IB topic 9 Oxidation-reduction

Define oxidation and reduction in terms of electron loss and gain.

Taking notes Do not copy, write in your own

words or draw diagrams or pictures 10 % better performance if you

copy 35% better performance if you write

in your own words

2Mg + O2 2MgO

Reduction-charge goes down OILRIG Redox always occurs together Question 1

A:  

B

C

D

9.2Redox equations

Deduce simple oxidation and reduction half-equations given the species involved in a redox reaction.

2Fe + 3Cl2 2FeCl3

Deduce the oxidation number of an element in a compound.

+ means loss, – gain of e-

Rules Elements Na, O2, S8 = 0 Group 1 = +1 H=+1 O = -2 halides -1 Many exceptions Ox. # add up to the charge on the species In covalent compounds more

electronegative is – ie NH3, CCl4

Give Ox. numbers to each element H2SO4, SO3

2-

NH4+, Fe2O3, K2Cr2O7, CuCl2,

Question 2 Question 3

State the names of compounds using oxidation numbers.

MnO2, FeO, CuCl, Na2O Manganese (IV) oxide, iron (II)

oxide, Copper (I) chloride, sodium oxide

[Cu(H2O)6]2+ [CuCl4]2-

Hexaaquacopper(II) ion Tetrachlorocopper (II) ion

Deduce whether an element undergoes oxidation or reduction in reactions using oxidation numbers.

Ca + Sn2+ Ca2+ + Sn

4NH3 + 5O2 4NO + 6H2O

Disproportionation Cl2 + H2OHCl + HClO

Question 4

Deduce redox equations using half-equations.

Steps Assign O numbers and write half reactions Balance atoms other than H and O Balance O by adding H2O as needed Balance H by adding H+ as needed Balance Charges by adding e- to the +

side Equalize the e- by multiplying Add the half reactions together

Try NO3- + Cu NO + Cu2+

+5, -2, 0 on left +2,-2,+2 on right Cu Cu2+ ox NO3

- NO red 4H+ + NO3

- NO + 2 H2O Cu Cu2+ + 2e- 4H+ + NO3

- + 3e- NO + 2 H2O 8H+ + 2NO3

- + 6e- + 3Cu 2NO + 4H2O + 3Cu2+ + 6e-

Fe+2 + MnO4- Fe+3 + Mn+2

SO32- + Cr2O7

2- SO42- + Cr3+

Internet example Question 5

Define the terms oxidizing agent and reducing agent.

A substance that gets reduced causes oxidation so it is an oxidizing agent

Identify the oxidizing and reducing agents in redox equations.

Fe2O3 + 3C 2Fe + 3CO2

Fe oxidizing C reducing IO3

- + 5I- + 6H+ 3I2 +3H2O

IO3- oxidizing I- reducing

question 6

9.3Reactivity

Deduce a reactivity series based on the chemical behavior of a group of oxidizing and reducing agents.

More reactive metals lose their e- more readily becoming a strong reducing agent

Zn + CuSO4

Stronger Mg, AL, Zn, Fe, Pb, Cu, Ag simulation

Non metals F2 strongest oxidizing agent, most readily becomes reduced Cl2, Br2, I2

Question 7

Deduce the feasibility of a redox reaction from a given reactivity series.

Yes or no ZnCl2 + Ag

2FeCl3 + 3 Mg

Cl2 + 2KI question 8

9:4 Voltaic Cells (battery)9:4 Voltaic Cells (battery)

Explain how a redox reaction is used to Explain how a redox reaction is used to produce electricity in a voltaic cellproduce electricity in a voltaic cell

Zn(s) Zn(s) → Zn→ Zn2+2+(aq) + 2e(aq) + 2e-- red. Agent red. Agent

Other half cellOther half cell

CuCu2+2+ + 2e + 2e-- → Cu(s) reduced → Cu(s) reduced

This combination is a voltaic cellThis combination is a voltaic cell

State that oxidation occurs at the State that oxidation occurs at the negative electrode (anode) and negative electrode (anode) and reduction occurs at the positive reduction occurs at the positive

electrode (cathode)electrode (cathode)Which is the anode (where eWhich is the anode (where e-- leave) leave) /cathode?/cathode?

Draw this setup.Draw this setup.

Animation Animation

Draw Zn/ZnDraw Zn/Zn2+2+ and Ag/Ag and Ag/Ag++ and give the and give the potential, show the flow of epotential, show the flow of e--

Where is oxidation and reductionWhere is oxidation and reduction

Connect these half cells with a salt bridgeConnect these half cells with a salt bridge

this is a spontaneous reactionthis is a spontaneous reaction

AnimationAnimation

Question 9Question 9

9:5 Electrolytic cells9:5 Electrolytic cells

Describe, using a diagram, the essential Describe, using a diagram, the essential components of an electrolytic cell.components of an electrolytic cell.

Opposite of a voltaic cellOpposite of a voltaic cell

Requires electrical energyRequires electrical energy

│ │ means + then – in diagramsmeans + then – in diagrams

AnimationAnimation

The power source pushes e- to the – The power source pushes e- to the – electrodeelectrode

-electrode attracts + ions-electrode attracts + ions

-electrode is the cathode cations gain e- -electrode is the cathode cations gain e- so are reducedso are reduced

Show the electrolysis of MgFShow the electrolysis of MgF22

Describe how current is conducted Describe how current is conducted in an electrolytic cellin an electrolytic cell

Do questions 10Do questions 10

Deduce the products of the Deduce the products of the electrolysis of a molten saltelectrolysis of a molten salt

Diagram the electrolysis of molten(melted) Diagram the electrolysis of molten(melted) NaClNaCl

Tell where oxidation and reduction occursTell where oxidation and reduction occurs

Do question 11Do question 11

19.1 Standard electrode 19.1 Standard electrode potentialspotentials

Describe the standard hydrogen electrode.Describe the standard hydrogen electrode.

Standard H cellStandard H cell

Conditions - Pt electrodeConditions - Pt electrode

HH22 gas at 1 atm pressure gas at 1 atm pressure

1 mol dm1 mol dm-3-3 H H++

298 K or 25298 K or 25ooCC

0.00 V0.00 V

Attach a half cell if e- flows to HAttach a half cell if e- flows to H22 it is – it is –

Like Zn which is -0.76 VLike Zn which is -0.76 V

conventionsconventions

Zn(s)/ZnZn(s)/Zn+2+2││H││H++(aq)/1/2 H(aq)/1/2 H22(g) (Pt)(g) (Pt)

Oxidation on left sideOxidation on left side

More – value of electrode potentials give More – value of electrode potentials give off e-off e-

Define the term Define the term standard electrodestandard electrodepotential potential ((E E Ö ) .Ö ) .

relative electrode potential compared under relative electrode potential compared under standard conditions with the standard standard conditions with the standard hydrogen electrodehydrogen electrode

Look at your data bookletLook at your data booklet

19.1.3 Calculate cell potentials 19.1.3 Calculate cell potentials usingusing

standard electrode potentials.standard electrode potentials.Try CrTry Cr22OO77

2- 2- and Br and Br22

Answer 0.26 VAnswer 0.26 V

Predict whether a reaction willPredict whether a reaction willbe spontaneous using standardbe spontaneous using standard

electrode potential values.electrode potential values.

Can a solution of tin II ions reduce a Can a solution of tin II ions reduce a solution of iron III ions?solution of iron III ions?

Yes 0.91VYes 0.91V

Can a solution of SnCan a solution of Sn4+4+ ions reduce Fe ions reduce Fe3+ 3+ to to FeFe

SnSn4+4+ + 2 e- + 2 e- → Sn→ Sn2+2+ E Eoo = +1.33 = +1.33No what does work No what does work

Do question 12Do question 12

19.2 Electrolysis19.2 Electrolysis

Predict and explain the products of Predict and explain the products of electrolysis of aqueous solutions.electrolysis of aqueous solutions.

For water need DC in a dilute solution of For water need DC in a dilute solution of HH22SOSO44

HH++ to H to H22 given off at the – electrode given off at the – electrode

OHOH-- to O to O22 at the + electrode at the + electrode

2H2H22O O 4H 4H++ + O + O22 + 4 e- + 4 e-

Electrolysis of NaClElectrolysis of NaCl(aq)(aq)

- electrode H- electrode H22

+ electrode dilute OH+ electrode dilute OH- - to Oto O22 conc Cl conc Cl-- to Cl to Cl22

Write half reactions Write half reactions

Do question 13Do question 13

Determine the relative amounts of Determine the relative amounts of thethe

products formed during electrolysis.products formed during electrolysis.

Position in the electrochemical seriesPosition in the electrochemical series

+ ions lower in the series will gain e- at the + ions lower in the series will gain e- at the – electrode (cathode) in preference to – electrode (cathode) in preference to those higherthose higher

Hydroxide ions release e- to form oxygen Hydroxide ions release e- to form oxygen and Hand H22O in preference to other anions at O in preference to other anions at

the positive electrodethe positive electrode

In some cases concentrations ( more In some cases concentrations ( more concentrated may be discharged)concentrated may be discharged)

Nature of the electrode C and Pt are inertNature of the electrode C and Pt are inert

List all the cations and anionsList all the cations and anions

Cations lower in the series gain e- more Cations lower in the series gain e- more readilyreadily

Describe the use of electrolysis inDescribe the use of electrolysis inelectroplating.electroplating.

CuSOCuSO4(aq)4(aq) with copper electrodes with copper electrodes

CuCu2+2+ goes to – electrode and plates Cu goes to – electrode and plates Cu

+ electrode Cu goes to Cu+ electrode Cu goes to Cu2+2+(use impure (use impure ore)ore)

ElectroplatingElectroplating

Object to be electroplated is put at the Object to be electroplated is put at the negatinegative ve electrode and is placed in a electrode and is placed in a solution of ions of the metal used to plate solution of ions of the metal used to plate it.it.

Factors affecting relative amountsFactors affecting relative amounts

Charge on the ionsCharge on the ions

NaNa+ + CuCu2+2+ Al Al3+3+ Al takes more energy to Al takes more energy to makemake

Quantity of e- (amperage and time) charge Quantity of e- (amperage and time) charge = current x time= current x time

Do question 14Do question 14

Do questions 1-14 on chapter 10 in your Do questions 1-14 on chapter 10 in your IB Study Guide and turn inIB Study Guide and turn in