Question 1 Page 24 (Right Side) - Chapter 2 Class 9 - Is Matter Around Us Pure

Classify the following as chemical or physical changes:

• cutting of trees,
• melting of butter in a pan,
• rusting of almirah,
• boiling of water to form steam,
• passing of electric current, through water and the water breaking down into hydrogen and  oxygen gases,
• dissolving common salt in water,
• making a fruit salad with raw fruits, and
• burning of paper and wood

Answer

• Cutting of trees - Physical change
  (During cutting of trees no new substance is formed, hence its a physical change)

• Melting of butter in a pan - Physical change
  (It is a physical change  because it is a change of state of matter from solid to liquid
  This change is temporary and can be reversed)

• Rusting of almirah - Chemical Change
  (Rusting is a chemical reaction in which iron reacts with oxygen to form a new substance called rust (Ferric Oxide), hence its a chemical change)

• Boiling of water to form steam - Physical Change
  (It is a physical change  because it is a change of state of matter from liquid to gas.
  This change is temporary and can be reversed)

• Passing of electric current, through water and the water breaking down into hydrogen and   oxygen gases - Chemical Change
  (Passing current in water breaks it into Hydrogen and Oxygen, hence new substances are formed. Therefore, its a chemical change)

• Dissolving common salt in water - Physical Change
  (It is a physical change because this change can be reversed to get back salt and water
  This can be done by heating salt solution and water.
  Water will convert into water vapour and we can get salt at the bottom of container)
  
  

• Making a fruit salad with raw fruits - Physical Change
  (It is a physical change because no new substances are formed)
  
  

• Burning of paper and wood -
  (It is a chemical change because when we burn paper and wood, new substances are formed like carbon and smoke. This change cannot be reversed)