May 27 - Chapter 17 textbookMay 27 - Chapter 17 textbookTopic 9 review bookTopic 9 review book

OXIDATION-REDUCTION OXIDATION-REDUCTION

• Objective :To determine O.N. for atoms in Objective :To determine O.N. for atoms in elements and compounds.elements and compounds.

• To recognize redox reactionsTo recognize redox reactions

• HW : Complete worksheet. STUDY HW : Complete worksheet. STUDY PAGE 606-607 from textbookPAGE 606-607 from textbook

DO NOWOBSERVATION SKILLS!

• In your notebook record the experiment in words and then describe the experiment like a chemist (with a CHEMICAL REACTION! )

• Indicate the metal and the non metal• How metals react?• How non metals react?• Review : draw the dot diagram for each

element, and for the compound formed• How many electrons and protons in each

reactant?• How many electrons and protons in each

element in the product?

REDOX REACTIONS (electron REDOX REACTIONS (electron transfer reactions)transfer reactions)

• Whenever an atom loses an electron Whenever an atom loses an electron another atom has to gain one. Both another atom has to gain one. Both reactions are simultaneous.reactions are simultaneous.

Mg + OMg + O2 2 MgO MgO

Magnesium lost 2 electrons because oxygen Magnesium lost 2 electrons because oxygen took them. The metal LOST electrons, the took them. The metal LOST electrons, the NON METAL GAINED electronsNON METAL GAINED electrons

What happens to a car when the paint chips off?

LEOLEO GERGER

LLosingosing EElectrons islectrons is OOxidation.xidation.

GGainingainingEElectrons islectrons isRReductioneduction

OIL RIGOIL RIG

• OOxidationxidation• IIss• LLoss.oss.

• RReduction eduction • IIss GGain.ain.

REDOX REACTIONS

• REDuction – OXidation reactions

• Electrons are transferred from the element that is being oxidized to the one that is being reduced.

Oxidation Number (O.N.)Oxidation Number (O.N.)

• Chemist use the O.N. to determine how Chemist use the O.N. to determine how many electrons are either gained or lost by many electrons are either gained or lost by an atom or ion in a chemical reaction.an atom or ion in a chemical reaction.

• O.N. is the charge or partial charge of an O.N. is the charge or partial charge of an atom in a compound or an ion.atom in a compound or an ion.

RULES FOR ASSIGNING O.N.RULES FOR ASSIGNING O.N.

1. For all uncombined elements O.N. = O 1. For all uncombined elements O.N. = O (FREE ELEMENTS)(FREE ELEMENTS)

2. For monoatomic ions the charge equals O.N.2. For monoatomic ions the charge equals O.N.

3. Metals of group 1 in compounds O.N.= +1.3. Metals of group 1 in compounds O.N.= +1.

Metals of group 2 in compounds O.N.= +2Metals of group 2 in compounds O.N.= +2

4. Fluorine in compounds is always – 1.4. Fluorine in compounds is always – 1.

Other halogens -1 in binary compounds Other halogens -1 in binary compounds with metals.with metals.

5. Hydrogen + 1 except in metal hydrides 5. Hydrogen + 1 except in metal hydrides (combined with metals of group 1 or 2)(combined with metals of group 1 or 2)

6. Oxygen is -2 except when combined with 6. Oxygen is -2 except when combined with F (is =2) or in peroxides (-1).F (is =2) or in peroxides (-1).

• 7. THE SUM OF THE OXIDATION 7. THE SUM OF THE OXIDATION NUMBERS IN ALL COMPOUNDS MUST NUMBERS IN ALL COMPOUNDS MUST BE ZERO BE ZERO

• 8. FOR POLYATOMIC IONS THE SUM 8. FOR POLYATOMIC IONS THE SUM OF THE O.N. IS EQUAL TO THE OF THE O.N. IS EQUAL TO THE CHARGE OF THE IONCHARGE OF THE ION

Group work

• Get in your groups and practice what you just have learnt and complete handout.

• Finish the rest for homework.

Answer to finding the Oxidation state

1. +7

2. +5

3. +5

4. +7

5. +4

6. +6

7. +2

8. +3

9. +5

10.+3

11.+6

ReviewFind the O.N. for each element

• Cl2• K2S2O3

• NO3-

• PO43-

• CaCr2O7

• KNO2

• OF2

• H2O2

• KH

May 28May 28

• Objective: How to keep track of electron Objective: How to keep track of electron transfers in chemical reactions?transfers in chemical reactions?

• HW: finish worksheetHW: finish worksheet

• Answer question 11 to 31 in page 162 RBAnswer question 11 to 31 in page 162 RB

VOCABULARY

• SIMULTANEOUS = at the same time

• OXIDATION = to lose electrons

• REDUCTION = to gain electrons

• OXIDATION NUMBER = charge or partial charge over an element.

DO NOWOBSERVATION SKILLS!

• In your notebook record the experiment in words and then describe the experiment like a chemist (with a CHEMICAL REACTION! )

PRACTICE

• HCl + Mg -> MgCl2 + H2

• Indicate the oxidation state of each element in the reaction.

To recognize redox reactions…To recognize redox reactions…

• Look for changes in the oxidation number Look for changes in the oxidation number or the atoms. If one element changed the or the atoms. If one element changed the O.N. then for SURE is a redox reaction.O.N. then for SURE is a redox reaction.

• All single replacement, synthesis, All single replacement, synthesis, decomposition and combustion reactions decomposition and combustion reactions are REDOX.are REDOX.

• Double replacement reactions are not Double replacement reactions are not redox.redox.

PRACTICE – your turn!

• Get in pairs and work with the reactions in the handout (section # 7). Determine the O.N. for each element and decide which element got oxidized and which got reduced (TIP : LOOK ALWAYS IN THE REACTANTS SIDE!!!)

AGENTS

• They are always the REACTANTS!!!

REDUCING AGENT

• When a substance is oxidized it LOSES electrons.

Its O.N. increases. It is being oxidized and Its O.N. increases. It is being oxidized and is making the other substance in the is making the other substance in the reaction reduced. Then the one that gets reaction reduced. Then the one that gets oxidized is the REDUCING AGENT.oxidized is the REDUCING AGENT.

R.A. gets oxidized. R.A. gets oxidized.

Its O.N. increasesIts O.N. increases

Active metals are good RAActive metals are good RA

OXIDIZING AGENTS

• When a reactant is reduced it GAINS electrons. Its O.N. decreasesIts O.N. decreases. By being . By being reduced, it takes electrons from the other reduced, it takes electrons from the other specie, it makes the other specie to get specie, it makes the other specie to get oxidized. oxidized.

• The reactant that gets reduced is the The reactant that gets reduced is the OXIDIZING AGENT.OXIDIZING AGENT.

• Oxidizing Agent : Reactant that gets reduced - Oxidizing Agent : Reactant that gets reduced - Its ON decreases.Its ON decreases.

Reducing Agents

• Is the reactant that gets oxidized and makes the other reactant get reduced.

• Since it gets oxidized its ON increases.

• 2Mg + O2Mg + O2 2 MgO MgO

• Mg: oxidation number changes from

• 0 to +2 . It increased.

• Mg gets oxidized. Is the reducing agent.

• Oxygen: Oxidation number changes from 0 to -2 , it decreases is the Oxidizing agent.

P 162 answers( identifying Agents)11)2

12)1

13)2

14)2

15)1

16)3

17)3

18)4

19)1

20)2

21)4

• 22)2 32)1• 23)3• 24)1• 25)2• 26)1• 27)3• 28)2• 29)1• 30)3• 31)2

May 29

• How to recognize oxidizing and reducing agents? More practice

• How to separate a redox reaction into half reactions?

• Hw p 164 q 32 to 36

• Do Now

• Find the ON of P in Calcium Phosphate

ANSWERS TO REDOX WORKSHEET 1

• 1a) zero• b) the charge of the ion• c) zero• d) the charge of the ion• 2 a) +4 b) 0 c) +3 d) +5 e) +3 f)+5• 3 a)S +3 O -2 b) Cl 0 • c) C +4 O -2 d)N +6 O -2 • e) K +1 Cl -1 f)He 0 g) N +4 O -2 • h ) H +1 N -3

Half reactionsHalf reactions

• A redox reaction can always be broken A redox reaction can always be broken down as 2 half reactions that show the down as 2 half reactions that show the atom or ion that is being oxidized and the atom or ion that is being oxidized and the one that is being reduced.one that is being reduced.

• MASS AND CHARGE has to be MASS AND CHARGE has to be conserved in a half reactionconserved in a half reaction

• 1. find the o.n. of each element in the 1. find the o.n. of each element in the reaction. Determine which is being reaction. Determine which is being reduced an which is being oxidizedreduced an which is being oxidized

• 2. Balance the masses first2. Balance the masses first

• 3. Complete each half reaction with 3. Complete each half reaction with electrons.( LEO GER)electrons.( LEO GER)

• 4. Verify that masses and charges are 4. Verify that masses and charges are balanced.balanced.

May 30May 30

• Objetive: Spontaneous Redox ReactionObjetive: Spontaneous Redox Reaction

• To use table J to predict if a single To use table J to predict if a single replacement reaction will occurr.replacement reaction will occurr.

Answers RB Page 164Half reactions

32)1

33)3

34)3

35)2

36)4

Take home testRedox Chapter

• Do Practice Questions for New York Regents Exam. Page 169 Review Book

• Questions 1to 30 MC in scantron. Begin using scantron at Q 51.

• Answer questions 31, 32 and 34 in the green box in the scantron sheet.

• You MUST hand in the scantron sheet as you walk into the classroom Monday June 3!!!

Activity seriesActivity series• Spontaneous Reactions : happen Spontaneous Reactions : happen

without external helpwithout external help..

CuSOCuSO4 4 + Zn + Zn Zn SO Zn SO4 4 + Cu+ Cu

• In a single replacement reaction the In a single replacement reaction the most active element replaces the other most active element replaces the other element from a compound. (TABLE J)element from a compound. (TABLE J)

Table JTable J

• The metal above gets oxidized the one The metal above gets oxidized the one below will get reduced.below will get reduced.

• For non metals the one above gets For non metals the one above gets reduced the one below gets oxidized.reduced the one below gets oxidized.

• FF2 2 + NaCl+ NaCl

• II2 2 + NaCl + NaCl

• ClCl22 + Na I + Na I

METALS IN TABLE JMETALS IN TABLE J

• The higher the metal is in table J, the most The higher the metal is in table J, the most active it is, the more tendency to became active it is, the more tendency to became oxidized (lose electrons)oxidized (lose electrons)

• On Top of table J best reducing agentsOn Top of table J best reducing agents

• Towards the bottom metals tend to gain Towards the bottom metals tend to gain electrons then they became reduced and electrons then they became reduced and are good reducing agents are good reducing agents

Non MetalsNon Metals

• FF2 2 has the greatest tendency to gain has the greatest tendency to gain

electrons ( became reduced) is the BEST electrons ( became reduced) is the BEST OXIDIZING AGENT.OXIDIZING AGENT.

Predict if the reaction will occurPredict if the reaction will occur

• Ag (NOAg (NO33) + Cu ) + Cu

• ZnZn+2 +2 + Co + Co

• MgClMgCl2 2 + Ni + Ni

• K + FeClK + FeCl33

• Li + Mg Li + Mg 2+2+

ELECTROCHEMISTRY• OBJECTIVE: To distinguish between

electrochemical and electrolytic cells

• To identify the different parts of a cell and explain their purpose.

Do nowDo now

• What SPONTANEOUS reaction would occur if What SPONTANEOUS reaction would occur if we have we have

• Cu, CuCu, Cu2+2+, Zn and Zn, Zn and Zn2+ 2+ together. together.

• Hint USE TABLE JHint USE TABLE J

• Where the electrons flow? Which loses which Where the electrons flow? Which loses which gains?gains?

Electrochemistry

Voltaic Cells

In spontaneous oxidation-reduction (redox) reactions, electrons are transferred and energy is released.

IDEA!IDEA!

• If we can place the two metals in two If we can place the two metals in two different containers and connect them different containers and connect them with a wire the electrons will flow from the with a wire the electrons will flow from the Zn to the Cu and we will have an electric Zn to the Cu and we will have an electric current – ELECTRICITYcurrent – ELECTRICITY

• But it does not work if we do not close the But it does not work if we do not close the circuit – USE A SALT BRIDGEcircuit – USE A SALT BRIDGE

Voltaic Cells

• A typical cell looks like this.

• The oxidation occurs at the anode.

• The reduction occurs at the cathode.

ELECTRODES

• Where the reduction or oxidation takes place. They are usually metals or they can be made of graphite.

• RED CAT

• REDuction at the cathode

ELECTROCHEMISTRYELECTROCHEMISTRY

• *Anode: where the oxidation occurs.*Anode: where the oxidation occurs.

• *Cathode: where the reduction occurs.*Cathode: where the reduction occurs.

• Voltaic or galvanic cellVoltaic or galvanic cell: produce : produce ELECTRICITYELECTRICITY from an spontaneous from an spontaneous chemical reaction. chemical reaction.

• ELECTRON FLOW. FROM THE ONE ELECTRON FLOW. FROM THE ONE THAT GETS OXIDIZED TO THE ONE THAT GETS OXIDIZED TO THE ONE THAT GETS REDUCED.THAT GETS REDUCED.

• POLARITIES POLARITIES

• ANODE – NEGATIVE source of electronsANODE – NEGATIVE source of electrons

• CATHODE- POSITIVECATHODE- POSITIVE

A typical voltaic cell

Cathode: the electrode at which reduction occurs

Anode: the electrode at which oxidation occurs

RED CAT

REDuction at the cathode

Salt bridge: a tube containing strong electrolyte, a pathway to allow the ions to move from one side to another. PERMIT THE MIGRATION OF IONS

Problems

1. A cell uses the reaction Mn + Ni2+ Ni + Mn2+ to produce electricity.

a)Write the half-reaction that occurs at the anode.

b) Write the half-reaction that occurs at the cathode.

c) Which species in this cell loses electrons?

d) As the cell produces electricity, which ion increases in concentration?

Mn Mn2+ + 2e-

Ni2+ + 2e- Ni

Mn

Mn2+

1. Voltaic Cell

A type of electrochemical cell that converts chemical energy to electrical energy by a spontaneous redox reaction.

In 1800, Volta built the voltaic pile and discovered the first practical method of generating electricity. Constructed of alternating discs of zinc and copper, with pieces of cardboard soaked in salt water b/w the metals, the voltaic pile produced electrical current.

Electrochemical cellAn apparatus that uses a redox reaction to produce electrical energy

(voltaic cell) or uses electrical energy to cause a chemical reaction

(electrolytic cell).

Electrolytic cellElectrolytic cell

• Uses electricity toUses electricity to force force a reaction that is a reaction that is not spontaneous to occur.not spontaneous to occur.

• NOTICE THAT IN ELECTROLYTIC NOTICE THAT IN ELECTROLYTIC CELLS THERE IS A BATTERY OR A CELLS THERE IS A BATTERY OR A POWER SOURCE PRESENTPOWER SOURCE PRESENT

• ElectrolysisElectrolysis: to decompose a : to decompose a substance using electricity substance using electricity

ElectroplatingElectroplating

Is used to cover an object with metal using Is used to cover an object with metal using electricity.electricity.

• THE OBJECT TO BE COVERED GOES THE OBJECT TO BE COVERED GOES IN THE CATHODEIN THE CATHODE

• POLARITIES : ANODE – POSITIVEPOLARITIES : ANODE – POSITIVE

• CATHODE- NEGATIVE SOURCE OF CATHODE- NEGATIVE SOURCE OF ELECTRONS – CONNECTED TO ELECTRONS – CONNECTED TO NEGATIVENEGATIVE

P 160 rb 1) 1

2) 2

3) 4

4) 4

5) 3

6) 1

7) 4

8) 2

9) 1 10)2