i) The compounds which are formed by the transfer of electrons from a metal to a non-metal are known as ionic compounds. Ionic compounds are also known as electrovalent compounds.
Examples: NaCl, CaCl2
Melting and boiling points of ionic compounds are high because to break the attraction between the ions, a large amount of energy is needed for that.
ii) Aluminum is more active than iron, yet there is less corrosion of aluminum when both are exposed to air because:
a. Being more reactive, aluminum reacts with oxygen and forms a layer of aluminum oxide.
b. This protective layer prevents the aluminum from reacting with air.
c. Hence, less corrosion takes place.
d. On the other hand, iron is not able to form such layer, hence it gets corroded easily.
iii) Alloying (mixing of metals and non-metals) is a very good method for improving the properties of the metal. By alloying, we can get the desired properties. Solder is an alloy of lead and tin. Solder has a low melting point. Because of the low melting point, a solder helps to balance a good interaction between the two points of lower resistance. Due to this property, solder is used for welding electrical wires together.
iv) It is easier to obtain metal from its oxide, as compared to its sulphides. Therefore, before reduction, the metal sulphides must be converted into metal oxides. The sulphide ores are converted into oxides by heating strongly in the presence of excess air. This process is known as roasting.
The chemical reaction that takes place during roasting of zinc ores can be shown as:
2ZnS + 3O2 + Heat → 2ZnO + SO2
v) Tarnished copper vessels mean copper vessels which have a coating of green carbonate which is basic. To neutralize the effect of the base, an acid is needed. Hence, tamarind juice which is acidic in nature is used to neutralize the effect of tarnished copper vessels.
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