Chemistry 161.08 Fall 2013 Dr. Azizeh Farajallah Office: IB 2324C Phone number: 934-3940 Email:firstname.lastname@example.org Office hours: W/Th 5:00-5:50pm Lecture: M& W at 6:00-9:50pm Chapter 6-10
Grading? Exams: Tow exams (100pts each), cumulative final exam (150pts) Lab: 9 & 25pts each (lowest dropped). No make up lab and if missed more than one lab you receive 0.0 for the course Lab continue: I will discuss safety and lab policies in more details later! Worksheets: 8 & 20 pts each (lowest dropped). No make up. Instructor Evaluation/Notebook: (60 pts) your conduct in lecture (being on time) and lab (safety, notebook & cleaning)
Grading? • Extra Credit: Extra credit questions on exams • Attendance: for lecture, during the first week and for lab, attendance is taken for every lab. Missed lectures or lab? • Responsibility: You are responsible for everything covered in lecture and assigned from the book. • Waiting List: Depending on first week attendance and drop out rate?
Grading? Rough Grading Scale: 100 – 94 % 4.0 90 % 3.7 70% 2.0 85 % 3.5 65 % 1.5 80% 3.0 60 % 1.0 75% 2.5 55 % 0.7 <55% 0.0
Night class challenges! • Please come a wake and try to stay a wake • 4 hours night class will be a challenge no matter what!
Chemistry 161.08 Fall 2013 Mondays: Lecture 6:00-8:50 pm with breaks Worksheet: 8:50-9:50pm Wednesday: Lecture 6:00-8:00 pm with a break Lab: 8:00-9:50pm Dr. Tracy Furutani
How to succeed in this course? • Attend lectures (seek help if you miss a lecture) • Practice end of chapters HW • Don’t miss any of the worksheets or labs • Submit reports and prelabs on time • Form a study group
What is chemistry? Chemistry is the study of matter
Chemistry around us! p. 4
Matter? • Matter is every thing around you, it is anything that has mass and occupies space.
Elements and atoms? • All matter is made of atoms • Atoms are the building blocks of matter, sort of how bricks are the building blocks of houses. • Elements are the alphabet of chemistry. • Elements are made of atoms.
Atomic structure review • Which subatomic particles are represented by the pink spheres? • Answer: electrons • Which subatomic particles are represented by the yellow and blue spheres? • Answer: protons and neutrons • What structure do the yellow and blue spheres form? • Answer: the nucleus
Oxidation-reduction reactions Chapter 6
What are oxidation & reduction? A history lesson: • Oxidation “originally” was defined as a process (reaction) in which a substance gains oxygen (oxide). CH4 + 2O2 -> CO2 + 2H2O
What are Oxidation & Reduction? A history lesson cont: • No oxidation can occur without another substance losing oxygen; the substance losing oxygen is reduced(reduction). • Reactions that involve the transfer of oxygen were known as oxidation-reduction reactions (or redox reactions). • Oxidation and reduction occur simultaneously
Electron Shift in Redox Reactions • The “MODERN” concept of oxidation-reduction • Redox reactions are currently defined as a reaction that involves the transfer of electrons between reactants. • Oxidation – is the complete or partial loss of electrons or gain of oxygen. • Reduction – is the complete or partial gain of electrons or loss of oxygen.
Involves 2 processes: Oxidation = Loss of electrons Na Na+ + e–Oxidation Half-Reaction Reduction= Gain of electrons Cl2 + 2e– 2Cl–Reduction Half-Reaction Net reaction: 2Na + Cl2 2Na+ + 2Cl– Oxidation and reduction always occur together Can't have one without the other Oxidation–Reduction Reactions
Oxidation-reduction reactions Electron transfer reactions • Electrons transferred from one substance to another Lose e - =Oxidation • Cu (s) + 2 Ag+ (aq) Cu2+ (aq) + 2 Ag(s) Gain e - =Reduction
Oxidation of zinc: reduction of copper zinc is being oxidized while copper is being reduced. Why?
Guidelines for redox reactions • Oxidation and reduction always occur simultaneously • Total number of electrons lost by one substance equals total number of electronsgained by second substance • 2Na + Cl2 2Na+ + 2Cl– • For a redox reaction to occur, something must accept electrons that are lost by another substance
Oxidation numbers • Oxidation numbers (O.N.) are positive or negative numbers assigned to elements in chemical formulas according to a set of rules. • Bookkeeping Method: a way to keep track of electrons • Rule 1: The O.N. must add up to the charge on the molecule, formula unit or ion. For example: • MgSO4: O.N. of [Mg] + [4O]+ [S]= 0 • Mg2+ O.N=+2, O2- O.N= -2, and Cl- = -1. • Rule 2: The O.N. of free elements (any uncombined element) is 0. For example: • Fe O.N= 0, Cl2 O.N= 0, and Ca O.N= 0
Oxidation numbers • Rule 3: Metals in groups 1A, 2A, 3A if they are in compounds have O.N. +1, +2 and +3 respectively. For example: Na2S (Na = +1) and Ca(NO3)2 (Ca = +2) • Rule 4:The O.N. of H and F is +1, -1 respectively. For example: HBr (H = +1) and HF(H = +1, F=-1) • Rule 5:The O.N. of oxygen is -2. For example: MgO (O = -2), HBrO3 (O = -2)
Oxidation numbers • Rule 6, 7 and 8: The O.N.of Group 7A, 6A and 5A is -1, -2 and -3 respectively • Rule 9: When there is a conflict between the rules or an ambiguity in assigning an oxidation number, apply the rule with the lower number and ignore the conflicting rule. Example: if there is a conflict between rule 1 and 6, then rule 1 takes precedents over rule 6.
Redefine oxidation-reduction in terms of oxidation number Oxidation: • Increase in oxidation number • Electron loss • Gain oxygen Reduction: • Decrease in oxidation number • Electron gain • Loss of oxygen
Oxidation/reduction: remembering which is which! “LEO the lion goes GER.” Losing Electrons is Oxidation Gaining Electrons is Reduction
Assigning oxidation number • Li2O Li (2 atoms) × (+1) = +2 (Rule 3) O (1 atom) × (–2) = –2 (Rule 5) sum = 0 (Rule 1) +2 –2 = 0 so the charges are balanced to zero • CO2 C (1 atom) × (x) = x O (2 atoms) × (–2) = –4 (Rule 5) sum = 0 (Rule 1) x –4 = 0 or x= +4 C is in +4 oxidation state
Learning check Assign oxidation numbers to all atoms: Ex. 1ClO4– O (4 atoms) × (–2) = –8 Cl (1 atom) × (–1) = –1 (molecular ion) sum ≠ –1 (violates Rule 1) Rule 5 for oxygen comes before Rule 6 for halogens O (4 atoms) × (–2) = –8 Cl (1 atom) × (x) = x sum = –1 (Rule 1) –8 + x = –1 or x = 8 – 1 So x = +7; Cl is oxidation state +7
Learning check Assign oxidation states to all atoms: • MgCr2O7 Mg =+2; O = –2; and Cr = x (unknown) [+2] + [2x] + [7 × (–2)] = 0 2x – 12 = 0 x = +6 Cr is oxidation number of +6 • KMnO4 K =+1; O = – 2; so Mn = x [+1] + [x] + [4 × (–2)] = 0 x – 7 = 0 x = +7 Mn is oxidation number of +7
Practice exercises • 6.1: When sodium reacts with molecular oxygen, O2, the product is sodium peroxide, Na2O2, which contains the peroxide ion, O22−. In this reaction, is O2 oxidized or reduced? (Hint: Which reactant gains electrons, and which loses electrons?) • Na + O2 Na2O2 0 0 +1 -1 • Oxygen is reduced since it gains electrons. Sodium is oxidized since it loses electrons.
Review problems • 6.23 Assigne Oxidation numbers to the atoms in the following: • A. S 2- • O.N.= -2 • B. SO2 • S= -2, O= -2, SO2 = 0 • [-2] + [2x-2] = 0 violate rule 1 • Rule of oxygen proceed that for S • [S] + [-4] = 0 and therefore O.N of S is +4 • C. P4 • O.N. of P is 0
Review problem 6.25 • Assigne oxidation number to each of the following atom in the following: • A. NaOCl • [+1] + [-2] + [-1] = 0 violates rule 1 • The rules for oxygen and sodium proceeds that for Clso • [+1] + [-2] + [Cl] = 0 and therefore O.N. for Cl is +1 • B. NaClO2 • [+1] + [-1] + [2x-2] = 0 violates rule 1 • The rules for oxygen and sodium proceeds that for Cl so • [+1] + [Cl] + [-4] = 0 and therefore O.N. for Cl is +3
Review problem 6.25 cont, • C. NaClO3 • [+1] + [-1] + [3x-2] = 0 violates rule 1 • The rules for oxygen and sodium proceeds that for Cl so • [+1] + [Cl] + [-6] = 0 and therefore O.N. for Cl is +5 • C. NaClO4 • [+1] + [-1] + [4x-2] = 0 violates rule 1 • The rules for oxygen and sodium proceeds that for Cl so • [+1] + [Cl] + [-8] = 0 and therefore O.N. for Cl is +7
Oxidizing and reducing agents Oxidizing Agent • Substance that accepts electrons • Accepts electrons from another substance • Substance that is reduced • Cl2 + 2e– 2Cl– ReducingAgent • Substance that donates electrons • Releases electrons to another substance • Substance that is oxidized • Na Na+ + e–
Example • Assign oxidation numbers to each of the following elements of the following equations and identify the oxidizing and reducing agents? • A. H2 (g) + Cl2 (g) → 2 HCl (g) • The oxidizing agent is Cl2. • The reducing agent is H2. • H2O (g) + CH4 (g) → CO (g) + 3 H2 (g) • The oxidizing agent is H2O. • The reducing agent is CH4.
Example continue • c. CuO (s) + H2 (g) → Cu (s) + H2O The oxidizing agent is CuO. The reducing agent is H2. • B2O3 (s) + 3 Mg (s) → 2 B (s) + 3 MgO (s) The oxidizing agent is B2O3. The reducing agent is Mg.
Practice exercises • 6.2 Identify the substances oxidized and reduced, and the oxidizing and reducing agents in the reaction of aluminum and chlorine to form aluminum chloride. • Al + Cl2 AlCl3 0 0 +3 -1 Aluminum loses electron = oxidized and therefore is the reducing agent. Chlorine gain electrons = reduced and therefore is the oxidizing agent.
Review problem 6.35 • For the following reactions, identify the substance oxidized, the substance reduced, the oxidizing agent and the reducing agent. • A. 2HNO3 + 3H3AsO3 2NO+ 3H3AsO4 + H2O • +5 +3 +2 +5 • N gained electrons, HNO3 reduced and therefore is an oxidizing agent. • As lost electron, H3AsO3 is oxidized and therefore is a reducing agent. • B. NaI + 3HOCl NaIO3 + 3HCl • -1 +1 +5 -1 • NaI lost electrons, NaI is oxidized and therefore a reducing agent • Cl gained electrons, HOCl is reduced and therefore it is an oxidizing agent
Redox reactions examples • Very common • Batteries—car, flashlight, cell phone, computer • Metabolism of food • Combustion • Chlorine Bleach • Dilute NaOCl solution • Cleans through redox reaction • Oxidizing agent • Destroys stains by oxidizing them
Redox reactions e.g. Fireworks displays Net:2Mg + O2 2MgO Oxidation: Mg Mg2+ + 2e– • Loses electrons = oxidized • Reducing agent Reduction: O2 + 4e– 2O2– • Gains electrons = reduced • Oxidizing agent
Oxidation reduction: redox chemistry Oxidation occurs when a molecule does any of the following: • Loses electrons • Gains oxygen • Increase in oxidation number If a molecule undergoes oxidation, it is the reducing agent.
Oxidation reduction: redox chemistry Reduction occurs when a molecule does any of the following: Gains electrons Loses oxygen Decrease in oxidation number If a molecule undergoes reduction, it is the oxidizing agent.