Activity 2.10 NCERT Class 9 Science Chapter 2 Is Matter Around Us Pure
Activity 2.10 asks us to heat iron with sulphur and see their magnetic and chemical behaviour.
Iron forms iron sulphide on heating with sulphur.
Addition of carbon disulphide to iron sulphide does not have any change.
Iron sulphide reacts with dilute acid and produces hydrogen gas.
This experiment wants us to understand the difference between a mixture and a compound. A mixture formation is a physical phenomenon which does not include any chemical reaction. When two elements or molecules react and from product different from the reactant, the product is called a compound.
Here, the mixing of iron filings with sulphur does not cause any reaction. They are a mixture. When we heat both the substance, they react with each other and form iron sulphide. This is a compound formation.
During this chemical reaction free electrons in the outer shell (valance shell) of iron form covalent bonds with the electrons of sulphur. Free electrons are necessary for magnetic property. As a result, iron sulphide does not show magnetic property like iron.
Metal salts react with acids and displace the hydrogen atom. This produces hydrogen gas.
Simple mixing of two or more substances is different from a reaction. Former forms a mixture while later forms a compound. A mixture retains the property of its components. While the components of a compound lose its individual properties.
(Refer to Chapter 2).