This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Electrochemistry – Corrosion”.
1. Rusting of iron is a type of corrosion.
Explanation: The most common example of corrosion is the rusting of iron. Rust is hydrated ferric oxide, Fe2O3.xH2O. Rust is formed by the reaction of iron and oxygen in the presence of water or air moisture.
2. What is the method of protection of iron by coating it with zinc called?
b) Cathodic protection
d) Anti-rust solutions
Explanation: Rusting of iron is one of the most common forms of corrosion. To prevent iron from rusting, generally, more active metals are coated on it. The metal which is often used for coating iron is zinc (which is more active) and this process is called galvanization.
3. Which of the following statements regarding corrosion is true?
a) Corrosion does not depend on the reactivity of the metal
b) Presence of impurities does not affect the rate of corrosion
c) Strains in metals affect the rate of corrosion
d) Presence of electrolytes does not affect the rate of corrosion
Explanation: More active metals are readily corroded. Presence of impurities in metals enhances the chances of corrosion. Pure metals do not corrode. Corrosion takes place rapidly at bends, scratches, nicks and cuts in the metal. Electrolytes, if present, also increase the rate of corrosion.
4. Magnesium is used as a sacrificial metal to protect iron from rust.
Explanation: Magnesium and zinc are often used as sacrificial metals. Sacrificial protection means covering the iron surface with a layer of metal which is more active (electropositive) than iron and thus prevents the iron from losing electrons and getting oxidised.
5. Which of the following does not cause rusting of iron?
Explanation: Air and moisture accelerate corrosion. The most important factor in atmospheric corrosion, overriding pollution or lack of it, is moisture. Presence of gases like SO2 and CO2 in air catalyse the process of corrosion. Iron, when placed in vacuum, does not rust.
6. Which of the following is not a method of prevention of corrosion?
b) Anti-rust solutions
c) Cathodic protection
Explanation: Galvanization is the process of coating iron with zinc to prevent its oxidation. Anti-rust solutions are alkaline phosphate and alkaline chromate solutions. The alkalinity prevents the availability of hydrogen ions. Cathodic protection is the process of connecting the iron object to be protected to a more active metal either directly or through a wire.
7. Which of the following statements is false?
a) Salt water decelerates the rate of corrosion
b) Magnesium is more active than iron
c) During galvanization, ZnCO3.Zn(OH)2 is formed which prevent further corrosion
d) Anti-rust solutions are used in car radiators to prevent rusting of iron parts of the engine
Explanation: Saline medium has extra salts such as sodium chloride dissolved in water. It has a greater concentration of electrolyte than ordinary medium. The ions present will favour the formation of more electrochemical cells and favour the transfer of hydrogen ions and will thus promote rusting or corrosion.
8. Which of the following is not essential for rusting to take place?
a) Metal (like iron)
Explanation: Rust is a general term for a series of iron oxides, usually, reddish-brown oxides, formed by the reaction of iron with oxygen in the presence of water or moisture. Water is usually present in the form of water vapour and oxygen is always present in the normal atmosphere. The oxygen needs moisture as a catalyst and reactant to accelerate the reaction, so in the absence of moisture, iron won’t rust.
9. Which of the following is the overall reaction of rusting?
a) 2Fe(s) → 2Fe2+ + 4e–
b) O2 (g)+4H+(aq)+4e–⟶2H2O(l)
c) 2Fe(s) + O2(g) + 4H+(aq) → 2Fe2+(aq) + 2H2O(l)
d) H2O ⇌ H+ + OH–
Explanation: 2Fe(s) → 2Fe2+ + 4e– is the reaction that occurs at the anode.
O2 (g)+4H+(aq)+4e–⟶2H2O(l) is the reaction that occurs at the cathode.
2Fe(s) + O2(g) + 4H+(aq) → 2Fe2+(aq) + 2H2O(l) is the overall reaction of rusting.
10. Which of the following metal does not corrode?
Explanation: Magnesium and zinc are highly active. Hence, they corrode at a faster rate than iron. Iron undergoes rusting in the presence of oxygen and moisture. Copper, a noble metal that occurs naturally in its elemental form, is almost totally impervious to corrosion.
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