1. Why the surface of some metals acquires a dull appearance when exposed to air for a long time.
2.Why Sodium is kept immersed in kerosene oil.
3. Why a salt which does not conduct electricity in the solid state becomes a good conductor in molten state.
4.Why Ionic compounds have generally high melting points.
5.Why An iron grill is painted frequently.
6. Why is aluminum extracted from alumina by electrolytic reduction and not by reducing with carbon?
7. Why Aluminum is a highly reactive metal, still it is used to make utensil for cooking.
8. Why Platinum, gold and silver are used to make jewellery.
9. Why Sodium, potassium and lithium are stored under oil.
10.Why Zinc metal can displace copper from copper sulphate solution but copper cannot displace zinc from zinc sulphate solution.
11.Why is it that aluminium which is more reactive than iron dies not corrode like iron?
12. Why are carbonate and sulphide are usually converted into oxides during the process of extraction. Solution
1. When the surface of some metals exposed to air for a long time acquires a dull appearance because it form thin layer oxide , carbonate and oxide on their surface
2. Sodium is kept immersed in kerosene because it reacts so vigorously that they catch fire when kept in the open. Hence to protect them and to prevent accidental fires, they are kept immersed in kerosene.
3. Salt is composed of positive sodium ions and negative chloride ions. In solid these ions are arranged with great force of attraction and unable to move. So in melted state its ions become free to move and conduct electricity.
4. Ionic compounds have high melting and boiling points because a considerable amount of energy is required to break the strong inter-ionic attraction. Ionic compounds form crystals.[ These crystals are basically just great big blocks of positive and negative charges all stuck together. ]
5. An iron grill is painted frequently to prevent it from rusting. Iron when exposed to moist air for a long time acquires a coating of a brown flaky substance called rust.
6. Aluminium was discovered by Oersted in 1825. It is the most abundant metal in the earth crust. Aluminium is a reactive metal and so does not occur free in nature Aluminium oxide due to its great affinity for oxygen is a very stable compound. It is not reduced easily by common reducing agents like carbon, carbon monoxide or hydrogen.. Hence, electrolytic reduction was chosen as the method for reducing alumina.
7. Aluminum is a highly reactive metal, still it is used to make utensil for cooking because it is conductors of heat, have high melting points malleable , ductile and less corrosive
8 Platinum, gold and silver are used to make jewellery because of their malleability and ductility.
9. Sodium, potassium and lithium are highly reactive metals so they are stored under oil because they catch fire if kept in the open or react violently if kept in cold water .
10. Zinc metal can displace copper from copper sulphate solution but copper cannot displace zinc from zinc sulphate solution as zinc is more reactive than copper.
11. Aluminum which is more reactive than iron does not corrode like iron because as aluminum react with air and moisture form layer of aluminum oxide that seals out oxygen and no more oxidation will take place and aluminium corrode slowly than iron.
12. Carbonate and sulphide ores are are usually converted into oxides during the process of extraction. because their direct reduction to obtain metals is not possible so It is easier to obtain a metal from its oxide as compared to its sulphides and carbonates