NCERT 8th Class (CBSE) Science: Metals And Non-Metals

Question: Give the important uses of copper.

Answer: Important uses of copper:

1. Copper is widely used to make electric wires and cables. Copper coils are used in several electrical appliances.
2. It is also used to make heating utensils, car radiators and calorimeters.
3. It forms useful alloys.

Question: Aluminium protects itself against corrosion. Discuss why it necessary to anodize aluminium to make it corrosion resistant.

Answer: A layer of aluminium oxide is formed on aluminium upon exposure to air. This prevents further corrosion of aluminium. If this layer layer is made more uniform, it protects the aluminium underneath more effectively. This is done by a process called anodizing. It consists of passing an electric current through sulphuric acid using aluminium as anode. Oxygen is evolved at the anode which reacts with aluminium to form a uniform protective layer of aluminium oxide.

Question: List important uses of hydrogen.

Answer: Important uses of hydrogen:

1. Hydrogen is used for the manufacture of ammonia gas, which is used to manufacture fertilizers such as urea and ammonium sulphate.
2. It is used in the extraction of metals such as copper, lead and tin.
3. Oxy-hydrogen flame, obtained by burning hydrogen in oxygen is used for cutting and welding metals.
4. Hydrogen is considered to be non-polluting fuel of the future. Considerable amount of research is being carried out to use it efficiently as a fuel.

Question: List important uses of Silicon.

Answer: Important uses of Silicon:

1. Silicon is extensively used in the electronic and computer industries to make devices, such as transistors, microchips and solar cells.
2. It is used to manufacture silicones, which are used for making waterproof clothes, greases and polishes, and insulating material for electrics

Question: State whether a displacement reaction will occur if the following are mixed. Give reasons. Give the reaction.

Answer: Displacement Reaction: A more reactive metal displaces a less reactive metal from its salt solution. When a more reactive metal is placed in the salt solution of a less reactive metal,then the more reactive metal displaces the less reactive metal from its salt solution.

1. Copper sulphate and Zinc: When a strip of zinc metal is placed in a copper sulphate solution for sometime, then the blue colour of copper sulphate solution fades and a red-brown coating of copper metal is deposited on the zinc strip.CuSO4 (aq)    +       Zn (s)   —->  Cu (s)    +    ZnSO4 (aq)

   A more reactive metal zinc is displacing a less reactive metal copper from its salt solution, copper sulphate solution.The blue colour of copper sulphate solution gradually disappears due to the formation of zinc sulphate. The copper metal produced in this displacement reaction forms a red-brown coating over the zinc strip.A less reactive metal cannot displace a more reactive metal from its salt solution.

   Cu (s) + + ZnSO4 (aq) —–> no reaction

2. Copper sulphate and iron: When a strip of iron metal is placed in a copper sulphate solution for sometime,then the blue colour of copper sulphate solution fades and a red-brown coating of copper metal is deposited on the iron strip.Fe (s) + CuSO4 (aq) ——> FeSO4 (aq) + Cu (s)Grey         Blue                        Greenish soln     Red-brown

   The solution turns greenish due to the formation of iron sulphate.A more reactive metal iron is displacing a less reactive metal copper from its salt solution,copper sulphate solution.The blue colour of copper sulphate solution changes to greenish due to the formation of iron sulphate.The copper metal produced in this displacement reaction forms a red-brown coating over the iron strip.A less reactive metal cannot displace a more reactive metal from its salt solutionFeSO4 (aq) + Cu (s) ——–>No displacement reaction

   Displacement reaction does not occur because copper metal is less reactive than iron metal.So a less reactive metal copper cannot displace a more reactive metal iron from its salt solution,iron sulphate solution.

3. Iron sulphate and zinc: When a strip of zinc metal is placed in iron sulphate solution,then a displacement reaction take place to form zinc sulphate solution and iron metal.FeSO4 + Zn ———-> ZnSO4 + Fe

   Zinc metal displaces iron metal from iron sulphate solution.This displacement reaction takes place because zinc is more reactive than iron.