Chapter 21- Electrochemistry Reduction-Oxidation or REDOX chemistry.

Slides:



Advertisements
Similar presentations
Oxidation-reduction reactions
Advertisements

Recap Precipitation Reactions: ions combine to form insoluble products Neutralization Reactions: H + ions and OH - ions combine to form H 2 O Next: Oxidation-Reduction.
Aim: Assigning oxidation numbers
1 Chapter 5 Chemical Reactions 5.3 Oxidation-Reduction Reactions.
Advanced Higher Chemistry Unit 1 Oxidation states of the transition metals.
Redox Reactions. What is redox? Redox reactions involve a transfer of electrons. Oxidation – involves losing electrons (increase in oxidation number)
Redox Reactions What is oxidation? What is reduction?
Oxidation Reduction Reactions. Oxidation Reduction Reactions… are chemical changes that occur when electrons are transferred between reactants.
Introduction to Oxidation and Reduction
Unit 6 Oxidation/Reduction and Electrochemistry
Objectives Assign oxidation numbers to reactant and product species. Define oxidation and reduction. Explain what an oxidation-reduction reaction (redox.
 Oxidation Reduction Reaction (Redox): A reaction in which electrons are transferred from one substance to another.
REDOX Reactions Oxidation – Reduction.
Redox Reactions: Oxidation and Reduction. I. ELECTRON TRANSFER AND REDOX REACTIONS.
UNIT 6: ELECTROCHEMISTRY. REDOX REACTIONS Redox is short for ‘oxidation and reduction’ Oxidation refers to substances that combine with oxygen Iron rusting,
REDOX Oxidation and Reduction Chapters 20 and 21.
Chapter 20 Oxidation-Reduction Reactions Anything in black letters = write it in your notes (‘knowts’)
1 Oxidation- Reduction Chapter 16 Tro, 2 nd ed. 1.1.
REDOX AND ELECTROCHEMISTRY Oxidation Number A. Convenient way for keeping track of the number of electrons transferred in a chemical reaction A. Convenient.
Oxidation and Reduction ……………………….. Objectives Oxidised, reduced Definition- oxidising/reducing agent, oxidant/reductant Rules of oxidation number Refer.
Define oxidation and reduction. Determine oxidation numbers for atoms. Identify the oxidizing agent, the reducing agent. Distinguish between redox and.
Electrochemistry.
Redox and Electrochemistry. Redox Reactions Reduction – Oxidation reactions Involve the transfer of electrons from one substance to another The oxidation.
Electrochemistry Chemistry 30 Unit 2 the transfer of electrons in chemical reactions.
Redox Reactions Chapter 18 + O 2 . Oxidation-Reduction (Redox) Reactions “redox” reactions: rxns in which electrons are transferred from one species.
REDOX electrochemistry. Spontaneous redox reactions can transfer energy –Electrons (electricity) –Heat Non-spontaneous redox reactions can be made to.
Oxidation Numbers. The Rules All free uncombined elements have an oxidation number of zero (In diatomic elements like F 2, each fluorine’s oxidation number.
Oxidation Numbers and Redox Reactions Section 7.2.
Oxidation, Reduction and Electrochemistry
Redox & Electrochemistry What’s the point ? Electrical production (batteries, fuel cells) REDOX reactions are important in … Purifying metals (e.g. Al,
The Finish Line is in site… Electrochemistry. Oxidation Numbers OBJECTIVES Determine the oxidation number of an atom of any element in a pure substance.
Unit #3: Electrochemistry Lesson 1: Oxidation and Reduction.
Introduction to Redox Mrs. Kay Chemistry 12 Chapter 18 Pages:
Redox Reactions Reactants: Zn + I 2 Product: Zn I 2.
Copper oxidizes in air to form the green patina.
Unit 11: Redox Oxidation numbers. What is an Oxidation number? Oxidation numbers are assigned to an atom in a molecule based on the distribution of electrons.
CHAPTER 20 “Oxidation-Reduction Reactions” LEO SAYS GER Pre-AP Chemistry Charles Page High School Modified Stephen L. Cotton.
Chemistry Chapter 19 Oxidation and Reduction 1. Oxidation-Reduction Involves movement of electrons Oxidation: ▫Effective loss of electrons Reduction:
Chemical Reactions Non-Redox Reactions (Double Replacement) Redox Reactions Precipitation 2 solutions  Solid ppt Neutralization Acid + Base  salt +
1 Chapter 20 Oxidation-Reduction Reactions (Redox Reactions)
REDOX REACTIONS. REDUCTION Previously: What happened to oxygen when it reacted – During reactions oxygen would take on electrons Now: When any element.
Oxidation and Reduction Reactions (called “redox”) OBJECTIVES Define the terms oxidation and reduction.
REDOX reactions Oxidation and Reduction. Redox chemistry The study of oxidation and reduction reactions Oxidation and reduction reactions involve the.
The Finish Line is in site…
Redox Reactions.
REDOX electrochemistry.
Oxidation & Reduction Reactions
Oxidation-Reduction Reactions
Oxidation and Reduction Reactions
Redox and Assigning Oxidation Numbers
Redox Rules to Learn For Ionic and Covalent bonds
Solution Chemistry RedOx Reactions.
Oxidation Reduction Chemisty: Redox Chemistry
Redox Reactions Chapter 18 + O2 .
Unit 7: Redox & Electrochemistry
Oxidation-reduction reactions & electrochemistry
Oxidation Numbers.
Chapter 19.1 oxidation number or oxidation state –
Also called Reduction-Oxidation Reactions
Redox Reactions Chapter 18 + O2 .
“Redox” is the combination of the two words Lesson 1
Introduction to Electrochemistry
Chapter 20: LEO the lion goes GER
Unit 6 – Redox Reactions and Electrochemistry
Unit 13: Electrochemistry
Unit 11: Classification of Chemical Reactions
Oxidation Numbers.
Unit 11: Classification of Chemical Reactions
Oxidation and Reduction
Unit 6: Electrochemistry
Presentation transcript:

Chapter 21- Electrochemistry Reduction-Oxidation or REDOX chemistry

21-1: Introduction to Electrochemistry Background: In Chemistry 11 we saw many Single Replacement reactions, such as: Background: In Chemistry 11 we saw many Single Replacement reactions, such as: Mg (s) + 2HCl (aq) ssd MgCl 2(aq) + H 2(g) Mg (s) + 2HCl (aq) ssd MgCl 2(aq) + H 2(g) In fact, this is a two part “REDOX” reaction: In fact, this is a two part “REDOX” reaction:

1) Mg (s) ssd Mg 2+ (aq) + 2 e — Mg (s) has LOST two Electrons during an OXIDATION reaction (* LEO = loss of electrons is oxidation) 2) 2H + (aq) + 2 e — ssd H 2 (g) The H + ions have GAINED two Electrons during a REDUCTION reaction (*GER = gain of electrons is reduction) Note: The Cl — ions in the original reaction did not participate and are SPECTATOR ions

Background…. Cont’d Oxidation and Reduction reactions occur simultaneously… every electron lost in the oxidation is gained in the reduction. Oxidation and Reduction reactions occur simultaneously… every electron lost in the oxidation is gained in the reduction. As each of these reactions is one-half of the overall reaction, we call them… HALF- REACTIONS! As each of these reactions is one-half of the overall reaction, we call them… HALF- REACTIONS!

Back to our example: Back to our example: 1) Mg (s) sd Mg 2+ (aq) + 2 e — OXIDATION 2) 2H + (aq) + 2 e — sd H 2 (g) REDUCTION Mg (s) + 2H + (aq) sd Mg 2+ (aq) + H 2 (g) These two reactions can be combined to yield the overall NET reaction. Mg gets oxidized, but CAUSES the reduction of H +, and Mg is called the REDUCING AGENT H + gets reduced, but CAUSES the oxidation of Mg and H + is called the OXIDIZING AGENT

The Reducing Agent gets oxidized and the Oxidizing Agent gets reduced

2+

Another Example 3CuCl 2(aq) +2Al (s) ssd 2AlCl 3(aq) + 3Cu (s) 3CuCl 2(aq) +2Al (s) ssd 2AlCl 3(aq) + 3Cu (s) Two half reactions: Two half reactions: 1) Cu 2+ (aq) + 2e — ssd Cu (s) 1) Cu 2+ (aq) + 2e — ssd Cu (s) Cu 2+ ion GAINS 2 electrons and is Cu 2+ ion GAINS 2 electrons and is REDUCED REDUCED 2) Al (s) ssd Al 3+ (aq) + 3e — 2) Al (s) ssd Al 3+ (aq) + 3e — Aluminum atom LOSES 3 electrons and is Aluminum atom LOSES 3 electrons and is OXIDIZED OXIDIZED

Cu 2+ ion is the OXIDIZING AGENT and gets REDUCED Cu 2+ ion is the OXIDIZING AGENT and gets REDUCED Al atom is the REDUCING AGENT and gets OXIDIZED Al atom is the REDUCING AGENT and gets OXIDIZED

REMEMBER: LEO the Lion says GER REMEMBER: LEO the Lion says GER -- LEO= Loss of Electrons is Oxidation -- LEO= Loss of Electrons is Oxidation -- GER= Gain of Electrons is Reduction -- GER= Gain of Electrons is Reduction

21-2 Oxidation Numbers Oxidation and reduction can be explained in terms of the loss and gain of electrons. Oxidation numbers are used to help keep track of electrons in chemical reactions Oxidation and reduction can be explained in terms of the loss and gain of electrons. Oxidation numbers are used to help keep track of electrons in chemical reactions OXIDATION NUMBER = the theoretical charge an atom would have in a molecule if every molecule was IONIC. This is as if the electrons were completely transferred. OXIDATION NUMBER = the theoretical charge an atom would have in a molecule if every molecule was IONIC. This is as if the electrons were completely transferred.

For example, in the compound H 2 O: For example, in the compound H 2 O: O has an electronegativity of 3.16 O has an electronegativity of 3.16 H has an electronegativity of 2.1 H has an electronegativity of 2.1 Since O is more electronegative than H, then we assume that the O removes the electron from each H and the oxidation numbers are: H = +1 O = -2 Since O is more electronegative than H, then we assume that the O removes the electron from each H and the oxidation numbers are: H = +1 O = -2

Redox reactions can be defined in terms of oxidation number: Redox reactions can be defined in terms of oxidation number: An element is said to be oxidized if its oxidation number increases in a reaction. An element is said to be oxidized if its oxidation number increases in a reaction. An element is said to be reduced if its oxidation number decreases in a reaction. An element is said to be reduced if its oxidation number decreases in a reaction.

Rules for Assigning Oxidation #’s Rule #1. The oxidation number of an atom of any element in its elemental state (uncombined form) is ZERO, no matter how complex the molecule. Rule #1. The oxidation number of an atom of any element in its elemental state (uncombined form) is ZERO, no matter how complex the molecule. H 2 = 0, F 2 = 0. Be = 0. Li = 0, Na = 0, O 2 = 0, P 4 = 0, S 8 = 0 H 2 = 0, F 2 = 0. Be = 0. Li = 0, Na = 0, O 2 = 0, P 4 = 0, S 8 = 0

RULE #2. For an ion composed of only one atom, the oxidation number is equal to the charge on the ion. RULE #2. For an ion composed of only one atom, the oxidation number is equal to the charge on the ion. K + = +1, Mg 2+ = +2, Al 3+ = +3, F - = -1, O 2- = -2 K + = +1, Mg 2+ = +2, Al 3+ = +3, F - = -1, O 2- = -2 All alkali metal ions (Li +, Na +, K +, Rb +, Cs +, Fr + ) have an oxidation number of +1. All alkali metal ions (Li +, Na +, K +, Rb +, Cs +, Fr + ) have an oxidation number of +1. All alkaline earth metal ions (Be +2, Mg +2, Ca +2, Sr +2, Ba +2, Ra +2 ) have an oxidation number of +2. All alkaline earth metal ions (Be +2, Mg +2, Ca +2, Sr +2, Ba +2, Ra +2 ) have an oxidation number of +2.

Rule #3: The oxidation number of oxygen in most compounds is –2 (e.g. H 2 O, CaO) Rule #3: The oxidation number of oxygen in most compounds is –2 (e.g. H 2 O, CaO) There are three exceptions to this rule: There are three exceptions to this rule: In OF 2 O=+2 since F is more electronegative than oxygen In OF 2 O=+2 since F is more electronegative than oxygen In H 2 O 2, or HO 2 -, or O 2 2- (the peroxide family) O= -1 In H 2 O 2, or HO 2 -, or O 2 2- (the peroxide family) O= -1 O 2 : the oxidation number is 0 (see rule #1) O 2 : the oxidation number is 0 (see rule #1)

Rule # 4. Fluorine has an oxidation number of –1 in all of its compounds. Rule # 4. Fluorine has an oxidation number of –1 in all of its compounds. Rule #5. The oxidation number of hydrogen is mostly +1, except when it is bonded to elements less electronegative than itself or if it is in its elemental form. Rule #5. The oxidation number of hydrogen is mostly +1, except when it is bonded to elements less electronegative than itself or if it is in its elemental form. NaHNa = +1, H = -1 NaHNa = +1, H = -1 CH 4 C = -4, H = +1 CH 4 C = -4, H = +1 H 2 H = 0 H 2 H = 0

Rule #6. In a NEUTRAL molecule, the sum of the oxidation numbers of all the atoms must be ZERO. In a POLYATOMIC ION, the sum of the oxidation numbers of all the atoms in the ion must be equal to the NET CHARGE of the ion. Rule #6. In a NEUTRAL molecule, the sum of the oxidation numbers of all the atoms must be ZERO. In a POLYATOMIC ION, the sum of the oxidation numbers of all the atoms in the ion must be equal to the NET CHARGE of the ion.

Examples Assign Oxidation Numbers to each element in the following: Assign Oxidation Numbers to each element in the following: a) NH 4 + a) NH 4 + b) Rb 2 O b) Rb 2 O c) H 2 Cr 2 O 7 c) H 2 Cr 2 O 7

Homework Optional: Read HEBDEN WORKBOOK Section 5-1 "Introduction". Do Exercises p.192 #1-2. Optional: Read HEBDEN WORKBOOK Section 5-1 "Introduction". Do Exercises p.192 # Optional: Read HEBDEN WORKBOOK Section 5-2 "Oxidation Numbers". Do Exercise p.194 # Optional: Read HEBDEN WORKBOOK Section 5-2 "Oxidation Numbers". Do Exercise p.194 # Do HANDOUT "Section 211/212 Provincial Exam Questions". 4. Do HANDOUT "Section 211/212 Provincial Exam Questions".