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Chemical Reactions, Acids and Bases Honors Chemistry Chemical Reactions What is observed What it means 1. bubbles, inflate bag, disappears, steam, 1. gas formation/release smell, smoke 2. clear to cloudy, solid appears on bottom 2. precipitate (solid) formation 3. flame, light, temperature change 3. change in energy 4. color change 4. color change, e.g. acid-base indicator We only know the products of a chemical reaction for sure by carrying out the reaction in the laboratory BUT we can make general predictions about the products of a reaction based on “types” of chemical reactions. Types of Chemical Reactions (note: not all reactions fit these categories) 1. Synthesis (or Combination) 2. Decomposition 3. Single Replacement 4. Double Replacement (or Metathesis) 5. Combustion 6. Oxidation-Reduction (Redox) (Honors) -1- Chemical Reactions, Acids and Bases Honors Chemistry Sidebar: Energy Changes in Chemical Reactions 1. Exothermic reaction Releases energy (energy = one of the products) C(s) + O2(g) H = -393.5 kJ CO2(g) + 393.5 kJ Energy diagram C + O2 Energy CO2 } Energy released (393.5 kJ) Reactants Products 2. Endothermic reaction Absorbs energy (energy = reactant) CaCO3(s) + 176 kJ H = +176 kJ CaO(s) + CO2(g) Energy diagram CaO + CO2 } Energy absorbed Energy CaCO3 Reactants Products -2- (176 kJ) Chemical Reactions, Acids and Bases Honors Chemistry Types of Chemical Reactions 1. Synthesis (Combination) *usually produces energy - exothermic: A + X AX (one product) Examples: a) metal + nonmetal (often oxygen) Cu + O2 Cu2O (Copper I) Cu + O2 CuO (Copper II) Na + Br2 NaBr b) nonmetal + nonmetal N2 + O2 NO2 c) metal oxide + water base (Honors) MgO + H2O Mg(OH)2 d) nonmetal oxide + water acid (Honors) CO2 + H2O H2CO3 2. Decomposition *usually requires energy - endothermic AB or or light one reactant A+B > one product a) compound 2 elements Ag2O Ag + O2 b) reactant elements (electrolysis) (Demo: record your observations) H2O H2 + O2 c) metal carbonate metal oxide + carbon dioxide (Honors) MgCO3 MgO + CO2 d) acid nonmetal oxide + water H2CO3 CO2 + H2O -3- (Honors) Chemical Reactions, Acids and Bases Honors Chemistry Practice • Write balanced chemical equations for the following chemical reactions. • Figure out what the states of matter should be at room temperature. • Predict products according to the type of reaction Synthesis: 1. carbon + oxygen 2. gallium + oxygen 3. nitrogen + hydrogen (H) 4. phosphorus (V) oxide + water (H) 5. calcium oxide + water Decomposition: 1. sodium oxide 2. aluminum chloride (H) 3. calcium carbonate (H) 4. potassium chlorate -4- Chemical Reactions, Acids and Bases Honors Chemistry 3. Single Replacement Reactions A + BX AX + B Y + BX BY + X or *Use activity series: higher replaces lower *Use HOH for H2O Three types of cation replacement: a) metal replaces metal Mg(s) + SnCl2(aq) MgCl2(aq) + Sn(s) b) metal replaces H in H2O K(s) + HOH(l) KOH(aq) + H2(g) c) metal replaces H in acid Fe(s) + H2SO4(aq) FeSO4(aq) + H2(g) Anion replacement: Br2(l) + SrI2(aq) SrBr2(aq) + I2(s) halogen replaces halogen Demonstration – Single Replacement Use the activity series on your reference sheet to predict the products of the following reactions: Cu(s) + AgNO3(aq) Ag(s) + Cu(NO3)2(aq) Practice 1. For each of the following pairs of elements, circle the one that would replace the other element in a compound. a. calcium, tin e. iron, copper b. bromine, fluorine f. iodine, chlorine c. aluminum, potassium g. silver, lead d. zinc, calcium -5- Chemical Reactions, Acids and Bases Honors Chemistry 2. For each of the following reactants, use the activity series to determine whether the reaction would take place or not. If no reaction takes place, write NR in the blank. If a reaction does take place, write the formulas for the products of the reaction. (Hint: If an active metal replaces the hydrogen in water, the hydroxide of the active metal forms. H-OH) a. Li(s) + Fe(NO3)3(aq) _________ b. Au(s) + HCl(aq) __________ c. Cl2(g) + KBr(aq) ___________ d. Cu(s) + Al(NO3)3(aq) ________ e. Ag(s) + HBr(aq) _________ f. Ni(s) + SnCl2(aq) ___________ 3. Magnesium metal can be used to remove tarnish from silver items. Silver tarnish is the corrosion that occurs when silver metal reacts with substances in the environment, especially those containing sulfur. Why would magnesium remove tarnish from silver? 4. Use the activity series for metals to explain why copper metal is used in plumbing where the water might contain compounds of many different metals. 5. The last four metals in the activity series of metals are commonly referred to as the “coinage metals”. Why would these metals be chosen over more active metals for use in coins? Why do you think some more active metals, such as zinc or nickel, are sometimes used in coins? -6- Chemical Reactions, Acids and Bases Honors Chemistry 4. Double Replacement AX + BY BX + AY (aq) (aq) (aq) forms: ppt H2O gas } a) ppt-forming: If both products are aqueous NR If not, NR* Pb(NO3)2(aq) + KI(aq) KNO3(aq) + PbI2(s) (Use SolubilitiesTable to predict products – see reference sheet) b) water-forming: H2SO4(aq) + NaOH(aq) Na2SO4(aq) + H2O(l) acid + base salt + water c) gas-forming (e.g. CO2 from a 2o decomposition rxn) NaHCO3(aq) + HC2H3O2(aq) NaC2H3O2(aq) + H2O(l) + CO2(g) Practice – Single Replacement and Double Replacement Reactions Use the activity series or solubility table to predict the product of the following reactions: Na(s) + SrBr2(aq) CrI3(aq) + KCl(aq) Zn(s) + H2SO3(aq) K2CO3(aq) + HI(aq) Na(s) + H2O(l) HC2H3O2(aq) + (NH4)2S(aq) Fe(s) + CuCl2(aq) HBr(aq) + Ba(OH)2(aq) -7- Chemical Reactions, Acids and Bases Honors Chemistry 5. Combustion: Hydrocarbon + oxygen carbon dioxide + water a) complete - forms CO2 + H2O: CH4 + O2 CO2 + H2O + Energy b) incomplete - forms CO + H2O: CH4 + O2 CO + H2O + Energy (Honors) Balancing Combustion Reactions e.g. C2H2 + O2 CO2 + H2O 1. Balance hydrogens, but at the same time make the number of oxygens in H2O even by doubling the coefficient if necessary – do NOT balance the oxygens at this point! (i.e. make the number of Hs in the reactants divisible by 4) C2H2 + O2 CO2 + H2O 2 C2H2 + O2 CO2 + 2 H2O 2. Balance carbons 2 C2H2 + O2 4 CO2 + 2 H2O 3. Lastly, balance the oxygen molecules on the left 2 C2H2 + 5 O2 4 CO2 + 2 H2O 2 C2H2 + 5 O2 4 CO2 + 2 H2O Practice Write balanced chemical equations for the complete combustion of • propane (C3H8) • pentane (C5H12) • hexane (C6H14) • decane (C10H22) • ethyl alcohol (C2H5OH) -8- Chemical Reactions, Acids and Bases Honors Chemistry Total and Net Ionic Equations • Balanced Formula Equation: 2 KOH(aq) + H2SO4(aq) K2SO4(aq) + H2O(l) • Total Ionic Equation: 2 K+ + 2 OH-(aq) + 2 H+ + SO42-(aq) 2 K+ + SO42-(aq) + 2 H2O(l) • Net Ionic Equation: 2 OH-(aq) + 2 H+ H2O(l) 1. What is a spectator ion? 2. What are the spectator ions in this reaction? 3. Compare and contrast each pair below. a. balanced formula equations, total ionic equations b. total ionic equations, net ionic equations 4. For the reaction between aqueous silver nitrate and aqueous sodium chloride, write each of the following. The products of the reaction are aqueous sodium nitrate and solid silver chloride. a. balanced formula equation b. total ionic equation c. net ionic equation 5. What is the net ionic equation for the reaction between aqueous calcium hydroxide and nitric acid? The products of this reaction are aqueous calcium nitrate and water. How does this net ionic equation compare to the net ionic equation shown at the top of this page? Hint: you may want to begin with the balanced formula equation, then total ionic equation.) -9- Chemical Reactions, Acids and Bases Honors Chemistry 6. Oxidation-Reduction (Redox) Reactions Electrons are transferred from one atom to another. Note that when one substance is oxidized, another compound must be reduced, and viceversa. Oxidation = - electrons from a substance Reduction = + electrons to a substance Mg(s) + 2 HCl(aq) MgCl2(aq) + H2(g) 0 +1 -1 +2 -1 0 • • • Note: The transfer of electrons during oxidation-reduction reactions often produce energy (when spontaneous), which can be in the form of electricity. LEO the lion says GER (Loss of Electrons = Oxidation/Gain of Electrons = Reduction) OIL RIG (oxidation is loss and reduction is gain) Examples: a) Combustion: “rapid oxidation reaction in which a large amount of heat and usually light are released” C + O2 CO2, CO S + O2 SO2 What was oxidized? What was reduced? b) Metal + acid (SR): e.g. Zn(s) + 2 HCl(aq) ZnCl2(aq) + H2(g) Total ionic equation: What was oxidized? What was reduced? c) Metal + salt (SR): e.g. Mg(s) + CoSO4(aq) MgSO4(aq) + Co(s) Total ionic equation: What was oxidized? What was reduced? Oxidation numbers help us keep track of what happens to the electrons in reactions. - 10 - Chemical Reactions, Acids and Bases Honors Chemistry Practice Identify redox pairs and oxidation numbers. Write net ionic equations for the following reactions. 2 Na(s) + SrBr2(aq) Sr(s) + 2 NaBr(aq) Zn(s) + H2SO3(aq) ZnSO3(aq) + H2(g) 2 Na(s) + 2 H2O(l) 2 NaOH(aq) + H2(g) Fe(s) + CuCl2(aq) Cu(s) + FeCl2(aq) Predicting Products of Different Reaction Types Class of reaction Synthesis Decomposition Reactants two or more substances one compound Single Replacement a metal and a compound Double Replacement a nonmetal (halogen) and a compound two compounds dissolved in water hydrocarbon + oxygen Combustion (restricted definition) Oxidation-Reduction (Honors) one or more substances - 11 - Probable Products Chemical Reactions, Acids and Bases 1. Honors Chemistry For each set of reactants listed below, identify the type of reaction that the reactants might undergo. List as many reaction types as may apply. Assume that all the reactants for the reaction are listed. a. a compound and an element b. two compounds c. one compound 2. For each set of reactant products listed below, identify the type of reaction that might have formed the products. List as many reaction types as may apply. Assume that all the productions for the reaction are listed. a. a compound and an element b. two compounds c. one compound 3. Classify each of the following examples according to the type of reaction involved. List as many reaction types as may apply. a. A match burns b. The carbonic acid found in soft drinks breaks down into bubbles of carbon dioxide and water c. Phosphorus and oxygen react rapidly, forming diphosphorus pentoxide d. An iron nail is placed into a copper sulfate solution. Copper metal appears on the nail. e. The acid in baking powder reacts with baking soda (NaHCO3), forming carbon dioxide gas and other products. f. Water and sulfur trioxide react to form sulfuric acid. g. Copper wire is placed in a silver nitrate solution. The solution turns blue, which is the color of the copper ion, and solid silver forms on the wire. - 12 - Chemical Reactions, Acids and Bases Honors Chemistry Properties of Acids and Bases When dissolved in water: Acids Bases taste sour taste bitter feel wet feel slippery turn blue litmus paper pink/red turn red litmus paper blue conduct electricity conduct electricity react with most metals do not react with most metals contain more H+ than OH- contain more OH- than H+ pH < 7 pH > 7 Strong acid + strong base salt + H2O Arrhenius (traditional) acids and bases (C19th) Acid: compound containing H that ionizes to yield H+ in solution HCl(g) H2O H+(aq) + Cl-(aq) or HCl(g) + H2O(l) H3O+(aq) + Cl-(aq) Base: compound containing OH that ionizes to yield OH- in solution H2O NaOH(s) Na+(aq) + OH-(aq) Autoionization of water: H2O + H2O H3O+ + OHIn pure water: [H3O+] = 1.0 x 10-7 M and [OH-] = 1.0 x 10-7 M If we add acid [H3O+] increases and [OH-] decreases [H3O+] = 1.0 x 10-4 M [OH-] = 1.0 x 10-10 M If we add base, the reverse is true: [H3O+] = 1.0 x 10-4 M [OH-] = 1.0 x 10-10 M What is the product of [H3O+][OH-] in each case? - 13 - Chemical Reactions, Acids and Bases Honors Chemistry pH = - log [H+] pOH = - log [OH-] = - log (1.0 x 10-7) = - log (1.0 x 10-7) = -(-7) = -(-7) =7 =7 basis of neutral pH 7: [H+] = [OH-] Concentration, pH and pOH Concentration is given in terms of molarity (M) Concentration of H+ = [H+] = = 0.0100 mol H+ = 0.0100 M H+ L In scientific notation [H+] = 1.00 x 10-2 M Find pH: pH = - log [H+] pH = 2 Find pOH: pOH = - log [OH-] and pH + pOH pOH = 12 Find [OH-]: [OH-] = 10-pOH = 10-12 [OH-] = 1.00 x 10-12 M Converting between concentration and pH (from slide) Practice pH + pOH = 14; pH = -log[H+]; pOH = -log[OH-] When pH = 2 When pOH = 8 [H+] = _______ M [OH-] = ______M pOH = _______ pH = _______ [OH-] = ______ M [H+] = _______ M [H+] = 1.0 x 10-3 M. What is the [OH-]? _____________ More Practice 1. What is the pH of a solution with a [H+] of 10-8 M? ________ 2. What is the pOH of a solution with a [OH-] of 10-11 M? ________ 3. What is the pH of a solution with a [OH-] of 10-2 M? ________ 4. What is the pOH of a solution with a [H+] = 10-5 M? ________ - 14 - Chemical Reactions, Acids and Bases Honors Chemistry 5. Which is more acidic, a solution with a pH of 6 or one with a pH of 9? __________ 6. Which is more basic, a solution with a pOH of 7 or one with a pOH of 12? _________ 7. Which is more acidic, a solution with a pH of 5 or one with a pOH of 10? ______ 8. Which is more basic, a solution with a pH of 8 or one with a pOH of 12? _____ 9. Stomach contents can have a pH of 3. Are stomach contents acidic, basic or neutral? _______ 10. Pure water has a pOH of 7. Is pure water acidic, basic or neutral? __________ 11. Normal rain has a pH of approximately 6. Is normal rain strongly acidic, slightly acidic, neutral, slightly basic, or strongly basic? ________ 12. Acid precipitation is often a problem in industrialized areas. What might you expect the pH of acid rain to be? _______________________ Strengths of Acids and Bases Strong acid or base – ionizes/dissociates completely in water [H+] or [OH-] = conc. of acid or base. e.g. HCl, NaOH. 5 units of acid – 5 out of 5 dissociated: H+ Cl- H+ Cl- H+ Cl- H+ Cl- H+ Cl- Weak acid or base – ionizes/dissociates only partially in water [H+] or [OH-] < conc. of acid or base. e.g. HC2H3O2, NH3 5 units – only 1 out of 5 dissociated: HC2H3O2 HC2H3O2 HC2H3O2 HC2H3O2 Strong concentrated Weak dilute Strong acid: Strong base: HCl + H2O H3O+ + Cl- H2O NaOH Na+ + OH- 1.0 x 10-2 M ?M ?M 1.0 x 10-2 M pH = ? ?M pH = ? Weak base: Weak acid: HC2H3O2 + H2O H3O+ + C2H3O21.0 x 10-2 M NH3 + H2O NH4+ + OH1.0 x 10-2 M ?M ?M pH = ? pH = ? - 15 - H+ C2H3O2- Chemical Reactions, Acids and Bases Honors Chemistry Demo - Strong and Dilute vs. Weak and Concentrated Acids and Bases Acids: Strong HCl Weak HC2H3O2 Weak HC2H3O2 Dilute Dilute Concentrated 0.01 M 0.01 M 1M pH = pH = pH = Strong NaOH Weak NH3 Weak NH3 Dilute Dilute Concentrated 0.01 M 0.01 M 1M pH = pH = pH = Bases: What do you think? Are the following acidic, basic or neutral? table salt vinegar rubbing alcohol window cleaner distilled water lemon juice soap drain cleaner applesauce blood What is the difference between a strong acid and a concentrated acid? A weak acid and a dilute acid? - 16 -