WORKSHEET 1, PHYSICAL AND CHEMICAL CHANGES, CLASS 7

1. Classify the following changes as physical or chemical changes – 

     (i) Burning of sugar

     (ii) Melting of butter

     (iii) Souring of milk 

     (iv) Drying of wet hair 

     (v) Mixing lime with water 

     (vi) Burning of coal 

     (vii) Growth of plants to trees 

     (viii) Spoiling of food 

     (ix) Bursting of crackers 

     (x) Cutting of vegetables 

Q.2. Name the following: 

    (i) Common name of copper sulphate. 

    (ii) The gas evolved when vinegar is reacted with baking soda. 

    (iii) Any 3 alloys from your daily life.

    (iv) Two factors which cause rusting. 

    (v) An example of a chemical change in which there is a change of colour. 

Q.3. Metal X burns with a dazzling white flame to form a compound Y. Compound Y reacts with water to form Z which in turn turns red litmus paper blue. 

   (i) Identify X, Y and Z 

  (ii) Write down the chemical reactions involved. 

Q.4. Metal A change the colour of copper sulpahte solution when added to it. 

   (i) Name metal A. 

   (ii) Write down the reaction involved in this change. 

   (iii) What type of change is this?

Q.5. Complete the following reactions – 

   (i) __________ + Carbon dioxide ➡️Calcium carbonate + __________.

   (ii) Carbon + oxygen➡️ _____________ 

   (iii) Magnesium oxide + _____________➡️ Magnesium hydroxide.

   (iv) Magnesium + _____________ ➡️Magnesium oxide.

Q.6. Fill in the blanks: 

   (i) Dissolving sugar in water is a ___________ change. 

   (ii) The process of depositing a layer of zinc on iron is called ____________.

   (iii) Crystals of pure substances are obtained from their solutions by __________.

    (iv) Hydrated iron oxide is called ___________

Q.7.Which of the following is a physical but irreversible change? 

   (a) burning of a matchstick 

   (b) melting of an ice cream 

   (c) crushing of glass 

   (d) lighting of an electric bulb

Q.8. Observe the following two changes. Change A: Biogas is produced by decomposition of animal and plant waste by anaerobic bacteria. Change B: Biogas is burnt as other fuels. Which of these is a chemical change?

    (a) Change A 

    (b) Change B  

    (c) Both (a) and (b)

    (d) None of these