VII. Corrosion of Metals Any metal corroding is simply that metal being oxidized. The result is often the formation of metallic oxides.

eg: CuO Turquoise color of the roof of the Hotel Vancouver and Statue of Liberty)

eg: Formation of rust

Fe Fe2+ + 2e-

H2O + ½O2 + 2e- 2OH-

Fe + H2O + ½O2 Fe(OH)2

Fe(OH)2 + H2O + ½O2 Fe(OH)3

Fe(OH)3 Fe2O3 + 3H2O

“Rust” is both Fe2O3 and Fe(OH)3

Step 1

Step 2

Step 3Sun

Note: Never store different metals in contact with each other… One metal will speed up corrosion of the other.

eg:

H2OFe Fe2+ + 2e-

Cu2+ + 2e- Cu

CuO + H2O Cu(OH)2

The presence of the Cu speeds up the oxidation of the iron (a simple electrochemical cell has been created)

then…

Fe Cu

This technique could be used to protect the Cu from oxidizing if you don’t care about losing Fe.(Cathodic protection)

Preventing Corrosion: Paint surface. Galvanize: use a thin layer of zinc to protect underlying metal.

eg: galvanized nails are iron or steel nails dipped in molten zinc.

Cathodic protection: one metal is sacrificed to protect another.

eg: strips of zinc are used to protect iron hulls of ships. The zinc is more easily oxidized than the iron.(As zinc strips breakdown they are replaced)

VIII. Redox Titrations One substance is used to determine concentration of

another.eg: MnO4- + 8H+ + 5Fe2+ Mn2+ + 4H2O + 5Fe3+

Purple Colourless

If 27.4mL of 0.020M KMnO4 is used to titrate 25.0mL of a solution of Fe2+, what is the concentration of Fe2+?

Moles of MnO4-:

0.0274L 0.020molL

= 5.5x10-4mol

Moles of Fe2+:

5.5x10-4mol MnO4- 5 mol Fe2+

1 mol MnO4-

= 2.7x10-3mol

[Fe2+] = 2.7x10-3mol0.025L

= 0.11M

IX. Breathalyser Function Redox reaction is used.

Orange GreenCH3CH2OH + Cr2O7

2- + 8H+ CH3CH + 2Cr3+ + H2O

O

Alcohol (CH3CH2OH) from breath reacts with Cr2O72-

The more alcohol that is present, the more Cr3+ is produced and reaction goes from orange to green.(monitored by computer)