Chemistry
Give a reason why –
(a) rust turns moist red litmus blue
(b) a green deposit is seen on the surface of an article of copper
(c) iron objects rust easily but the iron pillar at Qutab Minar has not rusted over the years.
Answer
(a) Rust is hydrated iron [III] oxide. As all metallic oxides are basic in nature and rust is a metallic oxide of iron, hence, it turns moist red litmus blue.
(b) The green deposit on copper articles is caused by copper reacting with moisture and atmospheric gases to form copper carbonate (CuCO3), which is green, and copper hydroxide (Cu(OH)2).
(c) Iron pillar of Qutab Minar has not rusted over the years because
- The high purity and great mass of iron may have created a temperature stabilizer thus reducing the condensation of moisture on it.
- The protective passive iron coating formation on the surface of iron.
- Good forge welding and absence of impurities in iron.
Related Questions
Give a reason why oiling or greasing is done on the exposed moving iron parts of machinery and not preferred on heavy stationary iron parts.
State why galvanization, tinning and chromeplating are used as three different processes for coating specific articles for prevention of rusting.
State a specific reason for using –
(a) steel in automobiles
(b) gold in jewellery
(c) copper in electrical cables
(d) zinc in galvanizing
(e) lead in bullets
(f) magnesium in fireworks.
Complete the statements given below, by filling in the blank with the correct word/s:
The ability of a metal to produce a resonant sound …………… [ductility/sonority/malleability].
A metal which floats on water …………… [zinc/potassium/magnesium].
A non-metal that leaves a mark on paper …………… [phosphorous/graphite/sulphur].
A non-metal which allows an electric current to pass through it …………… [graphite/sulphur/iodine].
A non-metal added to swimming pools to kill germs …………… [nitrogen/chlorine/oxygen].