherwise. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 37 For metals, the more negative the reduction potential, the more reactive. For nonmetals, the more positive the reduction potential, the more reactive. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 38 Single Replacement Type 1: Active metals replace less active metals from their compounds in aqueous solution. Example: Magnesium turnings are added to a solution of iron (III) chloride. 3Mg (s) + 2FeCl3 (aq)→ 2Fe (s) + 3MgCl2 (aq) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 39 Single Replacement Type 2: Active metals replace hydrogen in water. Example: Sodium is added to water. 2Na (s) + 2HOH (l)→ 2NaOH (aq) + H2 (g) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 40 Single Replacement Type 3: Active metals replace hydrogen in acids. Example: Lithium is added to hydrochloric acid. 2Li (s) + 2HCl (aq) → 2LiCl (aq) + H2 (g) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 41 Single Replacement Type 4: Active nonmetals replace less active nonmetals from their compounds in aqueous solution. Example: Chlorine gas is bubbled into a solution of potassium iodide. Cl2 (g) + 2KI (aq) → I2 (g) + 2KCl (aq) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 42 Single Replacement Type 5: If a less reactive element is combined with a more reactive element in compound form, their will be no resulting reaction. Example: Chlorine gas is bubbled into a solution of potassium iodide. Cl2 (g) + KF (aq) → No Reaction Example: Zinc is added to a solution of sodium chloride. Zn (s) + NaCl (aq) → No Reaction Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 43 Try It Out 1 • A piece of aluminum metal is added to a solution of gold nitrate. (p. 146) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 44 Try It Out 2 • Liquid bromine is shaken with a potassium iodide solution. (p. 152) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 45 Try It Out 3 • Small chunks of potassium are added to water. (p. 164) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 46 Try It Out 4 • Small strips of platinum are placed in hydrochloric acid. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 47 Double Replacement • Reactions between two compounds in aqueous solution where the cations and anions appear to “switch partners”. AX + BY → AY + BX • In Chem 1 we called this “Swapping” Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 48 Double Replacement • All double replacement reactions (aka metathesis) must have a “driving force” or reason why the reaction will occur or “go to completion”. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 49 Double Replacement • “Driving Force” for reactions: 1. Formation of a precipitate 2. Formation of a gas 3. Formation of primarily molecular species (nonelectrolytes, water, weak acids) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 50 Double Replacement • If one of these “driving forces” is NOT present, then the reaction does not go to completion. • This type of reaction is indicated by a double arrow Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 51 Reactions that Form Precipitates • There are limits to the amount of a solute that will dissolve in a given amount of water. • If the maximum concentration of solute is less than about 0.01 M, we refer to the solute as insoluble in water. • When a chemical reaction forms such a solute, the insoluble solute comes out of solution and is called a precipitate. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 52 Silver Iodide Precipitation A solution containing silver ions and nitrate ions, when added to … … a precipitate of silver iodide. … a solution containing potassium ions and iodide ions, forms … Prentice Hall © 2005 What is the net ionic equation for the reaction that has occurred here? (Hint: what species actually reacted?) General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 53 Double Replacement (Precipitate) • In order to predict double replacement reactions yielding precipitates, one must memorize the solubility rules. • I will let you use a solubility chart on your test! Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 54 Solubility Rules Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 55 Example 1 • Predict and balance the following double replacement reactions based on the solubility of the products. Use the abbreviations (aq) and (s) for the reactant and products. All reactants are aqueous. 1. Solutions of manganese (II) sulfate and ammonium sulfide are mixed. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 56 Example 2 2. Solutions of sodium iodide and lead (II) nitrate are combined. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 57 Try it Out 1 • Solutions of sodium carbonate and iron (III) nitrate combine. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 58 Try it Out 2 • Solutions of lead (II) acetate and calcium chloride are combined. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 59 Double Replacement (Gas) • Common Gases formed: H2S, CO2, SO2, NH3 • Reactions that produce three of the gases (CO2, SO2, and NH3) involve the initial formation of a substance that breaks down to give the gas and HOH. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 60 Double Replacement (Gas) Common Gases H2S CO2 SO2 NH3 Prentice Hall © 2005 Any sulfide (salt of S2-) plus any acid form H2S (g) and a salt. Any carbonate (salt of CO32-) plus any acid form CO2 (g), HOH, and a salt Any sulfite (salt of SO32-) plus any acid form SO2 (g), HOH, and a salt. Any ammonium salt (salt of NH4+) plus any soluble strong hydroxide react upon heating to form NH3 (g), HOH, and a salt. General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 61 Double Replacement (Gas) • Example 1: The reaction of Na2SO3 and HCl produces H2SO3: Na2SO3 (aq) + 2HCl (aq) → H2SO3 (aq) + 2NaCl (aq) • Bubbling is observed in this reaction because the H2SO3 (sulfurous acid) is unstable and immediately decomposes to give HOH and SO2 gas: H2SO3 (aq) → HOH (l) + SO2 (g) • The molecular equation for the overall or complete reaction, therefore, is: Na2SO3 (aq) + 2HCl (aq) → HOH (l) + SO2 (g) + 2NaCl (aq) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 62 Double Replacement (Gas) • Example 2: A typical reaction of a carbonate and an acid is: K2CO3 (aq) + 2HNO3 (aq) → HOH (l) + CO2 (g) + 2KNO3 (aq) • Bubbling is also observed in this reaction. Theoretically H2CO3, carbonic acid, is formed, but the acid is unstable and immediately decomposes to form carbon dioxide gas and water according to the following equation: H2CO3 (aq) → HOH (l) + CO2 (g) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 63 Double Replacement (Gas) • Example 3: Ammonium salts and soluble bases react as follows (particularly when the solution is warmed): NH4Cl (aq) + NaOH (aq) → NH3 (g) + HOH (l) + NaCl (aq) • The odor of ammonia gas is noted and moist blue litmus paper held near the mouth of the container will turn blue. Theoretically NH4OH, ammonium hydroxide, is produced (also known as ammonia water). The compound is unstable and decomposes into ammonia gas and water: NH4OH (aq) → NH3 (g) + HOH (l) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 64 Double Replacement (Gas) • Example 4: The odor of rotten eggs and bubbling are noted when an acid is added to a sulfide. A typical reaction producing hydrogen sulfide gas is: FeS (s) + 2HCl (aq) → FeCl2 (aq) + H2S (g) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 65 Try It Out 1 • Dilute hydrochloric acid is added to a solution of potassium sulfite. (p. 152) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 66 Try It Out 2 • Concentrated hydrochloric acid is added to solid manganese (II) sulfide. (p. 150) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 67 Today… • Turn in: • Get Out WS#2 • Our Plan: • Questions on WS#2 • Quick Review/Video • Notes – Aqueous Reactions, Net Ionic Equations, & Math with Ion Concentration • Begin WS#3 • Homework (Write in Planner): • WS#3 Due Monday Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 68 A Note about phases • A product can only be aqueous if there is an aqueous or liquid reactant. That’s why some of the ones on the first WS that you labeled aqueous were solid. • Examples: Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 69 Quick Discussion of Weak Electrolytes • One of the driving forces for a reaction is the production of weak electrolytes (water or a weak acid). • For a list of strong acids see page 22 in booklet. Everything else is weak. • The only thing to note is that if you form a weak acid, it is aqueous but you would have a forward arrow, not a double arrow. • See examples on the board. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 70 Quick Review • Solutions of sodium fluoride and dilute hydrochloric acid are combined. • Dilute acetic acid solution is added to solid magnesium carbonate. • A saturated solution of calcium hydroxide was added to a solution of magnesium chloride. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 71 Crash Course in Precipitation • http://www.youtube.com/watch?v=IIu16dy 3ThI Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 72 Arrhenius’s Theory of Electrolytic Dissociation • Why do some solutions conduct electricity? • An early hypothesis was that electricity produced ions in solution, and those ions allowed the electricity to flow. • Arrhenius’s theory: – Certain substances dissociate into cations and anions when dissolved in water. – The ions already present in solution allow electricity to flow. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 73 Electrolytic Properties of Aqueous Solutions • Electrolytes dissociate to produce ions. The more the electrolyte dissociates, the more ions it produces. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 74 Types of Electrolytes • A strong electrolyte dissociates completely. – A strong electrolyte is present in solution almost exclusively as ions. – Strong electrolyte solutions are good conductors. • A nonelectrolyte does not dissociate. – A nonelectrolyte is present in solution almost exclusively as molecules. – Nonelectrolyte solutions do not conduct electricity. • A weak electrolyte dissociates partially. – Weak electrolyte solutions are poor conductors. – Different weak electrolytes dissociate to different extents. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 75 Is it a strong electrolyte, a weak electrolyte, or a nonelectrolyte? • Strong electrolytes include: – Strong acids (HCl, HBr, HI, HNO3, H2SO4, HClO4) – Strong bases (IA and IIA hydroxides) – Most water-soluble ionic compounds • Weak electrolytes include: – Weak acids and weak bases – A few ionic compounds How do we tell whether an acid (or base) is weak? • Nonelectrolytes include: – Most molecular compounds – Most organic compounds (most of them are molecular) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 76 Aqueous Solutions & Ionic Equations • On the AP Exam, you do not have to write out complete molecular equations like we have been doing. • Instead, you have to write ionic equations. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 77 Overall (Total) Ionic Equation • Formulas of the reactants and products are written to show the predominant form of each substance as it exists in aqueous solution. • Soluble salts, strong acids, and strong bases are written as separated ions. Everything else is written as a molecule. • We will memorize strong acids and strong bases later in the year. For now, a list will be provided. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 78 Memorize Later… Strong Acids HClO4 H2SO4 HI HBr HCl HNO3 Prentice Hall © 2005 Strong Bases LiOH RbOH NaOH CsOH KOH Mg(OH)2 Ca(OH)2 Sr(OH)2 Ba(OH)2 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 79 Overall Ionic Equation Example 1 Cd(NO3)2 (aq) + Na2S (aq) → CdS (s) + 2NaNO3 (aq) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 80 Overall Ionic Equation Example 2 CaCO3 (aq) + 2HCl (aq) → CaCl2 (aq) + HOH (l) + CO2 (g) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 81 Try it Out (NH4)2S (aq) + 2LiOH (aq) → Li2S (aq) + 2NH3 (g) + 2HOH (l) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 82 Net Ionic Equation • Net ionic equations are written to show only the species that react or undergo change in aqueous solutions. • The net ionic equation is obtained by eliminating the spectator ions from the overall equation. • All that is left are the ions that have changed chemically. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 83 Net Ionic Equation Example 1 Cd(NO3)2 (aq) + Na2S (aq) → CdS (s) + 2NaNO3 (aq) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 84 Example 2 • For each of these word equations, predict the product and write an overall and net ionic equation. • Copper (I) nitrate is combined with silver chloride. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 85 Example 3 • Magnesium hydroxide is combined with lead (II) sulfate. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 86 Try It Out • Mercury (I) nitrate is combined with sodium sulfide. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 87 Ion Concentrations in Solution • “Trick” question … What is the concentration of Na2SO4 in a solution prepared by diluting 0.010 mol Na2SO4 to 1.00 L? • The answer is: … zero … • WHY?? • And … how do we describe the concentration of this solution? Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 88 Calculating Ion Concentrations in Solution • In 0.010 M Na2SO4: – two moles of Na+ ions are formed for each mole of Na2SO4 in solution, so [Na+] = 0.020 M. – one mole of SO42– ion is formed for each mole of Na2SO4 in solution, so [SO42–] = 0.010 M. • An ion can have only one concentration in a solution, even if the ion has two or more sources. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 89 Example 4.1 Calculate the molarity of each ion in an aqueous solution that is 0.00384 M Na2SO4 and 0.00202 M NaCl. In addition, calculate the total ion concentration of the solution. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 90 Try It Out! • Exercise 4.1A: Seawater is essentially 0.438 M NaCl and 0.0512 M MgCl2, together with several other minor solutes. What are the molarities of Na+1, Mg+2, and Cl-1 in seawater? Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 91 Example 4.6 One cup (about 240 g) of a certain clear chicken broth yields 4.302 g AgCl when excess AgNO3(aq) is added to it. Assuming that all the Cl– is derived from NaCl, what is the mass of NaCl in the sample of broth? Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 92 Stop! • Complete Worksheet #4 by Monday. –Let’s look at it together. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 93 Today… • Turn in: • Get Out WS#3 • Our Plan: • Questions on WS#3 • Quick Review • Notes – Acid/Base Reactions & Titrations • Begin WS#4 • Homework (Write in Planner): • WS#4 Due Wednesday Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 94 Quick Review • Write the molecular and net ionic equation for the following: 1. Chlorine gas is bubbled into a solution of potassium iodide. 2. Aqueous solutions of potassium chromate and silver nitrate react. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 95 Acid-Base Reactions • We will cover acid/base reactions in great detail at the end of the school year. For now, we’re just going to cover very simple neutralization reactions. • Neutralization is the transfer of PROTONS from an acid to a base. • In neutralization, an acid and a base form a salt and water. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 96 Acid-Base Reactions • When writing net ionic equations, keep in mind which acids are strong (written in ionic form) and which are weak (written in molecular form). • Check the solubility rules of the salt produced. If it is soluble, it is written in ionic form; if it is insoluble it is written in molecular form. • The salt produced always consists of a cation from the base and an anion from the acid. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 97 Remember, these are in your notes… Strong Acids HClO4 H2SO4 HI HBr HCl HNO3 Prentice Hall © 2005 Strong Bases LiOH RbOH NaOH CsOH KOH Mg(OH)2 Ca(OH)2 Sr(OH)2 Ba(OH)2 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 98 Acid-Base Reactions • Example 1: Hydrogen sulfide gas is bubbled through excess potassium hydroxide solution. H2S (g) + 2KOH (aq) → K2S (aq) + 2HOH (l) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 99 Acid-Base Reactions • Polyprotic acids (more than one hydrogen like H2SO4) can be tricky. If the base is in excess, all hydrogen ions will react with strong base to produce water. See Example 2. • If however, this same reaction were described in terms of mixing equal numbers of moles, then the coefficients for both reactants would be one (the same number of H and OH must be given away). See Example 3. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 100 Acid-Base Reactions • Example 2: Dilute sulfuric acid is reacted with excess sodium hydroxide. H2SO4 (aq) + 2NaOH (aq) → Na2SO4 (aq) + 2HOH (l) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 101 Acid-Base Reactions • Example 3: Equal number of moles of sulfuric acid and sodium hydroxide react. H2SO4 (aq) + NaOH (aq) → NaHSO4 (aq) + HOH (l) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 102 Acid-Base Reactions • As the following example demonstrates, it is important to take into account the quantity (concentration and amount) of each reactant. • Example 4: Equal volumes of 0.1 M phosphoric acid and 0.2 M sodium hydroxide are reacted together. H3PO4 (aq) + 2NaOH (aq) → Na2HPO4 (aq) + 2HOH (l) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 103 Try It Out 1 • Equal molar volumes of sodium hydroxide and hydrobromic acid are mixed together. Write the molecular equation and the net ionic equation. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 104 Try It Out 2 • Equal volumes of 0.1 M phosphoric acid and potassium hydroxide solutions are mixed. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 105 Titrations • A titration is a procedure where one reactant is carefully added to another reactant until the two have combined in their exact stoichiometric proportions. • There are different types of titrations, but no matter the type, both reactants are fully consumed at the end of the titration. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 106 Titrations • The purpose of a titration is to find the number of moles, grams, concentration, or percentage of an unknown. • The unknown is called the ANALYTE. • This is done by measuring the precise volume and concentration of a known solution (TITRANT) needed to react completely with the analyte. • Stoichiometry is then used to determine whatever quantity you’re looking for. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 107 Acid-Base Titrations • Acid-base titrations are the most common type • You conducted this type of titration in Chem 1 (remember the antacid lab?) • There are 3 things that you need for a titration: – A way to accurately measure the titrant (BURET) – A way to know your reaction is complete (INDICATOR or you can look at a TITRATION CURVE) – A solution whose concentration you know (STANDARD SOLUTION) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 108 Acid-Base Titrations Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 109 Acid-Base Titrations • Equivalence point – in an acid-base titration it is the point when the titrant completely neutralizes the analyte. • If you’re using an indicator, you choose one that changes color close to the neutralization point. • If you are looking at a titration curve, it is the straight line on a graph of volume versus pH. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 110 Acid-Base Titrations • When the indicator changes color in a titration, you have reached the endpoint. • At the endpoint the titration is stopped and the volume of titrant is recorded. • You want the equivalence point and endpoint to be the same! Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 111 Titration Curve Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 112 Calculation Example 1 • Example 4.9: What volume (mL) of 0.210 M NaOH is required to neutralize 20.00 mL of 0.103 M HCl in an acid-base titration? Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 113 Calculation Example 2 • Example 4.10: A 10.00 mL sample of an aqueous solution of calcium hydroxide is neutralized by 23.30 mL of 0.020000 M HNO3 (aq). What is the molarity of the calcium hydroxide solution? Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 114 Stop • Complete Worksheet #4 by next class and complete the pre-lab for Investigation 4. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 115 Today… • Turn in: • Get Out WS#4 • Our Plan: • Questions on WS#4 • Investigation 4 • Homework (Write in Planner): • Lab Report Due Monday • Post results (Average concentration of H3PO4) to Edmodo by Friday. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 116 Quick Review • Equal volumes of 0.1 M sulfuric acid and 0.2 M potassium hydroxide are mixed. Write the balanced molecular and net ionic equation. (p. 148) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 117 Today… • Turn in: • Questions on Lab Report so far? • Our Plan: • Notes – Oxidation Numbers & Redox Titrations • Begin WS#5 (10 minutes) • Sample Test (Pep Assembly Today) • Homework (Write in Planner): • WS#5 Due Monday & Lab Report due Mon Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 119 Redox Reactions • Balancing Redox Equations is complicated. We will spend an entire week at the end of the year working on it. • For now, you just have to identify substances that are oxidized and those that are reduced. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 120 Reactions Involving Oxidation and Reduction • Oxidation: Loss of electrons • Reduction: Gain of electrons • Both oxidation and reduction must occur simultaneously. – A species that loses electrons must lose them to something else (something that gains them). – A species that gains electrons must gain them from something else (something that loses them). • To remember, use the phrase LEO GER or OIL RIG. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 121 A Redox Reaction: Electrons are transferred from Mg metal to Cu2+ ions and … Prentice Hall © 2005 Mg + Cu2+ → Mg2+ + Cu … the products are Cu metal and Mg2+ ions. General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 122 Oxidation Numbers • An oxidation number is the charge on an ion, or a hypothetical charge assigned to an atom in a molecule or polyatomic ion. • Examples: in NaCl, the oxidation number of Na is +1, that of Cl is –1 (the actual charge). • In CO2 (a molecular compound, no ions) the oxidation number of oxygen is –2, because oxygen as an ion would be expected to have a -2 charge. • The carbon in CO2 has an oxidation number of +4 (Why?) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 123 Rules for Assigning Oxidation Numbers 1. For the atoms in a neutral species—an isolated atom, a molecule, or a formula unit— the sum of all the oxidation numbers is 0. 2. For the atoms in an ion, the sum of the oxidation numbers is equal to the charge on the ion. 3. In compounds, the group 1A metals all have an oxidation number of +1 and the group 2A metals all have an oxidation number of +2. 4. In compounds, the oxidation number of fluorine is –1. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 124 Rules for Assigning Oxidation Numbers 5. In compounds, hydrogen has an oxidation number of +1. 6. In most compounds, oxygen has an oxidation number of –2. 7. In binary compounds with metals, group 7A elements have an oxidation number of –1, group 6A elements have an oxidation number of –2, and group 5A elements have an oxidation number of –3. 8. Elements in their standard state (solid, liquid, or gas – look at PT) have an oxidation number of 0. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 125 Identifying Oxidation–Reduction Reactions • In a redox reaction, the oxidation number of a species changes during the reaction. • Oxidation occurs when the oxidation number increases (species loses electrons). • Reduction occurs when the oxidation number decreases (species gains electrons). • If any species is oxidized or reduced in a reaction, that reaction is a redox reaction. • Examples of redox reactions: displacement of an element by another element; combustion; incorporation of an element into a compound, etc. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 126 LEO - GER Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 127 Example 4.7 What are the oxidation numbers assigned to the atoms of each element in (a) KClO4 Prentice Hall © 2005 (b) Cr2O72– (c) CaH2 (d) Na2O2 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry (e) Fe3O4 Chapter Four 128 Example 1 • Which is oxidized and which is reduced in the following equation: Fe2O3 (s) + 3CO (g) → 2Fe (s) + 3CO2 (g) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 129 Example 2: • Which is reduced/oxidized? MnO2 + 4H+1 + 2Cl-1 → Mn+2 + 2H2O + Cl2 Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 130 Oxidation Numbers of Nonmetals • The maximum oxidation number of a nonmetal is equal to the group number. – For nitrogen, +5. – For sulfur, +6. – For chlorine, +7. • The minimum oxidation number is equal to the group number – 8. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 131 Activity Series of Some Metals In the activity series, any metal above another can displace that other metal. Mg metal can react with … … Cu2+ ions to form Cu metal. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Will lead metal react with Fe3+ ions? Will iron metal dissolve in an acid to produce H2 gas? Chapter Four 132 Applications of Oxidation and Reduction • Everyday life: to clean (bleach) our clothes, sanitize our swimming pools (“chlorine”), and to whiten teeth (peroxide). • In foods and nutrition: redox reactions “burn” the foods we eat; antioxidants react with undesirable free radicals. • In industry: to produce iron, steel, other metals, and consumer goods. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 133 Redox Titrations • In a redox titration, one reactant (often the titrant) is an oxidizing agent and the other reactant is a reducing agent. • Permanganate ion, usually from KMnO4, is one of the most commonly used oxidizing agents in the chemical laboratory and makes an excellent titrant. • The math is very similar to that used in acid-base titrations. Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 134 Calculation Example 1 • Example 4.12: A 0.2865 g sample of an iron ore is dissolved in acid, and the iron is converted entirely to Fe+2 (aq). To titrate the resulting solution, 0.02645 L of 0.02250 M KMnO4 (aq) is required. What is the mass percent of iron in the ore? 5Fe+2 (aq) + MnO4-1 (aq) + 8 H+1 (aq) → 5Fe+3 (aq) + Mn+2 (aq) + 4H2O (l) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 135 Calculation Example 2 • Example 4.12A: Suppose the titration in Example 4.12 was carried out with 0.02250 M K2Cr2O7 (aq) rather than KMnO4 (aq). What volume of K2Cr2O7 (aq) would be required? 6Fe+2 (aq) + Cr2O7-2 (aq) + 14H+1 (aq) → 6Fe+3 (aq) + 2Cr+3 (aq) + 7H2O (l) Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 136 Stop! • Complete Worksheet #5 by next class period and finish your titration lab report! Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 137 Today… • Turn in: • Get out WS#5 to Check • Put Lab Report in basket (rubric on top) • Our Plan: • Questions on WS#5 • Worksheet Race • Crash Course Video • Begin Report for Investigation 8 • Homework (Write in Planner): • Lab Report Due Friday Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 139 Crash Course Water & Solutions • Good introduction to redox lab: • http://www.youtube.com/watch?v=AN4Kif V12DA Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 140 Today… • Turn in: • Nothing • Our Plan: • Investigation 8 • Test Review • Homework (Write in Planner): – Test Next Class – Breakfast Club Friday at 6:30 am! Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 141 Today… • Turn in: • Lab Report – rubric on top • Our Plan: • Questions on Test Review • Unit 2 Test • Homework (Write in Planner): • Watch the Alkanes Notes online and complete the booklet to p. 7 Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four 142 Do you feel like this? Prentice Hall © 2005 General Chemistry 4th edition, Hill, Petrucci, McCreary, Perry Chapter Four