Ores: The minerals form which metals can be extracted easily and economically are called ores for example Haematite is ore of iron.
Alloy: The homogeneous mixture of two or more metals or may be the metals with non metals is called alloy. Example: brass is an alloy of copper and zinc.
Rusting: Iron reacts with oxygen in the presence of water to form reddish brown colored hydrated iron oxide called rust. It is the slow oxidation of iron. Its chemical formula is Fe2O3.XH2O
Aqua-regia: It is a mixture of conc. Hydrochloric acid and conc. Nitric acid in the ratio of 3:1 by volume. It is used to dissolve of gold.
Ores of metals:
Iron: Haematite, Magnetite, Iron Carbonate
Aluminium: Bauxite, Felspar
Copper: Copper pyrite or Chalcopyrite, Chalcite or copper glance
Silver: Argentite, Silver copper glance , Horn Silver
Gold: Alluvial soil, Calverite
Reactions of metals with acids:
Rection metals with Hydrochloric acid:
Metal+HCl Metal Chloride+H2
With dil Sulphuric acid:
Metal + H2SO4 Metal Sulphate + H2
With Conc. Sulphuric acid:
Metal + conc H2SO4 Metal Sulphate + H2O+SO2
With dilute Nitric acid:
Metal + dil. HNO3 Metal Nitrate + NO+H2O
Except Iron: 4Fe + dil. 10HNO3 4Fe(NO3)2+NH4NO3+3H2O
Aluminium doesnot reacts with nitric acid at all.
With conc. Nitric Acid:
Metal + conc. HNO3 Metal Nitrate+H2O+NO2 (applicable for Iron also.)
Reaction of gold with aqua-regia:
1. Though aluminum is a quite reactive metal, it does not react with water.
Ans- Due to the presence of an inert aluminum oxide layer on its surface which is formed when aluminum combines with the oxygen of air. This thin but strong layer prevents the reaction of aluminum with water.
2. Nitric acid can be transported and stored in aluminum vessels.
Ans- Nitric acid is an oxidizing agent, so it forms and oxide layer on the surface of aluminium meta. This oxide layer prevents the further action. As a result, nitric acid cannot react with aluminium. So nitric acid can be transported and stored in aluminium vessels.
3. Aluminium vessels cannot be used for storing alkali solutions.
Ans- Aluminium vessels cannot be used for storing alkali solutions (like NaOH, KOH) because alkalis react with the aluminium metal of the vessel to from soluble compounds which eat up the vessel gradually.
4. Aluminium metal is used in making bodies and parts of aeroplane.
Ans- Aluminium metal is used in making bodies and parts of aeroplane because of the following reasons:
– Aluminium is lighter than iron.
– Aluminium reacts with moist air to form aluminium oxide since aluminium oxide forms thin and hard layer on its surface. Air and water have less effect on it.
5. Aluminium is used for making silver paints and mirrors.
Ans- Aluminium is used for making silver paints and mirrors because of its silvery appearance. Since Aluminium is a good reflector, it is deposited on glass to make mirrors.
6. Gold is found in pure state in nature but not the iron.
Ans- Gold is a noble metal. It does not react with air, water, acids and other chemicals in normal condition of temperature and pressure. So gold is found in pure state. But iron combines with air, acids and other chemicals in ordinary condition to form various types of compounds. So iron is not found in pure state in nature.
7. Iron is generally extracted from hematite.
Ans- Iron is generally extracted from hematite because it contains maximum amount of iron (about 72.5%)
8. Metals are good conductor of heat and electricity.
Ans- Metals are good conductor of heat and electricity due to presence of free electrons.
9. Aluminium is a very reactive metal but does not react with the food.
Ans- Aluminium does not react with air, water, oxygen and chemicals present in food at ordinary temperature. Hence, aluminium does not react with food.
10. HCI is kept in a glass or plastic container but not in a container made up of aluminium.
Ans- Glass or plastic does not react with HCL but aluminium reacts with HCI to form aluminium chloride.
11. The copper, silver and gold are called coinage metals.
Ans- As copper, silver and gold are used for making coins and decorative purposes; they are called as coinage metals.
12. Dil. H2SO4 is placed in the container made of silver but conc. H2SO4 is not.
Ans- Silver does not react with Dil. H2SO4 but reacts with conc. H2SO4 is placed in the container made of silver but conc. H2SO4 is not.