# Metals and Non-metals

## Exemplar Problems

Give the formulae of the stable binary compounds that would be formed by the combination of following pairs of elements.

1. Mg and N2

2. Li and O2

3. Al and Cl2

4. K and O2

What happens when

1. ZnCO3 is heated in the absence of oxygen?

Answer: When zinc carbonate is heated in the absence of oxygen, zinc oxide and carbon dioxide are produced.
ZnCO3 ⇨ ZnO + CO2
2. A mixture of Cu2O and Cu2S is heated?

Answer: When a mixture of copper oxide and copper sulphide is heated, pure copper is obtained.
2Cu2O + Cu2S ⇨ 6Cu + SO2

A non-metal A is an important constituent of our food and forms two oxides B and C. Oxide B is toxic whereas C causes global warming

1. Identify A, B and C

Answer: The clue that C causes global warming shows it is carbon dioxide. A is carbon, B is carbon monoxide and C is carbon dioxide.
2. To which Group of Periodic Table does A belong?

Answer: Carbon belongs to Group 14

Give two examples each of the metals that are good conductors and poor conductors of heat respectively.

Answer: Good conductors: Iron and copper

Name one metal and one non-metal that exist in liquid state at room temperature. Also name two metals having melting point less than 310 K (37°C)

Answer: Mercury (metal) and Iodine (non-metal) exist in liquid state at room temperature. Gallium and caesium are metals with melting points less than 310 K.

An element A reacts with water to form a compound B which is used in white washing. The compound B on heating forms an oxide C which on treatment with water gives back B. Identify A, B and C and give the reactions involved.

Answer: A is calcium, B is calcium hydroxide and C is calcium oxide. The involved reactions are as follows:

Ca + 2H2O ⇨ Ca(OH)2 + H2

Ca(OH)2 ⇨ CaO + H2O

CaO + H2O ⇨ Ca(OH)2

An alkali metal A gives a compound B (molecular mass = 40) on reacting with water. The compound B gives a soluble compound C on treatment with aluminium oxide. Identify A, B and C and give the reaction involved.

Answer: Clue from question 42 shows that compound B is sodium hydroxide. Hence A is sodium and C is sodium aluminate.

2Na + 2H2O ⇨ 2NaOH + H2 + Heat

Al2O3 + 2NaOH ⇨ 2NaAlO2 + H2O

Give the reaction involved during extraction of zinc from its ore by

1. Reaction during roasting of zinc ore

Answer: 2ZnS + 3O2 ⇨ 2ZnO + 2SO2
2. Reaction during calcination of zinc ore

Answer: ZnCO3 ⇨ ZnO + CO2

3. A metal M does not liberate hydrogen from acids but reacts with oxygen to give a black colour product. Identify M and black coloured product and also explain the reaction of M with oxygen.

Answer: M is copper and black coloured product is copper (II) oxide.

2Cu + O2 ⇨ 2CuO

An element forms an oxide A2O3 which is acidic in nature. Identify A as a metal or non-metal.

Answer: We know that oxides of non-metals are acidic in nature and A is a non-metal.

A solution of CuSO4 was kept in an iron pot. After few days the iron pot was found to have a number of holes in it. Explain the reason in terms of reactivity. Write the equation of the reaction involved.

Answer: Iron is more reactive than copper. Hence, iron displaced copper from copper sulphate solution. This reaction resulted in formation of holes in the iron pot. The following equation shows this reaction.

CuSO4 + Fe ⇨ FeSO4 + Cu