redox presentation 11 july 2011

REDOX1.A.DEFINATION

Transfer of electrons Oxidation is

reduction is

PROCESS WHERE ELECTRON IS RELEASED

PROCESS WHERE ELECTRON IS GAINED

change in oxidation numberOxidation is

reduction is

PROCESS WHERE OXIDATION NUMBER INCREASE

PROCESS WHERE OXIDATION NUMBER DECREASE

b.Calculate the oxidation number of i.Chromium in K2Cr2O7

ii. Chlorine in ClO4-

iii.Oxygen in H3O+.

2(+1) + 2x +7(-2) =0. , Cr = +6

x +4(-2) =-1. , Cl= +7

3(+1) +x =+1. , O= -2

c.IUPAC nomenclature

i.K2CrO4

ii.MgSO4

Potasium Chromate (VI)

Magnesium sulphate(VI)

iii.HNO3

iv.HNO2

nitric acid (V)

Nitric acid (III)

d. Redox & non redox reaction. reasonsi. Zn + CuSO4 Cu + ZnSO4

ii. ZnCO3 ZnO + CO2

Redox reaction because the oxidation number of Zn Change from 0 to +2

Non Redox reaction because the oxidation number of Zn no change,( from +2 to +2)

B) Br2 + 2KI I2 + 2KBr i.name of this reaction

ii.change in oxidation number of bromine

iii. change in oxidation number of iodine

Displacement of halogen

From 0 to -1

From -1 to 0

iv.half equation for• Oxidation reaction.

• Reduction reaction

• Write the overall equation

2I- I2 + 2e

Br2 + 2e 2Br-

Br2 + 2I- 2Br- + I2

Question 2

Iron(II) chloride reacts with chlorine in a redox reaction

Name the reaction above

• CHANGE OF IRON(II) ION TO IRON(III) ION

• REDOX (TYPE OF REACTION)

Write out the rough equation first to show the products and the

reactants

2FeCl2 + Cl2 2FeCl3

Place arrows to show oxidation reaction and reduction reaction on your answer on your answer in b)

above

2FeCl2 + Cl2 2FeCl3

reduction

oxidation

What substance is oxidized and why?

• Iron (II) ions, oxidation number of iron

increase from +2 to +3

What substance is reduced and why?

• Chlorine, because oxidation number of chlorine decrease from

0 to -1

Write the half equation for oxidation

Fe2+ Fe3+ + e

Write the half equation for reduction

Cl2 + 2e 2Cl-

Write the overall reaction

2Fe2+ + Cl2 2Fe3+ +

2Cl-

What is the oxidizing agent? And why

Chlorine water,

because it oxidised iron(II) ions to iron(III) ions

What is the reducing agent? And why

Iron(II) ions,

because it reduced chlorine

to chloride ions

State 2 observations in this experiment

• Green solution turns brown

Describe how you would confirm the presence of the product, that is

iron(III) ion

• Add a few drops of NaOH solution, brown precipitate is formed

State another substance that can replace chlorine in the above

experiment

Any oxidising agent

Bromine water //

acidified KMnO4 //

acidified K2Cr2O7

a) Which electrode behave as negative electrode? Why?

- +

3.

a) Which electrode behave as negative electrode? Why?

A because iodide ions undergoes oxidation where it lose electrons,

the electrons are negatively charged causing it to be negative electrode

b) Draw direction for electron flow in the outer circuit

c) Write out the rough equation first to show reactants and the products

d) Put arrows on your equation above to show oxidation reaction and reduction reaction on your answer in c) above

32

272 22 CrIOCrI

OXIDATION

REDUCTION

e) What substance is oxidized? Explain your answer in terms of electron transfer

Iodide ions

because it lose electron

f) What substance is reduced? Explain your answer in terms of electron transfer

Dichromate ions

because it accept electrons

g) Write half equations for:i)Oxidation

ii)Reduction

eII 22 2

OHCr

eHOCr

23

272

72

614

h) Write overall equation

6I- + Cr2O72- + 14H+

2Cr3+ + 7H2O + 3I2

i) State your observations during the experiment ati)Rod A

ii)Rod B

Dark brown solution formed

Orange solution turns to green solution

j)How do you test the presence of iodine formed at rod A?

OR

Add 2 cm3 tetrachloromethane to iodine solution, shake well then purple solution formed at lower layer

Add a few drops of starch solution, a blue-black solution formed

• Test tube C, D. Presence of Fe 2+

• In C and D, silver and lead are less electropositive than iron.

• So,iron nail (Fe) is oxidised to Fe 2+.

• In test tube E, iron nail also

oxidised but takes longer time

After 3 days, which test tubes show blue colour?, why?

Which test tubes show pink colour? Why?

• Test tube A and B.

• Presence of OH-

• Because Mg and Zn are more electropositive than Fe.

• So, Mg atom and Zn atom will lose electrons

• oxygen and water gain these electrons to form OH- This cause the pink colour of phenolphthalein

What is the function of the jelly solution?

• To trap the colour formed during corrosion process

Which of the above metals prevent rusting of iron nails?

• Metals above iron in ECS Magnesium and Zinc metals.

Which of the above metals increase the rusting of iron

• Metals below iron in ECS

• Lead metal and silver metal

Why does the iron surface at the centre of water droplet behave as anode (negative electrode)?

Because here iron atom release electron

Why does the iron surface at the edge of water droplet behave as

cathode( positive electrode)?

• Because oxygen and water gain the electrons here.

What happen at the anode?

• Iron atom loses electron to form iron (II) ions.

• So Oxidation occur.

Write half equation at the anode

Fe Fe 2+ + 2e

Where does the iron(II) ions formed from the reaction go to?

Iron (II) ions dissolve in water

Where does the electrons released by the metal iron go

to?• Electron moves to the edge of

water droplet ( cathode)

What happens at the cathode?

At cathode, electrons are received by oxygen and water molecules to form hydroxide ions

Write half equation at the cathode

• O2 + 2H2O +4e 4OH-

Write equations to form rust when iron(II) ion formed at the anode combine with hydroxide ions formed at the cathode,  • Fe 2+ + 2OH- Fe(OH)2

Fe(OH)2 Fe2O3.xH2O