(a) How do we find whether a given element is a non metal, if we know its electronic configuration ? (b) With the help of a reaction show that zinc is more reactive than iron. (c) In nature aluminium is found in combined state whereas silver is found in free state. Give reason. (d) Why should we not throw small pieces of sodium into a sink in the laboratory ? (e) Name any two amphoteric oxides.
Answers
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(a) You know the electronic configuration of an element, hence you know the number of valence electrons (electrons present in outermost shell). If the number of valence electrons is ≤ 3, the element is a metal, otherwise a non metal.
Consider Sodium as an example. Its electronic configuration is 2, 8, 1. In the outermost shell, only 1 electron is present, due to which we can say that it is a metal. In Aluminium, electronic configuration is 2, 8, 3. In the outermost shell, 3 electrons are present, due to which we can say that it is a metal. Now, consider Chlorine, whose electronic configuration is 2, 8, 7. In the outermost shell, 7 electrons are present. Since 7 is not less than 3, we can say that it is a non metal.
(b) We know, that a more reactive metal displaces a less reactive metal from its salt solution.
Take iron chloride (FeCl₂) solution, and Zinc (powdered).
Zn + FeCl₂ ----> ZnCl₂ + Fe
This proves that Zinc is more reactive than iron, because it displaces iron from iron chloride solution, and results in a white solution of zinc chloride and iron deposit.
However, if you take Iron and Zinc chloride solution, there is no reaction.
Fe + ZnCl₂ ---> No reaction
(c) In the reactivity series of metals, aluminium is placed much above, whereas silver is below. Hence, Aluminium is a reactive metal, due to which it readily combines with anything present on earth, whereas silver, being inert, does not combine (react) with anything at normal temperature easily. Hence, aluminium is found in combined state, whereas silver, in free state.
(d) Sodium is a very reactive metal (in the reactivity series), it has got the second position. It vigorously reacts with water (even leads to a fire) to form sodium hydroxide and hydrogen gas. So, if you throw small pieces of sodium into a sink, others, without noting, may open the tap. The tap water falls on the pieces, which may lead to a fire, thus causing injuries. So, you must not throw sodium pieces into a sink.
(e) Amphoteric oxides are those oxides which react with both acids and hot, concentrated alkalis to form salt and water. The three amphoteric oxides are aluminium oxide, zinc oxide and lead oxide (choose any two).
ZnO + 2HCl ----> ZnCl₂ + H₂O
ZnO + 2NaOH -----> Na₂ZnO₂ + H₂O
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