(A) Samarth brought an iron pipe but forgot to use it. After 2 months he observed that the surface of the pipe was covered with red coloured flaky substance and even red coloured powder was collected where the pipe was kept.
His friend Sumit asked him to rub that pipe with a sandpaper and then to colour it.
Why was the metal pipe changed to red in colour? Why did Sumit advise Samarth to colour that pipe?
(B) Rupali bought silver jewellery and she used it regularly. After some days, jewellery lost its shine and became black in colour. Her friend Swapna advised her to clean it with toothpaste.
Why does silver jewellery turn black after use? How does toothpaste clean the silver jewellery?
Ans. (B) Silver jewellery turns black as a result of reactions with sulphur-containing chemicals in the air forming silver sulphide . Using mild abrasives, toothpaste helps clean silver jewellery by mechanically removing black tarnish (silver sulphide) and exposing the brilliant silver surface.