Give reason
(i)souring of milk is a chemical change
(ii)mixing of iron and sulphur is a physical change but heating this mixture is a chemical change
(i) A chemical change is a change which results in the formation of a new substance with different chemical properties.
Souring of milk is a chemical change because during that process acidification takes place and soured milk is produced. This sour milk has different chemical properties from fresh milk.
(ii) Mixing of iron and sulphur is a physical change because no new substance is formed and both elements retain their chemical properties. But heating the solution produces a new substance (ferrous sulphide) which has different chemical properties.
Souring of milk is a chemical change because during that process acidification takes place and soured milk is produced. This sour milk has different chemical properties from fresh milk.
(ii) Mixing of iron and sulphur is a physical change because no new substance is formed and both elements retain their chemical properties. But heating the solution produces a new substance (ferrous sulphide) which has different chemical properties.