Corrosion Validation

Question 1

Corrosion

Answer 1

The process by which metals are converted to oxides or other compounds.

Question 2

Anode reaction

Answer 2

Fe(s) -> Fe+2 + 2e-

Question 3

Cathode reaction (acidic)

Answer 3

O2(g) + 4H+ + 4e- -> 2H20

Question 4

Cathode reaction (neutral/basic)

Answer 4

O2 + 2H20 + 4e- -> 4OH-

Question 5

Methods to prevent corrosion/ rusting

Answer 5

1. Coating the iron with a layer of aluminum
2. Application of a surface coating
3. Galvanizing
4. Cathodic protection

Question 6

Coating the iron with a layer of aluminum

Answer 6

Metals such as aluminum form a very tough oxide coating which strongly bonds to the surface of the metal preventing the surface from further exposure to oxygen.

Question 7

Application of a surface coating

Answer 7

Can be metal or non metal. Metal must be less reactive than iron. Non metal must prevent oxygen and water from coming in contact with iron (plastic).

Question 8

Galvanizing

Answer 8

Coating the metal with a layer of zinc. The zinc acts as a physical barrier keeping water and oxygen out, AND can sacrificially oxidized instead of the iron. The more reactive metal acts as the anode.

Question 9

Cathodic protection

Answer 9

Making the iron the cathode of an electrolytic cell. The applied voltage makes the iron negatively charged and so prevents it’s oxidation. The anode is scrap metal/iron.

Question 10

Methods of enhancing corrosion/rusting

Answer 10

• Concentration of electrolyres
• Involvement of water
• Availability of oxygen
• Low pH
• Mechanical stress (bent nail)
• Temperature

Question 11

Presence of a salt/concentration of electrolytes

Answer 11

Rusting increases in the presence of salt or acids because of an increased
concentration of dissolved ions. Corrosion is a redox process that involves electron transfer and
ion movement. The rate of ion transport can be increased if the conductivity of the aqueous
medium increases.

Question 12

Involvement of water

Answer 12

Rusting occurs much more rapidly in moist conditions.

Question 13

Low pH

Answer 13

High H+ concentration speeds up reduction of oxygen and increases corrosion rate.

Question 14

Mechanical stress (bent nail)

Answer 14

Breaks the protective oxide layer and exposes the fresh iron, increasing corrosion.

Question 15

Temperature

Answer 15

Increasing temperature, increases rate of rusting/corrosion.