New Jersey Center for Teaching and Learning AP Chemistry - PDF document

Slide 1 / 83 Slide 2 / 83 New Jersey Center for Teaching and Learning AP Chemistry 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 Unit 3: Presentation E permission of the owners. NJCTL maintains its website for the convenience of teachers who wish to Redox Reactions 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 www.njctl.org Slide 3 / 83 Slide 4 / 83 REDOX Reactions 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 Photosynthesis is a classic REDOX reaction where electrons ion. are transferred from water to carbon dioxide to create a new Cu(s) got oxidized sugar molecule. Ag + (aq) got reduced Slide 5 / 83 Slide 6 / 83 Oxidation and Reduction Oxidation States In order to determine whether a substance got oxidized or reduced Oxidation Reduction in a reaction, the oxidation state of each species must be known. Loses electrons (LEO) gains electrons (GER) If the substance is found in its neutral standard state, its oxidation state increases oxidation state decreases oxidation state will be zero. electrons are product electrons are reactant Na (s) = 0 or F 2(g) = 0 or C (graphite) = 0 Na (s) --> Na +(aq) + e - Mg 2+(aq) + 2e - --> Mg (s) If the substance is a molecular compound made of more than one element, the sum of the oxidation states must equal 0 C O 2 The less electronegative 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 Slide 8 / 83 Oxidation States Oxidation States For ionic species, the sum of the oxidation states must equal Peroxides and hydrides the charge on the ion. S O 32- In a peroxide (H 2 O 2 or Na 2 O 2 ) O carries an oxidation state of -1. +4 -2 In a hydride (NaH or CaH 2 ), H carries an oxidation state of -1. 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 9 / 83 Slide 10 / 83 2 Which of the substances found in the reaction below 1 Oxidation/Reduction reactions study the transfer of would contain an element with an ________ between atoms and molecules. oxidation number = 0? 10Au (s) + 36H +(aq) + 6NO 3-(aq) --> 3N 2(g) + 18H 2 O (l) + 10Au 3+(aq) A protons B neutrons A Au C H+ ions B HNO 3 D OH- ions C Au and N 2 E electrons Au and H 2 O D N 2 and Au 3+ E Slide 11 / 83 Slide 12 / 83 3 In the substance glucose (C 6 H 12 O 6 ), the sum total of 4 In the compound IBr, which element would be the the oxidation states must equal _____. most electronegative and what would it's oxidation state be? A 0 A I, -1 B +1 B Br, -1 I Br The sum total of the number of valence electrons C C I, 0 present in each element Br, 0 D +3 D Br, +1 E E 24

Slide 13 / 83 Slide 14 / 83 5 The oxalate ion, C 2 O 42- , is one of the common 6 The polyatomic ion cyanide (CN-) is toxic and used components of kidney stones! Which is the more in the mining of gold in America's desert southwest. electronegative atom in the ion and what is it's Which of the following could be a correct set of oxidation state? oxidation states for C and N in the ion? A C, +4 A C = +4, N = -3 B C, -2 B C = +4, N = 0 C C, -4 C C = +2, N = -3 O, -2 D C = 0, N = +1 D O, -4 E E C = -3, N = +4 Slide 15 / 83 Slide 16 / 83 7 What is the oxidation state of O in the compound 8 What would be the oxidation state of the fluorine N 2 O (laughing gas) and what would be the total atom in the compound OF 2 and what would be the negative charge from all the oxygens? total negative charge from the Flourines? A -1, -1 A -2, -2 N N O B 0, -1 B -1, 0 C -1, -2 C -2, 0 -1, -3 D D -2, -4 E -1, 0 -2, -4 E Slide 17 / 83 Slide 18 / 83 10 What is the oxidation number of each oxygen atom in the compound MnO 2 ? A -2 -1 B C 0 D +1 E +2

Slide 19 / 83 Slide 20 / 83 11 What is the oxidation state of S in the S 2 O 32- ion? 12 What is the oxidation state of each atom in CaC 2 O 4 ? The S 2 O 32- ion can do great harm to metals like iron. A Ca = 0, C = +2, O = -2 A -2 B Ca = +2, C = +2, O = -2 B +2 C Ca = +4, C = +4, O =-2 Ca = +2, C = +3, O = -2 D C -1 Ca = +2, C = +4, O = -2 E D +4 E 0 Slide 21 / 83 Slide 22 / 83 13 In 2004, Coca cola had to recall their Dasani brand 14 Chloroform, CHCl 3 , has wide uses. It is used as an water because of the presence of the bromate ion in the anesthetic, a refrigerant, and in the making of teflon. drinking water. What would be the oxidation state of all What is the oxidation state of carbon in chloroform? atoms in CuBrO 3 ? A -2 A Cu = +2, Br = -1, O = -2 B -1 B Cu = +1, Br = +3, O = -2 0 C Cu = +2, Br = +4, O = -2 C Cu = +1, Br = +5, O =-2 D +2 D Cu = 0, Br = +6, O =-2 E E -3 Slide 23 / 83 Slide 24 / 83 REDOX Reactions 15 In which of the following compounds would oxygen have an oxidation state of -1? To determine which substances got oxidized or reduced, look at the change in the substances oxidation state. A Li 2 O 2 H +(aq) + I O 3-(aq) + F -(g) --> I 2(s) + F 2 (aq) + H 2 O (l) B Mg(OH) 2 +1 +5 -2 -1 0 0 +1 -2 C CH 3 OH IO 3- (aq) got reduced = +5 --> 0 D O 2 F 2 (g) got oxidized = 0 --> -1 E Li 2 O

Slide 25 / 83 Slide 26 / 83 16 Which of the following represents a reduction? 17 Which of the following represents an oxidation? A Al 3+(aq) --> Al (s) A An elements charge going from -3 --> -2 B F 2(g) --> 2F -(aq) B An elements charge going from -2 -->-3 C Mn 7+ --> Mn 2+ C An elements charge going from 0 --> +2 D Fe 2+(aq) --> Fe 3+(aq) D An elements charge going from +1 --> +3 None of these O -(aq) --> O 2-(aq) E E Slide 27 / 83 Slide 28 / 83 18 In which of the following equations does O get 19 Which of the following is NOT an oxidation/reduction reaction? oxidized? A 2H 2 O 2 -- 2H 2 O + O 2 A Ca + 2H+ --> Ca 2+ + H 2 B 2H 2 O --> 2H 2 + O 2 B H 2 + Cl 2 -->2HCl C CH 4 + 2O 2 --> CO 2 + 2H 2 O C 4Al + 3O 2 --> 2Al 2 O 3 D 3Fe + 3O 2 --> 2Fe 2 O 3 D CaO + CO 2 --> CaCO 3 E A and B E Mg 3 N 2 --> 3Mg + N 2 Slide 29 / 83 Slide 30 / 83 Oxidizing and Reducing Agents 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) Any substance that gets oxidized is called a reducing agent or reducer becomes the electrons lost will be gained by another species. A Cr 2 O 72- gets oxidized to Cr 3+ Any substance that gets reduced is called an oxidizing agent B Fe 2+ gets reduced to Fe 3+ or oxidizer becomes the electrons gained will be lost by C H + gets reduced to H 2 O another species. Cr 2 O 72- gets oxidized to H 2 O D Remember: Reducing Agents are Oxidized Fe 2+ gets oxidized to Fe 3+ E Oxidation Agents are Reduced.

Slide 31 / 83 Slide 32 / 83 Oxidizing and Reducing Agents 21 Identify the oxidizing agent in the following reaction. Good reducing agent must lose electrons easily. Neutral metals Al (s) + 6HCl (aq) --> AlCl 3(aq) + H 2(g) or substances with low ionization energies fit the bill. For example: Na, I - , Fe 2+ A Al B AlCl 3 C HCl Good oxidizing agents must gain electrons easily. Neutral or positive non-metals or highly positive metals fit the bill here. D H 2 For example: MnO 4- , CrO 42- , F 2 , O 2, HNO 3 Slide 33 / 83 Slide 34 / 83 22 Which substance is oxidized in the following 23 Which substance is the reducing agent below? reaction? (First, assign oxidation numbers.) Cu + S ➝ CuS Cu + S ➝ CuS A Cu A Cu B S B S C Cu and S C Cu and S D CuS D CuS E This is not a redox reaction. E This is not a redox reaction. Slide 35 / 83 Slide 36 / 83 24 Which substance is oxidized in the following 25 Which substance is the reducing agent? reaction? (First, assign oxidation numbers.) 3 K + Al(NO 3 ) 3 ➝ Al + 3 KNO 3 Ca + Fe 3+ ➝ Ca 2+ + Fe A Ca A K B Fe 3+ B Al(NO 3 ) 3 C Ca 2+ C KNO 3 D Fe D This is not a redox reaction. E This is not a redox reaction.