Question

Many pure metals like copper, iron and gold are very soft and as such are considered unsuitable for certain uses. Metallic objects around us such as cooking utensils, statues, ornaments, guns, etc., are actually not made up of pure metals. Instead of pure metals, alloys are used in the design of most of the useful objects. Making alloys enhances the basic properties of a metal which is the primary constituent (metal) of an alloy.

1. How does electrical conductivity and melting point of a metal change when it is converted to its alloy by mixing a small amount of an element in it?   (1)
2. Name an alloy used for welding two wires together in an electric circuit. Write its major constituents.   (1)
3. 1. What are alloys? How is ‘Brass’ (an alloy) prepared?   (2)
      OR
   2. What is stainless steel? How is it prepared? Write one important property which makes it more useful in making cooking utensils as compared to its primary metal.   (2)

Answer 1

1. • When a pure metal is converted into an alloy by mixing a small amount of another element, its electrical conductivity decreases because the added element disturbs the orderly arrangement of metal atoms, restricting the free movement of electrons.
   • The melting point of the alloy is usually lower than that of the pure metal because the presence of different atoms weakens the metallic bonds.
2. • Solder is an alloy used for welding two wires together in an electric circuit.
   • The major constituents are Lead (Pb) and Tin (Sn).
3. 1. • Alloys are homogeneous mixtures of a metal with one or more other metals or non-metals, prepared to enhance the properties of the base metal.
      • Brass is an alloy made by mixing Copper (Cu) and Zinc (Zn).
        OR
   2. • Stainless steel is an alloy of Iron (Fe), Chromium (Cr), Nickel (Ni), and Carbon (C).
      • It is prepared by adding Chromium and Nickel to iron, which prevents rusting.
      • Important Property: Stainless steel is highly resistant to corrosion, making it more useful for making cooking utensils than iron, which rusts easily.