(a) How does the painting of an iron object prevent its rusting?
(b) How does the electrical conductivity of copper alloys, brass and bronze, differ from that of pure copper?
(c) What is meant by 22 carat gold? Name the metals which are usually alloyed with gold to make it harder.
Answers
a) The painting layer on the iron prevents the physical contact between external iron surface and the atmospheric oxygen. And due to the absence of the physical contact with the atmospheric oxygen,the rust doesn't happen anymore.
b) The amount of electrical conductivity depends upon the physical characteristics of the conducting material. Because, every substance has different amounts of electrical resistivity. And due to different amounts electrical resistivity the electrical conductivity also differs into different substances. This difference of electrical resistance is also applicable for a metal and it's alloy.
c) 22 karat gold means that 22 part of gold is mixed with 2 parts of other types of metals.
The metals like copper , zinc and nickel are added into gold to increase it's physical strength.
Explanation:
a) Iron rust, because it can come in contact with water or moisture, and the metal removes oxygen from the water and forms rust from iron oxide. Varnishes or coatings (such as chromium coatings) prevent H2O particles from entering the metal surface and prevent oxygen absorption. This prevents iron from rusting because it cannot reach water molecules during staining.
(b) The electrical conductivity of copper, brass and bronze alloys differs from that of pure copper. Pure copper has excellent thermal conductivity for all metals sold.
It is resistant to many types of damage, including impacts, abrasion, and corrosion. It also retains its strength after bending, forming and pulling.
(c) Karat is a term used to measure the purity of gold.
The most common alloy metals with gold are copper, nickel, silver, zinc, palladium, manganese and tin.
You can get all the answers of Chapter 3 in the link below:
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