State the reason for the following: (5) a) Aluminium oxide is called an amphoteric oxide. b) An iron strip dipped in a blue copper sulphate solution turns the blue solution pale green. c) Hydrogen gas is not evolved when most metals react with nitric acid. d) Calcium does not occur in free state in nature. e) Sodium and potassium metals are kept immersed under kerosene.
Answers
Explanation:
a) Aluminium oxide is amphoteric in nature as it acts as both acid and base and neutralize the reaction and produce salt and water.
b)As Iron is more reactive than copper, iron displaces copper in copper sulphate solution. The colour of copper sulphate is blue which after displacement turn pale green (colour of iron sulphate solution).
c)Hydrogen gas is not evolved when a metal reacts with nitric acid. It is because HNO3 is a strong oxidising agent. It oxidises the H2 produced to water and itself gets reduced to any of the nitrogen oxides (N2O, NO, NO2).
d)Calcium does not occur in free state as it has incomplete octet in its valence shell and unstable. When it react with atoms, it donates 2 electrons and becomes stable.
e)Sodium and potassium react vigourously with oxygen, carbon dioxide and moisture present in air which may be explosive. Therefore they are stored in kerosene which cut off the air supply.
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Answer:
a).Aluminium oxide is an amphoteric substance, meaning it can react with both acids and bases, such as hydrofluoric acid and sodium hydroxide, acting as an acid with a base and a base with an acid, neutralising the other and producing a salt.
b). The colour of copper sulphate solution changes from blue to pale green when an iron nail is dipped in it because Iron is more reactive than Copper and can displace it from its salt solution.
c). Hydrogen gas is not evolved when a metal reacts with nitric acid. It is because HNO3 is a strong oxidising agent. It oxidises the H2 produced to water and itself gets reduced to any of the nitrogen oxides (N2O, NO, NO2).
d). Calcium cannot exist in its natural state since it's highly reactive and readily reacts with the surrounding elements to form Calcium compounds. For this reason it cannot exist in its natural form but readily reacts with elements in the surrounding to form compounds.
e). Sodium and Potassium are highly reactive metals and react vigorously with the oxygen, carbon dioxide and moisture present in the air such that it may even cause a fire. To prevent this explosive reaction, Sodium is kept immersed in kerosene because Sodium doesn't react with kerosene.
Explanation:
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