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

Question: What is corrosion? How does it affect different metals?

Answer: Corrosion is defined as attack of atmospheric gases and moisture on the surface of metal  making them deformed and weak. It iron is left in open for a period of time, it slowly gets deposits of brown flakes on it, which is called rusting of iron. It is undesirable because it makes the iron weak and eat it up slowly with passage of time. Similarly silver objects become black in color and loose their lustree as silver react with hydrogen sulphide gas of air. Slowly the copper vessels also get coated with greenish layer of copper carborate. It is formed due to reaction of copper with carbondioxide of air and water vapor also present in air.

2Cu         +         H₂O         +        CO₂            +          O₂           →           Cu(OH)₂             +             CuCo_{3
                                                                                                                                            Copper hydroxide                  Copper carbonate}

Question: Write composition, properties and uses of following alloys: Steel, Stainless steel, Brass and Duralumin.

Answer: