Question

Corrosion of silver occurs due to the formation of

• A. Ag₂O
• B. AgCl
• C. Ag₂CO₃
• D. Ag₂S

Answer 1

The correct option is D

Ag₂S

Corrosion of Silver

The reaction of metals with gases present in the atmosphere is called corrosion. The atoms of metal on the metal surface reacts with atmospheric gases like Carbon dioxide (CO₂), Sulphur dioxide (SO₂), Oxygen (O₂), Water vapour (H₂O) etc. to cause the gradual deterioration of metals.

Silver (Ag) reacts with Sulphur (S) and other Sulphur containing compounds like Hydrogen sulphide (H₂S) in air to form Silver sulphide (Ag₂S) which is a black solid making the silver black. The reaction requires Oxygen (O₂) which is available in air.

The chemical equation for the corrosion reaction is:

$4Ag\left(s\right)+O_2\left(g\right)+2H_{2}S\left(g\right)\to 2A{g}_{2}S\left(s\right)+2H_{2}O\left(g\right)$

(Silver) (Oxygen) (Hydrogen (Silver (Water vapour)

sulphide) sulphide)

Silver sulphide is formed in preference to Silver oxide (Ag₂O) due to the affinity of Sulphur (S) toward Silver.

(D) From the balanced equation for the corrosion of Silver due to Hydrogen sulphide, it can be seen that the black precipitate of Silver sulphide causes corrosion in Silver. Silver sulphide results in the formation of black fissures or pits in metal. Therefore, option (D) is correct.

(A) Silver oxide (Ag₂O) does not cause corrosion in Silver. Therefore, option (A) is incorrect.

(B) Silver Chloride (AgCl) is not formed by the reaction of silver with atmospheric gases. Therefore, option (B) is incorrect.

(C) Silver carbonate (Ag₂CO₃) does not cause corrsion of silver. Therefore, option (C) is incorrect.

The correct option is (D) Ag₂S.