## Topic outline

• ### Materials: Metals and Non-Metals

##### Q67. Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.(a) How will she find the nature of the gas?(b) Write down word equations of all the reactions taking place in this process.

Ans. (a) Add a few drops of water in the test tube containing gas. Now, cover the test tube and shake well. After shaking, test the solution with blue litmus and red litmus. It will turn blue litmus red. Thus, the gas is acidic in nature.

(b) Charcoal reacts with oxygen to form carbon dioxide gas.

C (carbon) + O2 (oxygen) CO2 (Carbon dioxide)

Carbon dioxide reacts with water to form carbonic acid, which turns blue litmus paper red

CO2 (Carbon dioxide) + H2O (Water) H2CO3 (Carbonic acid)

##### Q68. When an iron knife is kept dipped in blue copper sulphate solution the solution changes to light green. Why?OrWhat happens when a piece of iron metal is placed in copper sulphate solution name the type of reaction involved?

Ans. When iron is placed in copper sulphate solution for some time, then the blue colour of copper sulphate solution fades and a red-brown coating of copper metal is deposited on the piece of iron. This reaction can be written as:

Copper sulphate(CuSO4) + Iron(Fe) Iron sulphate(FeSO4) + copper(Cu)

Blue solution                                  Greenish solution

Here, the solution turns greenish due to the formation of iron sulphate. In this reaction, a more reactive metal ‘iron’ is displaces a less reactive metal ‘copper’ from its salt solution, copper sulphate solution.

##### Q69. Explain how metals and non-metals produce oxides with different characteristics.

Ans. Metal

When magnesium burns in air, it combines with the oxygen of air to form magnesium oxide (which is basic in nature).

Magnesium(Mg) + Oxygen(O2) Magnesium oxide(MgO)

(A basic oxide)

Magnesium oxide dissolves partially in water to form magnesium hydroxide solution.

Magnesium oxide(MgO) + Water(H2O) Magnesium hydroxide[Mg(OH)2]

Magnesium hydroxide turns red litmus blue. This shows that it is a base and magnesium oxide is a basic oxide.

Non- Metal

When sulphur burns in air, it combines with oxygen of air to form sulphur dioxide (which is an acidic oxide).

Sulphur(S) + Oxygen(O2)   Sulphur dioxide(SO2)

(An acidic oxide)

Sulphur dioxide dissolves in water to form sulphurous acid solution.

Sulphur dioxide(SO2) + Water(H2O) Sulphurous acid(H2SO3)

This sulphurous acid turns blue litmus to red showing that it is an acid and that sulphur dioxide is acidic in nature.