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Which of the following conditions accelerate the corrosion of metals the most?
Dry air and low temperature
Pure water and sunlight
Moist air and presence of salts or acids
Vacuum and darkness Question ID : 4410091449981 Option 1 ID : 4410095728424 Option 2 ID : 4410095728425 Option 3 ID : 4410095728426 Option 4 ID : 4410095728427 Status : Answered Chosen Option : C
Moist air and presence of salts or acids
Corrosion, particularly rusting of iron, is an electrochemical process that requires both moisture and oxygen. The presence of salts (electrolytes) and acids increases the conductivity of the surface film of water, which significantly speeds up the rate of the electrochemical corrosion reactions.
Corrosion, particularly rusting of iron, is an electrochemical process that requires both moisture and oxygen. The presence of salts (electrolytes) and acids increases the conductivity of the surface film of water, which significantly speeds up the rate of the electrochemical corrosion reactions.
Think of a car rusting much faster in coastal cities than in dry deserts; the salt air near the coast acts like an 'expressway' for the electrical current that powers the rusting process.
SEA: Salt, Electrolyte, Air (moist) accelerates corrosion.
4Fe+3O2тАЛ+xH2тАЛOтЖТ2Fe2тАЛO3тАЛтЛЕxH2тАЛO тАФ The formation of hydrated iron(III) oxide (rust).
Fe(s)тЖТFe2+(aq)+2eтИТ тАФ Oxidation reaction at the anode.
Corrosion acts as an electrochemical cell where oxidation occurs at the anode and reduction at the cathode. Electrons flow through the metal from the anodic site to the cathodic site, while ions move through the thin layer of moisture (electrolyte). Salts like Na┬аCl increase the ionic conductivity of this moisture, allowing current to flow more easily, thus accelerating the anodic dissolution of metal: FeтЖТFe2++2eтИТ.
Corrosion is a spontaneous oxidation process.
Electrolytes decrease the electrical resistance of the path, boosting the corrosion rate.
High humidity provides the necessary medium for ions to migrate.
Pure water alone is less corrosive than water containing dissolved ionic impurities.
Protection of structural steel in marine environments.
Understanding why anti-corrosive coatings are essential in coastal regions.
Dry air (Option A) lacks the electrolyte medium required for ion transfer.
Pure water (Option B) lacks the ionic conductivity provided by salts or acids.
Vacuum (Option D) excludes both oxygen and water, effectively preventing corrosion.
C is correct тАФ Moist air containing salts or acidic pollutants provides the necessary electrolyte and oxygen to facilitate rapid electrochemical oxidation of the metal.
In competitive exams, remember that any substance that increases the ionic strength of the water film (like Na┬аCl or SO2тАЛ from acid rain) will act as a catalyst for corrosion.
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