Corrosion of metals and Statue of Liberty

Question 1

What is corrosion?

Accepted Answer

Corrosion is the process in which metals are gradually eaten up by the action of air, moisture, or chemicals on their surface.

Question 2

Why do silver articles turn black after some time?

Accepted Answer

Silver reacts with hydrogen sulphide ($	ext{H}_2	ext{S}$) gas present in air to form a black coating of silver sulphide ($	ext{Ag}_2	ext{S}$).

Question 3

Copper reacts with moist gas 'A' present in the air and slowly loses its shiny surface. It turns green. Identify 'A' and the substance of green coating formed on the surface of copper.

Accepted Answer

Gas 'A' is **Carbon dioxide** ($	ext{CO}_2$) along with moisture/oxygen. The green coating is **Basic Copper Carbonate** [$	ext{CuCO}_3\cdot	ext{Cu(OH)}_2$].

Question 4

**OR** What is an alloy? How is an alloy made?

Accepted Answer

An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal. It is made by melting the primary metal first, dissolving the other elements in it in definite proportions, and then cooling the mixture to room temperature.

Corrosion of metals and Statue of Liberty

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