(a) All ores are minerals but all minerals are not ores. Justify.
(b) An iron knife kept in blue copper sulphate solution turns the blue solution into light green. Explain.
(c ) An athlete won a bronze medal in a race competition. After some days, he found that the medal had lost its lustre due to the formation of a greenish layer on it. Name the metals present in the medal. What is the reason for the formation of a greenish layer on its surface ?

Explanation

(a) In the earth's crust, metals are present in the form of minerals and there are more than one mineral for a particular metal. However, metal may not be extracted from all of them. The mineral from which a metal can be profitably and conveniently extracted is known as ore. This clearly means that all ores are minerals but all minerals are not ores. For example, the different minerals of iron are :
`{:("Haematite",:Fe_(2)O_(3),", Limonite",:Fe_(2)O_(3).3H_(2)O.),("Siderite",:FeCO_(3),", Iron pyrites",:FeS_(2).):}`
Iron is extracted from haematite `(Fe_(2)O_(3))`. Haematite mineral is the ore of iron while other minerals are not the ores.
(b) Iron lies above copper in the activity series. This means that iron or iron knife will displace copper from copper sulphate solution. As a result of the reaction, ferrous sulphate will be formed and the solution will be light green in colour.
`{:(Fe(s),+,CuSO_(4)(aq),rarr,FeSO_(4)(aq),+,Cu(s)),("Iron",,"Copper sulphate",,"Ferrous sulphate",,"Copper"),(,," (blue)",," (light green)",,):}`
(c ) The bronze medal is an alloy and the constituting metals are copper and tin.
The loss of lustre by the medal is due to the formation of a coating of green layer. This layer is of basic copper carbonate.