Slide 1 / 142 Slide 2 / 142 Chemical Reactions Slide 3 / 142 Slide 4 / 142 Table of Contents: Chemical Reactions Chemical Equations Balancing Equations Types of Chemical Reactions Precipitation Reactions Net Ionic Equations Click on the topic to go to that section Chemical Equations Oxidation-Reduction Reactions Types of Oxidation-Reduction Reactions Acid-Base Reactions Identifying Reaction Types: Summary Return to Table of Contents Slide 5 / 142 Chemical Equations Chemical equations are concise representations of chemical reactions. Slide 6 / 142 Chemical Equations The formulas of the reactants (on the left) are connected by an arrow with the formulas of the products (on the right). To write a word equation, write the names of the reactants to the left of the arrow separated by plus signs. Write the names of the products to the right of the arrow, also separated by plus signs. + --> + CH 4(g) + 2O 2(g) --> CO 2(g) + 2H 2O(g) Reactant + Reactant Product + Product
Slide 7 / 142 Symbols used in chemical equations Slide 8 / 142 Skeleton equations A skeleton equation is a chemical equation that does not indicate the relative amounts of the reactants and products. Write the formulas of the reactants to the left of the yields sign (arrow) and the formulas of the products to the right. Here is the equation for rusting: Metallic Iron reacts with oxygen in the air to produce iron (III) oxide (rust). Iron( metal) + Oxygen ( gas) iron (III) oxide ( solid) (word equation) Fe + O2 # Fe2O3 ( skeleton /chemical equation) Slide 9 / 142 Word Equations When ignited, methane gas reacts with oxygen gas to produce carbon dioxide and steam. + + Slide 10 / 142 1 In the reaction CH4 (g) + O2 (g) # H2O (g) + CO2 (g) the products are: A B C oxygen and water carbon dioxide and water oxygen and methane CH4 gas O2 gas CO2 gas This "skeleton" equation is not balanced: H2O gas D E methane and carbon dioxide I don't know the to this. CH4 (g) + O2 (g) H2O (g) + CO2 (g) Slide 11 / 142 2 In the reaction CH4 (g) + O2 (g) # H2O (g) + CO2 (g) the products are: Slide 12 / 142 Word equations to Chemical equations A B solids liquids Solid potasium chlorate decomposes in air to produce solid potassium chloride and oxygen gas. C gases The word equation is: D dissolved in water (aqueous) potasium chlorate (s) --> potassium chloride (s) + oxygen (g) E F cannot be determined I don't know how to this. The unbalanced "skeleton" equation is: KClO3(s) KCl(s) + O2(g)
Slide 13 / 142 Word equations to Chemical equations Slide 14 / 142 Law of Conservation of Mass Write the word equation, then the skeleton equation Aluminum sulfate reacts with calcium chloride to produce calcium sulfate and aluminum chloride Aluminum sulfate + calcium chloride --> calcium sulfate + aluminum chloride Slide for Word equation Slide for Skeleton equation Al2(SO4)3 + CaCl2 --> Ca(SO4) + AlCl3 We may lay it down as an incontestable axiom that, in all the operations of art and nature, nothing is created; an equal amount of matter exists both before and after the experiment. Upon this principle, the whole art of performing chemical experiments depends. --Antoine Lavoisier, 1789 Slide 15 / 142 Slide 16 / 142 Balancing Equations To write a balanced chemical equation, first write the skeleton equation. Then use coefficients to balance the equation so that it obeys the law of conservation of mass. This is a balanced equation for making a bicycle. The numbers are called coefficients small whole numbers that are placed in front of the formulas in an equation in order to balance it. Return to Table of Contents Slide 17 / 142 Slide 18 / 142 CH4 (g) + 2 O2 (g) # CO2 (g) + 2 H2O (g) 1C 4H Reactants appear on the left side of the equation. 4 O 1C 2 O 2 O 4H Products appear on the right side of the equation. CH 4 (g) + 2 O 2 (g) # CO 2 (g) + 2 H 2O (g) 1C 4H 4 O 1C 2 O 2 O 4H Coefficients are inserted to balance the equation. The states of the reactants and products are written in parentheses to the right of each compound.
Slide 19 / 142 Subscripts and Coefficients Slide 20 / 142 3 How many oxygen atoms are in one formula unit of calcium nitrate? (First, write the formula for calcium nitrate.) Subscripts tell the number of atoms of each element in a molecule. Coefficients tell the number of representative particles (atoms, molecules, or formula units). A 2 B 3 C 5 D 6 E I don't know how to this. Slide 21 / 142 Slide 22 / 142 4 How many nitrogen atoms are in one formula unit of ammonium sulfate? Slide 23 / 142 Write a balanced chemical equation for this reaction. First write a skeleton equation chlorine + sodium bromide # bromine + sodium chloride Cl2 + NaBr # # Br2 + NaCl Slide 24 / 142 Then, count up the number of each type of element on each side of the reaction Cl2 + NaBr # # Br2 + NaCl Reactants Cl: 2 Cl: 1 Na: 1 Na: 1 Products Br: 1 Br: 2
Slide 25 / 142 Next, identify one element that is not balanced. It is best to start with an easy element. The fewer places an element appears on both sides of a reaction, the easier it will be to balance. Cl2 + NaBr # # Br2 + NaCl Reactants Cl: 2 Cl: 1 Na: 1 Na: 1 Br: 1 Br: 2 Products Slide 26 / 142 Identify the side that needs more of that particular element. Cl2 + NaBr # # Br2 + NaCl Reactants Products Cl: 2 Cl: 1 Na: 1 Na: 1 Br: 1 Br: 2 Slide 27 / 142 Determine which molecule or element will be getting the coefficient. In this case, because we need more chlorine on the products side, we will have to add a coefficent to the NaCl, since that is the only product containing chlorine. Slide 28 / 142 To figure out what the coefficient should be, simply take the amount of that specific element you need from the molecule, and divide by the amount of the element you have in the molecule. Cl: 2 Cl2 + NaBr # # Br2 + NaCl Reactants Products Cl: 2 Na: 1 Cl: 1 Na: 1 Br: Na: 1 Br: 1 Br: 2 Cl: 2 Cl2 + NaBr # # Br2 + NaCl 2 Reactants Cl: 2 Cl: 1 Na: 1 Na: 1 Na: 1 Br: 1 Br: 1 Br: 2 Products Need Have = 2 1 = 2 If this is not a whole number, simply multiply ALL the substances in the reaction by some whole number to make the coefficients whole numbers. Slide 29 / 142 Now, just reevaluate the amount of each element on the table Cl2 + NaBr # # Br2 + 2NaCl Cl: 2 Reactants Products Cl: 2 Na: 1 Cl: 1 2 Na: 1 Br: Na: 1 2 Br: 1 Br: 2 Slide 30 / 142 Continue with these steps until all the elements are balanced. When all the elements exist in equal amounts on both sides of the equation, you have a balanced chemical equation. Cl: 2 Cl2 + 2NaBr # # Br2 + 2NaCl Reactants Cl: 2 Cl: 1 2 Na: 1 Na: 1 2 Na: 1 2 Br: Br: 1 2 Br: 2 Products
Slide 31 / 142 SPECIAL NOTE: Make sure that when you are calculating your coefficents you are only looking at the amounts needed/had by individual elements or molecules Cl: 2 CH 3OH + O 2 # # CO 2+ 2H 2O Reactants C: 1 C: 1 Na: 1 H: 4 H: 2 4 Br: 1 O: 1+2=3 O: 2+1=3 2+2=4 Products Slide 32 / 142 SPECIAL NOTE: Here is the incorrect way to evaluate the coefficent in this case Cl: 2 CH 3OH + O 2 # # CO 2+ 2H 2O Reactants C: 1 C: 1 Na: 1 H: 4 H: 2 4 Br: 1 O: 1+2=3 O: 2+1=3 2+2=4 Need Have Products = 4 3 = WRONG!!! Slide 33 / 142 SPECIAL NOTE: Here is the correct way to evaluate the coefficent in this case Cl: 2 CH 3OH + O 2 # # CO 2+ 2H 2O Reactants C: 1 C: 1 Na: 1 H: 4 H: 2 4 Br: 1 O: 1+2=3 O: 2+1=3 2+2=4 Need Have = 4-1 2 = Products Because we already have 1 Oxygen from CH3OH, we only need 3 Oxygen from O2 Because O2 only has 2 Oxygen, the denominator must be 2. 3 2 Slide 34 / 142 SPECIAL NOTE: Remember to make sure you get rid of ALL fractions. Cl: 2 3 2CH 3OH + 2x O 2 # # 2CO 2+ 2x2H 2 2O Reactants C: 1 2 C: 1 2 Na: 1 H: 4 8 H: 2 4 8 Br: 1 Products O: 1+2=3 2+6=8 O: 2+1=3 2+2=4 4+4=8 Slide 35 / 142 If you follow these steps, you'll be able to balance any type of reaction. Cl: 2 2CH 3OH + 3O 2 # # 2CO 2+ 4H 2O Reactants C: 1 2 C: 1 2 Na: 1 H: 4 8 H: 2 4 8 Br: 1 Products O: 1+2=3 2+6=8 O: 2+1=3 2+2=4 4+4=8 Slide 36 / 142 5 When the following equation is balanced, the coefficients are: Na + O 2 # Na 2O A 1, 1, 1 B 1, 2, 4 C 4, 1, 2 D 2, 2, 1 E 4, 1, 4
Slide 37 / 142 Slide 38 / 142 6 When the following equation is balanced, the coefficients are 7 When the following equation is balanced, the coefficients are HgO # Hg + O 2 Al + ZnCl2 # Zn + AlCl3 A 1, 1, 1 B 1, 2, 4 C 4, 1, 2 D 2, 2, 1 E 4, 1, 4 A 1, 1, 1, 1 B 4, 7, 4, 6 C 2, 3, 2, 3 D 1, 3, 1, 2 E 2, 3, 3, 2 Slide 39 / 142 Slide 40 / 142 8 When the following equation is balanced, the coefficients are 9 When the following equation is balanced, the coefficients are NaCl + CaI2 # NaI + CaCl2 NH 3 + O 2 # NO 2 + H 2O A 1, 1, 1, 1 B 3, 2, 2, 3 C 2, 3, 2, 3 D 1, 3, 1, 2 E 2, 1, 2, 1 A 1, 1, 1, 1 B 4, 7, 4, 6 C 2, 3, 2, 3 D 1, 3, 1, 2 E 4, 3, 4, 3 Slide 41 / 142 Slide 42 / 142 10 When the following equation is balanced, the coefficients are Reaction Types Most reactions can be classified as one of the following: Al(NO3)3 + Na2S # Al2S3 + NaNO3 A 2, 3, 1, 6 B 2, 1, 3, 2 C 1, 1, 1, 1 D 4, 6, 3, 2 Precipitation: formation of insoluble product out of aqueous solutions Oxidation/Reduction: exchange of electrons between atoms/ions E 2, 3, 2, 3 Acid/Base: reaction between acids and bases
Slide 43 / 142 Slide 44 / 142 Precipitation Reactions Precipitation Reactions The giant clam's shell is made from the precipitation of CaCO 3 Return to Table of Contents Slide 45 / 142 Precipitation Reactions Precipitation reactions involve the reaction of water soluble ionic compounds to form a water insoluble product called a precipitate: AgNO 3(aq) + HCl(aq) --> AgCl(s) + HNO 3(aq) Slide 46 / 142 Precipitation Reactions One must know which ionic compounds are water soluble and which are not. It is the insoluble ones that form precipitates! ALWAYS SOLUBLE Some general rules apply: NH4+, C2H3O2-, ClO3-, Group 1 A metal ions, NO3- SOMETIMES SOLUBLE Cl-,Br-, I- except when combined with Ag+, Hg+, and Pb 2+ SO4 2- except when combined with Ag+, Hg+, Pb 2+, Ca 2+, Sr 2+, Ba 2+ AgCl precipitate INSOLUBLE (unless paired with a soluble ion) CO3 2-, PO4 3-, OH-, S 2-, F-, O 2- Slide 47 / 142 11 Which one of the following would be INSOLUBLE in water? Slide 48 / 142 12 Which of the following would be MOST SOLUBLE in water? A Na 2CO 3 B NH 4NO 3 C AgNO 3 D Mg(OH) 2 E KCl A CaSO 4 B PbF 2 C PbI 2 D Cu(OH) 2 E CuSO 4
Slide 49 / 142 Solubilities Slide 50 / 142 Solubility Chart A solubility chart provides more exact information as to the individual solubilities of various ionic substances. Note that S on this chart means that the compound is soluble. When you write a chemical equation, it will be (aq) aqueous. Insoluble compounds are shown with the letter I. When you write a chemical equation, it will be (s) solid. Slide 51 / 142 Double Displacement Reactions Slide 52 / 142 Precipitation Reactions Precipitation reactions are often called "double replacement" or "double displacement" reactions because it appears as if the ions switch places with each other. NaCl(aq) + AgNO 3(aq) --> AgCl(s) + NaNO 3(aq) Some examples of precipitation reactions... Pb(NO 3) 2(aq) + 2 KI(aq) # PbI 2(s) + 2 KNO 3(aq) AgNO3(aq) + KCl(aq) # AgCl(s) + KNO3(aq) Na+ and Ag+ switch places The formation of an insoluble precipitate is the driving force of these reactions Slide 53 / 142 Precipitation Reactions Slide 54 / 142 Precipitation Reactions A precipitation reaction will NOT occur if both products are water soluble... 2NaNO 3(aq) + MgCl 2(aq) --> 2NaCl(aq) + Mg(NO 3) 2(aq) Predict the products of this reaction: potassium phosphate + magnesium chloride --> Answer K 3PO 4 (aq) + MgCl 2 (aq) --> KCl + Mg 3(PO 4) 2 Since both products are soluble, no reaction occurs Now, put in the phases of the products and balance the equation. 2K 3PO 4 (aq) + 3MgCl 2 (aq) Answer --> 6KCl(aq) + Mg 3(PO 4) 2(s)
Slide 55 / 142 Precipitation Reactions Predict the products of this reaction: calcium fluoride + sodium sulfate --> CaF 2 (aq) + Na 2SO 4 (aq) --> NaF + Ca(SO 4) (s) Now, put in the phases of the products and balance the equation. Answer Answer CaF2 (aq) + Na2SO4 (aq) --> 2NaF (aq) + Ca(SO4)(s) Slide 56 / 142 13 Which of the following would be products from the reaction of aqueous Mg(C 2H 3O 2) 2 with aqueous Na 3PO 4? A Mg 3(PO 4) 2(aq) + NaC 2H 3O 2(aq) B Mg 3(PO 4) 2(s) + NaC 2H 3O 2(aq) C Mg 3(PO 4) 2(aq) + NaC 2H 3O 2(s) D Mg 3(PO 4) 2(s) + NaC 2H 3O 2(s) E Mg 3(PO 4) 2(s) + NaC 2H 3O 2(s) Slide 57 / 142 14 One of the products of a reaction between silver nitrate and potassium carbonate will be: A silver potassium(aq) Slide 58 / 142 Precipitation Reactions In order to better represent what is actually happening in a precipitation reaction, two things must be accounted for: B potassium carbonate(aq) 1. The ions that comprise a soluble ionic compound are separated when dissolved in water. For example... C nitrate carbonate(aq) NaCl(aq) + AgNO3(aq) --> AgCl(s) + NaNO3(aq) D potassium nitrate(aq) can be written in ionic form as E potassium carbonate(s) Na+(aq) + Cl-(aq) + Ag+(aq) + NO3(aq)- --> AgCl(s) + Na+(aq) + NO3-(aq) Slide 59 / 142 Slide 60 / 142 Precipitation Reactions In order to better represent what is actually happening in a precipitation reaction, two things must be accounted for: 2. Ions not involved in the reaction (not involved in the formation of the precipitate) are called spectator ions and can be eliminated. Reactions written this way are called Net Ionic Equations. Ag+(aq) + Cl-(aq) --> AgCl(s) The complete ionic equation shows all aqueous substances (i.e. strong acids, strong bases, and soluble ionic compounds) dissociated into their ions. For example: Precipitation Reactions NaCl (aq) would be written as Na + (aq) + Cl - (aq) Note: all ionic compound if soluble in water will readily dissociate into the corresponding (+) and (-) ions.
Slide 61 / 142 Slide 62 / 142 Writing Net Ionic Equations Net Ionic Equations The equation between silver nitrate and potassium chloride would normally be shown as AgNO 3 (aq) + KCl(aq) --->AgCl (s) + KNO 3 (aq) However, when all the aqueous species are dissociated into their respective ions, it becomes: Ag + (aq) + NO3 - (aq) + K + (aq) + Cl - (aq) --->AgCl (s) + K + (aq) + NO3 - (aq) Return to Table of Contents This is called the complete ionic equation. Note that the insoluble product does not dissociate. Slide 63 / 142 Spectator Ions Ag (aq) + NO3 - (aq) + K + (aq) + Cl - (aq) --->AgCl (s) + K + (aq) + NO3 - (aq) As this example shows, certain ions are present both before and after the reaction. Because they play no significant role in the reaction, they are known as "spectator ions." A spectator ion is an ion that appears on both sides of an equation and is not directly involved in the reaction. Slide 64 / 142 Writing Net Ionic Equations The net ionic equation is an equation for a reaction in solution that shows only those particles that are directly involved in the chemical change. To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. In other words, cancel out the spectator ions. Ag (aq) + NO3 - (aq) + K + (aq) + Cl - (aq) --->AgCl (s) + K + (aq) + NO3 - (aq) Slide 65 / 142 Writing Net Ionic Equations Slide 66 / 142 Steps for Net Ionic Equations Ag + (aq) + NO 3- (aq) + K + (aq) + Cl - (aq) AgCl (s) + K + (aq) + NO 3- (aq) Write a balanced molecular equation. After cancelling out the spectator ions, the only things left in the equation are those things that change, or react, during the course of the reaction. Ag + (aq) + Cl - (aq) AgCl (s) This is called the net ionic equation.
Slide 67 / 142 Steps for Net Ionic Equations Slide 68 / 142 Steps for Net Ionic Equations Write a balanced molecular equation. Dissociate any reactants or products that are aqueous. All solids, liquids, and gases stay intact and do not dissociate. Write a balanced molecular equation. Dissociate any reactants or products that are aqueous. All solids, liquids, and gases stay intact and do not dissociate. Cross out anything that remains unchanged from the left side to the right side of the equation. Slide 69 / 142 Steps for Net Ionic Equations Write a balanced molecular equation. Dissociate any reactants or products that are aqueous. All solids, liquids, and gases stay intact and do not dissociate. Cross out anything that remains unchanged from the left side to the right side of the equation. Write the net ionic equation with the species that remain. In all cases (involving double replacement), it will be the reaction between the ions that produces the insoluble precipitate. Slide 70 / 142 Example Net Ionic Equation Write a balanced molecular equation. Pb(NO3)2 (aq)+ 2 KI (aq) --> PbI2 (s)+ 2 KNO3 (aq) Dissociate any reactants or products that are aqueous. Pb 2+ (aq) + 2NO3 - (aq)+ 2K + (aq)+ 2I - (aq)# PbI2 (s)+ 2K + (aq)+ 2NO3 - (aq) Cross out anything that remains unchanged from the left side to the right side of the equation. Pb 2+ (aq) + 2NO3 - (aq)+ 2K + (aq)+ 2I - (aq)# PbI2 (s)+ 2K + (aq)+ 2NO3 - (aq) Write the net ionic equation with the species that remain. Pb 2+ (aq) + 2 I - (aq) --> PbI2 (s) Slide 71 / 142 Slide 72 / 142 [*] Writing Net Ionic Equations [*] Writing Net Ionic Equations Practice writing the balanced equation, complete ionic equation and net ionic equation for these reactions. 1. calcium nitrate (aq) and potassium carbonate (aq) ---> Practice writing the balanced equation, complete ionic equation and net ionic equation for these reactions. 2. silver nitrate (aq) and sodium phosphate (aq) --> Ca (aq) + 2+ CO3 (aq) --> 2- CaCO3 (s) Slide for Answer 3Ag (aq) + + PO4 (aq) --> 3- Ag3PO4 Slide for Answer (s)
Slide 73 / 142 15 Which of the following would be a correct net-ionic equation between aqueous BaCl 2 and aqueous NaOH? A Na+(aq) + OH-(aq) + Ba2+ (aq) + Cl-(aq) -->NaBa(s) + ClOH(aq) B Ba2+ (aq) + 2Cl-(aq) --> BaCl2(s) C Ba2+ (aq) + 2OH-(aq) --> Ba(OH)2(s) D Na+(aq) + Cl-(aq) --> NaCl(s) E Na+(aq) + OH-(aq) + Ba2+ (aq) + 2Cl-(aq) -->Ba(OH)2(s) + NaCl(aq) Slide 74 / 142 16 Which of the following aqueous solutions could be used to form a precipitate with MgSO 4? A NaCl B NH 4NO 3 C BaI 2 D KC 2H 3O 2 E LiClO 3 Slide 75 / 142 17 Which of the following would be spectator ions when aqueous lead(ii)nitrate and sodium iodide are mixed? A Pb 2+ and I- B NO 3- and Na+ C NO 3- and I- D Pb 2+ and Na+ E Na+ and I- This is a river in China that became contaminated with Cd 2+ ions. Knowing what you know about precipitation reactions, what do you think could be added to remove the Cd 2+ ions? Slide 76 / 142 Real World Application Cd ions are often removed by adding hydroxides or sulfides to form precipitates move that can be for filtered out of the water Slide 77 / 142 Oxidation-Reduction Reactions Slide 78 / 142 Oxidation/Reduction Reactions Recall that Oxidation/Reduction Reactions involve exchange of electrons between atoms/ions Return to Table of Contents The thermite reaction between iron(iii)oxide and Al generates a lot of heat!
Slide 79 / 142 Oxidation/Reduction Reactions These reactions, often called REDOX reactions, involve a transfer of electrons from one element to another. 4Al(s) + 3O 2(g) 2Al 2O 3 Charge 0 0 +3-2 Slide 80 / 142 Oxidation/Reduction Reactions The electrons lost/gained must be balanced in a REDOX reaction 4Al(s) + 3O 2(g) --> 2Al 2O 3 Each Al loses 3 electrons Oxidation element loses electrons Each O gains 2 electrons Reduction element gains electrons Each Al loses 3 electrons Each O gains 2 electrons 4 x Al x 3e- lost = 12 e- lost 6 x O x 2e- gained = 12 e- gained Slide 81 / 142 Determining Oxidation States In order to determine if a reaction is an oxidation/reduction reaction and which element got oxidized or reduced, one must be able to track the charges (oxidation states) of elements throughout the reaction. Zn + 2H + --> Zn 2+ + H 2 0 +1 +2 0 Oxidation States Since the charges on both the zinc and hydrogen change, this is definitely a redox reaction. Slide 82 / 142 Determining Oxidation States All elements in their standard (neutral) state, have an oxidation state of zero. If the element has a charge listed, this is it's oxidation state. Substance Oxidation State H 2(g) 0 Ca(s) 0 Na + (aq) +1 F - (aq) -1 Slide 83 / 142 Determining Oxidation States If the element is combined with others, the oxidation state will have to be deduced using the periodic table, your knowledge of ionic compounds, and some mathematics. Here are some general guidelines... Rule 1: The charges of all the elements in the compound have to add up to the charge of the compound. Example: ZnO The compound is neutral so... Charge of Zn + Charge of O = 0 Example: NO 3 - Charge of N + charge of O = -1 The compound has a charge of -1 so... Slide 84 / 142 Determining Oxidation States Guideline 1: The charges of all the elements in the compound have to add up to the charge of the compound. Guideline 2: Using your periodic table, find the charge on the anion and use this and what you know to be the charge on the whole compound to find the charge on the cation. Typically, the cation is written first and the anion second. Example: ZnO Charges zinc oxide ZnO? 2-0 2+ + 2- = 0 zinc has a +2 oxidation state!
Slide 85 / 142 Determining Oxidation States Slide 86 / 142 Determining Oxidation States - Another Example: NO 3 Charges N Ox3 - NO 3? -2(3) = -6-1 +5 + -6 = -1 Oxidation States: N = +5 O = -2 Another Example: Cr 2O 2-7 (aq) Charges Cr x 2 O x 7 Cr 2O 2-7? -2(7) =-14-2 +12 + -14 = -2 Since Cr x 2 = +12... the oxidation state of each Cr must be +6! Oxidation states: Cr = +6 O = -2 Slide 87 / 142 Determining Oxidation States Another example: HS - Charges H S HS-? -2-1 +1 + -2 = -1 Move for H = +1, S = -2 Slide 88 / 142 Determining Oxidation States Another Example: N 2O 4 Charges Nx2 Ox4 N 2O 4? -2(4) = -8 0 +8 + -8 = 0 Since Move Nx2 =8, for each N = 4 so... N = +4, O = -2 Slide 89 / 142 18 In which of the following substances would zinc have an oxidation state of 0? A ZnS B Zn C Zn 2+ D ZnSO 4 E ZnCl 2 Slide 90 / 142 19 What is the oxidation state of P in the phosphate ion -- PO 4 3-? A 0 B +1 C +3 D +5 E -3
Slide 91 / 142 Slide 92 / 142 20 What is the oxidation state of Cl in ClO 2-? A 0 B -1 C +1 D +3 E +5 Determining Oxidation States For elements containing three elements, find the oxidation states of the first and last from the periodic table and then find the middle element (usually but not always a transition metal). Example: Na 2S 2O 3 Charges Na x2 Sx2 Ox3 Na 2S 2O 3 +1(2)= +2? -2(3) = -6 0 2 + 4-6 0 Slide 93 / 142 Determining Oxidation States Since Sx2 = 4, each sulfur will have a charge of just +2 so...na =+1, S =+2, and O = -2 Slide 94 / 142 Determining Oxidation States Example: Mg(OH) 2 charges Mg Ox2 Hx2 Mg(OH) 2 +2-2(2)=-4 +1(2)=+2 0 2 + -4 + 2 = 0 Example: KMnO 4 charges K Mn Ox4 KMnO 4 +1? -2(4)=-8 0 move for 1 + 7-8 = 0 All of these charges could be obtained using the periodic table so nothing needed to be figured out! Mg = +2, O = -2, and H = +1 So... K = +1, Mn = +7, and O = -2 Slide 95 / 142 21 What is the oxidation state of each element in K 2TeO 4? A K = +1, Te = +6, O = -2 B K = +2, Te = +4, O = -2 C K = +1, Te = +4, O = -2 D K = +1, Te = +2, O = -2 E K = +1, Te = +8, O = -2 Slide 96 / 142 22 In which of the following substances would S have an oxidation state of +4? A Na 2SO 4 B Na 2SO 3 C Na 2S D S 8 E SO 3
Slide 97 / 142 Exceptions with Determining Oxidation States 1)Peroxides like Na 2O 2 and H 2O 2 Oxygen has an oxidation state of -1 instead of -2 Slide 98 / 142 23 In which of the following would oxygen have an oxidation state of -1? A O 2 B Na 2O C Li 2O 2 D H 2O E None of these 2) Ammonia (NH 3) and ammonium (NH 4+ ) Usually the element with the - charge is written second but that is not the case here. N carries a -3 charge in both instances and H carries a +1 charge. Slide 99 / 142 Find the Oxidation States What are the oxidation states of each element in the following reaction? Slide 100 / 142 Find the Oxidation States What are the oxidation states of each of the elements in the reaction? Fe 2+ (aq) + MnO 4-(aq) + H+ --> H 2O + Mn 2+ + Fe 3+ +2 +7, -2 +1 --> +1, -2 +2 +3 slide for 2H 2O 2 --> 2H 2O + O 2 +1, -1 +1,-2 0 slide for *note that H 2O 2 is a peroxide Key: Ignore coefficients when you find oxidation states! Slide 101 / 142 Slide 102 / 142 24 In the following equation: 2KClO 3 --> 2KCl + 3O 2 25 In the following equation: 2KClO 3 --> 2KCl + 3O 2 the oxidation state of O changes from: the oxidation state of Cl changes from: A -2 --> -2 B -6 --> -2 C -6 --> 0 D -2 --> 0 E -1 --> 0 A -1 --> -1 B 0 --> -1 C +3 --> +5 D + 5 --> -1 E +5 --> 0
Slide 103 / 142 Which species got oxidized/reduced? To determine which species in a reaction got oxidized or reduced, one must know what it means to be oxidized and reduced. Oxidation = Loss of electrons Na --> Na+ + e- 0 --> +1 Notice that an element becomes more + when it gets oxidized. Slide 104 / 142 Which species got oxidized/reduced? Which element got oxidized and which got reduced in the following reaction? 2KClO 3 --> 2KCl + 3O 2 Find Ox. States +1,+5, -2 +1,-1 0 Reduction = Gain of electrons Mg2+ + 2e - --> Mg +2 --> 0 Notice that an element becomes less + when it gets reduced. Chlorine went from +5 --> -1 becoming less + so it must have gained electrons reduced Oxygen went from -2 --> 0 becoming more + so it must have lost electrons oxidized Slide 105 / 142 Which species got oxidized/reduced? Which of the following elements got oxidized and reduced in the following reaction? 2F-(aq) + Cl 2(g) --> 2Cl-(aq) + F2(g) -1 0-1 0 move for Flourine went from -1 to 0 becoming more + meaning electrons were lost = oxidation! Chlorine went from 0 to -1 becoming more - meaning electrons were gained = reduction! Slide 106 / 142 Real World Application An oxidant is a chemical species that wants to be reduced so it causes something else to get oxidized. Free radical species like singlet oxygen are oxidants and not good for you as they will get electrons from molecules in your body that need them! free radical singlet O -----> carotenoid -----> [ ] 2- O + 2e- --> O Anti-oxidants like carotenoids found in veggies have many electrons to lose so they help reduced the radicals so the molecules in your body don't get harmed!!! So...eat your veggies!!! Slide 107 / 142 Slide 108 / 142 26 Which of the following represents a reduction? 27 Which of the following represents an oxidation? A An elements charge going from -3 --> -2 B An elements charge going from -2 -->-3 C An elements charge going from 0 --> +2 D An elements charge going from +1 --> +3 E None of these A Al 3+ (aq) --> Al(s) B F 2(g) --> 2F-(aq) C Mn 7+ --> Mn 2+ D Fe 2+ (aq) --> Fe 3+ (aq) E O-(aq) --> O 2- (aq)
Slide 109 / 142 28 In which of the following equations does O get oxidized? Slide 110 / 142 29 Which of the following is NOT an oxidation/reduction reaction? A 2H 2O 2 -- 2H 2O + O 2 B 2H 2O --> 2H 2 + O 2 C CH 4 + 2O 2 --> CO 2 + 2H 2O D 3Fe + 3O 2 --> 2Fe 2O 3 E None of these A Ca + 2H+ --> Ca 2+ + H 2 B H 2 + Cl 2 -->2HCl C 4Al + 3O 2 --> 2Al 2O 3 D CaO + CO 2 --> CaCO 3 E Mg 3N 2 --> 3Mg + N 2 Slide 111 / 142 Slide 112 / 142 Real World Application Chromium metal is used as rust resistant coating over steel as shown on the motorcycle. This is accomplished by reducing chromium ions. What element do you think gets oxidized at the natural gas burning power plant to provide the energy so chromium can get reduced? Types of Oxidation-Reduction Reactions Cr 3+ + 3e- --> Cr(s) C gets oxidized and releases a lot of energy which is used to generate the potential so electrons will move through the wire and reduce the Cr 3+ ions. CH Slide 4 + for 2OAnswer 2 --> CO 2 + 2H 2O -4 +4 Return to Table of Contents Slide 113 / 142 Slide 114 / 142 Types of Oxidation/Reduction Reactions Combination/Synthesis Reactions There are essentially four types of Redox reactions: 1. Synthesis or Combination - two or more substances combine 2Mg(s) + O 2(g) --> 2MgO(s) 2. Decomposition - a substance breaks into two or more compounds 2LiClO 3(s) --> 2LiCl(s) + 3O 2(g) 3. Combustion - a substance reacts with oxygen. C(s) + O2(g) --> CO 2(g) CH 4(g) + 2O 2(g) --> CO 2(g) + 2H 2O(g) 4. Disproportionation - the same material gets both oxidized and reduced Hg 2Cl 2 Hg + HgCl 2 Two or more substances react to form one product. Mg O 2 MgO Examples: 2 Mg (s) + O2 (g) 2 MgO (s) N2 (g) + 3 H2 (g) 2 NH3 (g) C3H6 (g) + Br2 (l) C3H6Br2 (l)
Slide 115 / 142 30 Which of the following is a combination reaction? Slide 116 / 142 Decomposition Reactions A H2O --> H2 +O2 B Na + Cl2 --> NaCl C AgNO3 + BaSO4 --> Ag2SO4 + Ba(NO3)2 One substance breaks down into two or more substances. # + 2 H2O # O2 + 2 H2 D C3H8 + O2 --> H2O + CO2 Examples: E CaCO3 --> CaO + CO2 CaCO3 (s) CaO (s) + CO2 (g) 2 KClO3 (s) # 2 KCl (s) + 3 O2 (g) 2 NaN3 (s) 2 Na (s) + 3 N2 (g) Slide 117 / 142 Slide 118 / 142 31 Which of the following is a decomposition reaction? Combustion Reactions A H2O --> H2 +O2 B Na + Cl2 --> NaCl C AgNO3 + BaSO4 --> Ag2SO4 + Ba(NO3)2 D C3H8 + O2 --> H2O + CO2 E Ca2+ (aq) + SO 2-4 (aq) --> CaSO(s) These are generally rapid reactions that produce a flame. Most often involve hydrocarbons reacting with oxygen in the air. O 2 is always one of the reactants. Examples: CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g) C3H8 (g) + 5 O2 (g) 3 CO2 (g) + 4 H2O (g) Slide 119 / 142 Slide 120 / 142 Combustion Reactions 32 Which of the following is a combustion reaction? Note: substances other than hydrocarbons may also undergo combustion: A H2O --> H2 +O2 B Na + Cl2 --> NaCl Mg (s) + O2 (g) ---> MgO (s) N2 (g) + 2 O2 (g) ---> 2 NO2 (g) These last two may also be classified as combination reactions. C D E AgNO3 + BaSO4 --> Ag2SO4 + Ba(NO3)2 C3H8 + O2 --> H2O + CO2 Ca2+ + SO 4 2- --> CaSO 4(s)
Slide 121 / 142 Combustion Reactions Combustion reactions are easily identified by oxygen as a reactant. However, the products of a combustion reaction may vary depending on how much oxygen is available. Slide 122 / 142 Disproportionation Reactions The same element gets both oxidized and reduced. Hg 2Cl 2 --> 2Hg + HgCl 2 Oxid. States: +1, -1 0 +2, -1 Complete combustion Incomplete combustion Hg gets both oxidized (+1 -->+2) and reduced (+1 -->0) products are carbon dioxide and water products are carbon monoxide and water Slide 123 / 142 Disproportionation Reactions Slide 124 / 142 33 Which of the following would be a disproportionation reacti Is the following a disproportionation reaction and if so, what element is getting both oxidized and reduced? Cl 2 + 6 OH 5 Cl + ClO 3 + 3 H 2O Oxid.States 0-1,+1-1 +5,-2 +1,-2 A CO C + CO 2 B CaCO 3 --> CaO + CO 2 C H 2O --> H 2 + O 2 D H 2 + F 2 --> 2HF E none of these move for It is! Cl is the element that gets both oxidized and reduced Slide 125 / 142 Slide 126 / 142 34 Which element gets both oxidized and reduced in the following disproportionation reaction? NaOH + Cl 2 --> NaCl + NaClO + H 2O Acid-Base Reactions A Na B Cl C O D H E This is NOT a disproportionation reaction Return to Table of Contents
Slide 127 / 142 Acid/Base Reactions Slide 128 / 142 Bronsted-Lowry Definition of Acids and Bases Acid = H+ ion donor Base = H+ acceptor Soda pop contains two common weak acids: phosphoric acid (H 3PO 4) and carbonic acid (H 2CO 3) H+ acceptor H+ donor Slide 129 / 142 Lewis Definition of Acids and Bases Slide 130 / 142 Acid/Base Reactions Acid = electron pair acceptor Base = electron pair donor Bronsted/Lowry Acid/Base reactions involve the transfer of H+ ions from one an acid (H+ donor) to a base (H+ acceptor) Example: HC 2H 3O 2(aq) + CO 3 2- (aq) --> HCO 3-(aq) + C 2H 3O 2-(aq) ** unless otherwise noted, we will be using the bronsted/lowry definition of acids and bases throughout the rest of the presentation. HC 2H 3O 2(aq) gave away it's H+ = acid CO 3 2- (aq) accepted an H+ = base Slide 131 / 142 Acid/Base Reactions Identify the acid and base in the following reaction: CN- + H2O --> HCN + OH- Slide 132 / 142 Acid/Base Reactions Identify the acid and base in the following reaction: HCO 3- + HF --> F- + H 2CO 3 CN- accepted an H+ so it is a base H2O donated an H+ so it is an acid move for HCO3- accepted an H+ so it was a base HF donated an H+ so it was an acid
Slide 133 / 142 Neutralization Reactions Neutralization reactions are a special type of acid/base reaction in which an acid and base react to produce water. Example: HF + OH- --> H 2O + F- Slide 134 / 142 35 Which of the following acid/base reactions represent a neutralization reaction? A H+ + CN- --> HCN B HNO 2 + OH- --> H 2O + NO 2- C HCN + NH 3 --> NH 4+ + CN- D HCO 3- + H 2O --> CO 3 2- + H 3O+ E none of these Slide 135 / 142 Slide 136 / 142 Real World Application HC 2H 3O 2(aq) + HCO 3-(aq) --> C 2H 3O 2-(aq) + CO 2(g) + H 2O(l) Identifying Reaction Types The classic childhood reaction of vinegar (HC 2H 3O 2) and baking soda (HCO 3-) is an acid/base reaction. Which molecule is the conjugate base of acetic acid (HC 2H 3O 2)? C 2H 3O 2- Return to Table of Contents Slide 137 / 142 Identifying what kind of reaction it is? One can determine the type of chemical reaction by following some basic guidelines... Slide 138 / 142 Identifying what kind of reaction it is? What kind of reaction is the following? C 4H 8(s) + O 2(g) --> CO 2(g) + H 2O(g) 1) Are you forming a precipitate? Look for the formation of an insoluble solid 2) Check to see if H+ ions are being transferred? If so, you've got an acid/base reaction 1) Is there a precipitate? 2) Is there a transfer of H+ ions? 3) Check oxidation states... 3) Check oxidation states If they change, you've got an oxidation/reduction reaction
Slide 139 / 142 Identifying what kind of reaction it is? What kind of reaction is the following? C 4H 8(s) + O 2(g) --> CO 2(g) + H 2O(g) 1) Is there a precipitate? No - So... not a precipitation reaction 2) Is there a transfer of H+ ions? No - So...not an acid/base reaction 3) Check oxidation states... C 4H 8(s) + O 2(g) --> CO 2(g) + H 2O(g) -2,+1 0 +4,-2 +1,-2 Carbon changes from -2 --> +4 and Oxygen changes from 0 -->-2. Oxidation states are definitely changing = REDOX!!! Slide 140 / 142 36 Which of the following would be an example of an oxidation/reduction reaction? A CH 3COOH + NH 3 --> NH 4+ + CH 3COO- B AlCl 3(s) --> Al 3+ (aq) + 3Cl-(aq) C 2Ag+(aq) + Cu(s) --> Cu 2+ (aq) + 2Ag(s) D H+(aq) + OH-(aq) --> H2O(l) E Zn 2+ (aq) + CO 3 2- (aq) --> ZnCO 3(s) Slide 141 / 142 Slide 142 / 142 Identifying what kind of reaction it is? What type of chemical reaction is the following? Mg 2+ (aq) + 2OH-(aq) --> Mg(OH) 2(s) 37 Which of the following is NOT an acid/base reaction? A H 2O + CN- --> OH- + HCN B 2CuO -->2Cu + O 2 C NH 3 + HSO 4- --> NH 4+ + SO 4 2- D H+ + OH- --> H 2O E All of these are acid/base reactions 1. Are you forming a precipitate? Yes... Precipitation move for