Q.:- Classify the following as chemical or physical changes.
(1) cutting of trees
(2) melting of butter in a pan
(3) rusting of almirah
(4) boiling of water to form steam
(5) passing of electric current through water and the water breaking down into hydrogen and oxygen
(6) dissolving common salt in water
(7) making a fruit salad with raw fruits
(8) burning of paper and wood
(1) Cutting of trees is a chemical change since all chemical reactions stop and we cannot get back the original tree from the wooden peaces.
(2) Melting of butter in a pan is a physical change since there is no change in the chemical composition of butter, only the physical state changes from solid to liquid.
(3) Rusting of almirah is a chemical change since during rusting, a new chemical compound called hydrated iron oxide (rust) is formed.
(4) Boiling of water to form steam is a physical change because during this change only changer of state occurs from liquid water to steam (gaseous) without any change in its chemical composition.
(5) Passing of electric energy through water to form hydrogen and oxygen is a chemical change since the properties of hydrogen (combustible gas) and oxygen (supporter of combustion) are altogether different from those of water which is neither combustible nor a supporters of combustion but it actually extinguishes fire.
(6) Dissolution of common salt in water is a physical change since salt can be easily recovered by evaporating water.
(7) Making a fruit salad with raw fruits is a physical change since there is no change in the chemical properties of the fruits but only the physical appearance has changed.
(8) Burning of paper is a chemical change since carbon dioxide, water vapours, smoke and ash which are the products of combustion cannot be converted back into paper or wood by any physical method.