Slide 1 / 83 New Jersey Center for Teaching and Learning Progressive Science Initiative This material is made freely available at www.njctl.org and is intended for the non-commercial use of students and teachers. These materials may not be used for any commercial purpose without the written permission of the owners. NJCTL maintains its website for the convenience of teachers who wish to make their work available to other teachers, participate in a virtual professional learning community, and/or provide access to course materials to parents, students and others. Click to go to website: www.njctl.org Slide 2 / 83 AP Chemistry Unit 3: Presentation E Redox Reactions www.njctl.org Slide 3 / 83 REDOX Reactions Photosynthesis is a classic REDOX reaction where electrons are transferred from water to carbon dioxide to create a new sugar molecule.
Slide 4 / 83 Oxidation and Reduction REDOX reactions involve the transfer of electrons from one species to another. The substance that gains electrons is said to be reduced while the substance that loses electrons is said to be oxidized . Cu (s) + Ag +(aq) --> Cu +(aq) + Ag (s) In this reaction, a copper atom loses an electron to a silver ion. Cu(s) got oxidized Ag + (aq) got reduced Slide 5 / 83 Oxidation and Reduction Oxidation Reduction Loses electrons (LEO) gains electrons (GER) oxidation state increases oxidation state decreases electrons are product electrons are reactant Na (s) --> Na +(aq) + e - Mg 2+(aq) + 2e - --> Mg (s) Slide 6 / 83 Oxidation States In order to determine whether a substance got oxidized or reduced in a reaction, the oxidation state of each species must be known. If the substance is found in its neutral standard state, its oxidation state will be zero. Na (s) = 0 or F 2(g) = 0 or C (graphite) = 0 If the substance is a molecular compound made of more than one element, the sum of the oxidation states must equal 0 The less electronegative C O 2 The more electronegative of the two receives the + -2 of the two receives a +4 charge necessary to charge equivalent to it's cancel out the negative normal ionic charge. charge
Slide 7 / 83 Oxidation States For ionic species, the sum of the oxidation states must equal the charge on the ion. S O 32- +4 -2 For ionic compounds, first separate the compound into its ions, then determine charge on each element. Mg Cr 2 O 7 +2 -2 Cr 2 O 7 + 6 -2 Slide 8 / 83 Oxidation States Peroxides and hydrides In a peroxide (H 2 O 2 or Na 2 O 2 ) O carries an oxidation state of -1. In a hydride (NaH or CaH 2 ), H carries an oxidation state of -1. Slide 9 / 83 1 Oxidation/Reduction reactions study the transfer of ________ between atoms and molecules. A protons B neutrons C H+ ions D OH- ions E electrons
Slide 10 / 83 2 Which of the substances found in the reaction below would contain an element with an oxidation number = 0? 10Au (s) + 36H +(aq) + 6NO 3-(aq) --> 3N 2(g) + 18H 2 O (l) + 10Au 3+(aq) A Au B HNO 3 C Au and N 2 Au and H 2 O D N 2 and Au 3+ E Slide 11 / 83 3 In the substance glucose (C 6 H 12 O 6 ), the sum total of the oxidation states must equal _____. A 0 B +1 The sum total of the number of valence electrons C present in each element D +3 E 24 Slide 12 / 83 4 In the compound IBr, which element would be the most electronegative and what would it's oxidation state be? A I, -1 B Br, -1 I Br C I, 0 D Br, 0 E Br, +1
Slide 13 / 83 5 The oxalate ion, C 2 O 42- , is one of the common components of kidney stones! Which is the more electronegative atom in the ion and what is it's oxidation state? A C, +4 B C, -2 C C, -4 O, -2 D E O, -4 Slide 14 / 83 6 The polyatomic ion cyanide (CN-) is toxic and used in the mining of gold in America's desert southwest. Which of the following could be a correct set of oxidation states for C and N in the ion? A C = +4, N = -3 B C = +4, N = 0 C C = +2, N = -3 D C = 0, N = +1 E C = -3, N = +4 Slide 15 / 83 7 What is the oxidation state of O in the compound N 2 O (laughing gas) and what would be the total negative charge from all the oxygens? A -2, -2 N N O B -1, 0 C -2, 0 D -2, -4 -2, -4 E
Slide 16 / 83 8 What would be the oxidation state of the fluorine atom in the compound OF 2 and what would be the total negative charge from the Flourines? A -1, -1 B 0, -1 C -1, -2 -1, -3 D E -1, 0 Slide 17 / 83 Slide 18 / 83 10 What is the oxidation number of each oxygen atom in the compound MnO 2 ? A -2 B -1 C 0 D +1 E +2
Slide 19 / 83 11 What is the oxidation state of S in the S 2 O 32- ion? The S 2 O 32- ion can do great harm to metals like iron. A -2 B +2 C -1 D +4 E 0 Slide 20 / 83 12 What is the oxidation state of each atom in CaC 2 O 4 ? A Ca = 0, C = +2, O = -2 B Ca = +2, C = +2, O = -2 C Ca = +4, C = +4, O =-2 Ca = +2, C = +3, O = -2 D Ca = +2, C = +4, O = -2 E Slide 21 / 83 13 In 2004, Coca cola had to recall their Dasani brand water because of the presence of the bromate ion in the drinking water. What would be the oxidation state of all atoms in CuBrO 3 ? A Cu = +2, Br = -1, O = -2 B Cu = +1, Br = +3, O = -2 C Cu = +2, Br = +4, O = -2 Cu = +1, Br = +5, O =-2 D E Cu = 0, Br = +6, O =-2
Slide 22 / 83 14 Chloroform, CHCl 3 , has wide uses. It is used as an anesthetic, a refrigerant, and in the making of teflon. What is the oxidation state of carbon in chloroform? A -2 B -1 0 C +2 D E -3 Slide 23 / 83 15 In which of the following compounds would oxygen have an oxidation state of -1? A Li 2 O 2 B Mg(OH) 2 C CH 3 OH D O 2 E Li 2 O Slide 24 / 83 REDOX Reactions To determine which substances got oxidized or reduced, look at the change in the substances oxidation state. H +(aq) + I O 3-(aq) + F -(g) --> I 2(s) + F 2 (aq) + H 2 O (l) +1 +5 -2 -1 0 0 +1 -2 IO 3- (aq) got reduced = +5 --> 0 F 2 (g) got oxidized = 0 --> -1
Slide 25 / 83 16 Which of the following represents a reduction? A An elements charge going from -3 --> -2 An elements charge going from -2 -->-3 B An elements charge going from 0 --> +2 C An elements charge going from +1 --> +3 D None of these E Slide 26 / 83 17 Which of the following represents an oxidation? A Al 3+(aq) --> Al (s) B F 2(g) --> 2F -(aq) C Mn 7+ --> Mn 2+ D Fe 2+(aq) --> Fe 3+(aq) O -(aq) --> O 2-(aq) E Slide 27 / 83 18 In which of the following equations does O get oxidized? A 2H 2 O 2 -- 2H 2 O + O 2 B 2H 2 O --> 2H 2 + O 2 C CH 4 + 2O 2 --> CO 2 + 2H 2 O D 3Fe + 3O 2 --> 2Fe 2 O 3 E A and B
Slide 28 / 83 19 Which of the following is NOT an oxidation/reduction reaction? A Ca + 2H+ --> Ca 2+ + H 2 B H 2 + Cl 2 -->2HCl C 4Al + 3O 2 --> 2Al 2 O 3 D CaO + CO 2 --> CaCO 3 Mg 3 N 2 --> 3Mg + N 2 E Slide 29 / 83 20 Which of the following would be TRUE regarding the reaction that occurs below. Cr 2 O 72-(aq) + 14H +(aq) + 6Fe 2+(aq) --> 2Cr 3+(aq) + 7H 2 O (l) + 6Fe 3+(aq) A Cr 2 O 72- gets oxidized to Cr 3+ B Fe 2+ gets reduced to Fe 3+ C H + gets reduced to H 2 O Cr 2 O 72- gets oxidized to H 2 O D Fe 2+ gets oxidized to Fe 3+ E Slide 30 / 83 Oxidizing and Reducing Agents Any substance that gets oxidized is called a reducing agent or reducer becomes the electrons lost will be gained by another species. Any substance that gets reduced is called an oxidizing agent or oxidizer becomes the electrons gained will be lost by another species. Remember: Reducing Agents are Oxidized Oxidation Agents are Reduced.
Slide 31 / 83 Oxidizing and Reducing Agents Good reducing agent must lose electrons easily. Neutral metals or substances with low ionization energies fit the bill. For example: Na, I - , Fe 2+ Good oxidizing agents must gain electrons easily. Neutral or positive non-metals or highly positive metals fit the bill here. For example: MnO 4- , CrO 42- , F 2 , O 2, HNO 3 Slide 32 / 83 21 Identify the oxidizing agent in the following reaction. Al (s) + 6HCl (aq) --> AlCl 3(aq) + H 2(g) A Al B AlCl 3 C HCl D H 2 Slide 33 / 83 22 Which substance is oxidized in the following reaction? (First, assign oxidation numbers.) Cu + S ➝ CuS A Cu B S C Cu and S D CuS E This is not a redox reaction.
Slide 34 / 83 23 Which substance is the reducing agent below? Cu + S ➝ CuS A Cu B S C Cu and S D CuS E This is not a redox reaction. Slide 35 / 83 24 Which substance is oxidized in the following reaction? (First, assign oxidation numbers.) Ca + Fe 3+ ➝ Ca 2+ + Fe A Ca B Fe 3+ C Ca 2+ D Fe E This is not a redox reaction. Slide 36 / 83 25 Which substance is the reducing agent? 3 K + Al(NO 3 ) 3 ➝ Al + 3 KNO 3 A K B Al(NO 3 ) 3 C KNO 3 D This is not a redox reaction.
Slide 37 / 83 26 Which of the following would make the best oxidizing agent? A H 2 O B IO 3- C IO 2- D I 2 E I - Slide 38 / 83 27 Which of the following would make the best reducing agent? A F 2(g) B Cl 2(g) C K (s) D Al (s) E C (s) Slide 39 / 83 28 Good oxidizing agents will have low ionization energies. Yes No
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