Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Corrosion is a process where metals are gradually worn away by the action of air, moisture, or chemicals (like acids) on their surface.
Silver articles become black after some time when exposed to air because silver reacts with sulfur in the air to form a coating of silver sulphide ().
Copper reacts with moist carbon dioxide in the air and slowly loses its shiny brown surface and gains a green coat. This green substance is basic copper carbonate ().
Iron when exposed to moist air for a long time acquires a coating of a brown flaky substance called rust ().
Both air (oxygen) and moisture (water) are essential conditions for the rusting of iron.
Prevention of corrosion can be achieved by painting, oiling, greasing, galvanising, chrome plating, anodising, or making alloys.
Galvanisation is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc (). The galvanized article is protected even if the zinc coating is broken.
Alloying is a very good method of improving the properties of a metal. An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal. For example, Iron () mixed with Nickel () and Chromium () gives stainless steel, which is hard and does not rust.
If one of the metals in an alloy is mercury (), then the alloy is called an amalgam.
📐Formulae
💡Examples
Problem 1:
Explain why a copper vessel loses its shine and acquires a green coating when exposed to air.
Solution:
Copper reacts with the moist carbon dioxide () present in the air to form basic copper carbonate ().
Explanation:
The formation of this green layer of basic copper carbonate covers the shiny brown surface of the copper metal, leading to the loss of its characteristic metallic luster.
Problem 2:
An iron nail is placed in a test tube containing anhydrous calcium chloride (). Will it rust?
Solution:
No, the iron nail will not rust.
Explanation:
Anhydrous acts as a drying agent and absorbs any moisture present in the air inside the test tube. Since rusting requires both oxygen and moisture, the absence of moisture prevents the chemical reaction .
Problem 3:
Define an alloy and give the composition of Brass and Bronze.
Solution:
An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal.
- Brass:
- Bronze:
Explanation:
Alloying changes the physical properties like electrical conductivity and melting point. For instance, Brass and Bronze are not as good conductors of electricity as pure copper ().