Metals and Non-metals

HOTS Questions for Class 10 Science Chapter 3 Metals and Non-metals

Question 1.
A student has been collecting silver coins and copper coins. One day she observed a black coating on silver coins and a green coating on copper coins. Which chemical phenomenon is responsible for these coatings ? Write the chemical names of black and green coatings ?
Answer:
The phenomenon is known as corrosion. Air contains traces of hydrogen sulphide gas which reacts with silver metal present in the coin to form silver sulphide. It is black in colour.

Similarly, copper present in the coin reacts with oxygen and traces of both carbon dioxide and water vapours present in air to form a green mass. It is chemically basic copper carbonate :

Question 2.
You are provided with three metals : Sodium, magnesium and copper. Using only water as the reactant, how will you identify them ?
Answer:
The metal which reacts violently with cold water and catches fire is sodium.

1. The metal which evolves hydrogen gas upon heating with water is magnesium.
2. The metal which does not react with water even on strong heating is copper.

Question 3.
E is an element amongst copper, zinc, aluminium and iron. It shows following properties :
(a) One of its ores is rich in E₂O₃
(b) E₂O₃ is not attacked by water,
(c) It forms two chlorides ECl₂ and ECl₃. Name the element and justify your answer.
Answer:
The clue for the correct answer is the formation of ECl₂ and ECl₃. This shows that the element E has variable valencies of 2 and 3. Out of the elements listed, only iron exists in divalent and trivalent forms.
(a) The ore rich in Fe₂O₃ is haematite.
(b) Haematite (Fe₂O₃) is not attacked by water.
(c) The two chlorides are : iron (II) chloride or FeCl₂ and iron (III) chloride or FeCl₃.

Question 4.
An element reacts with oxygen to form an oxide which dissolves in dilute hydrochloric acid. The oxide formed also turns a solution of red litmus blue. Is the element a metal or non-metal ? Explain with the help of a suitable example.
Answer:
The oxide of the element is basic as it turns red litmus solution blue. This means that the element is a metal (M). Let the metal be sodium (Na). The chemical equations that are involved are given as follows :

Question 5.
An element E combines with oxygen to form an oxide E₂O which is a good conductor of electricity.
Give the following information:

1. How many electrons will be present in the valence shell of the element E ?
2. Write the formula of the compound formed when the element E combines with chlorine.

Answer:

1. From the formula E₂O of the oxide, it is clear that the valency of the element E is one. This means that it has only one electron in the valence shell.
2. We know that chlorine is monovalent. Sine the valency of the element E is a also one, the formula of the chloride of the element is ECl.

Question 6.
An element A’ catches fire in water and burns with golden yellow flame in air. It reacts with another element ‘B’, present in group 17 to give a product ‘C’. An aqueous solution of product ‘C’ on electrolysis gives a compound ‘D’ and liberates hydrogen. Identify A, B, C and D.
Answer:
Since the element A’ catches fire in water and burns with golden yellow flame, it is sodium (Na). The element ‘B’ with atomic number 17 is chlorine (Cl). Both these combine to form sodium chloride (NaCl) which is designated as ‘C’. Upon electrolysis, sodium chloride gives sodium hydroxide (D) and evolves hydrogen along with chlorine.