Chapter 5 Solutions — Changes Around Us: Physical and Chemical

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1. 1.
   Which of the following statements are the characteristics of a physical change?

   • (i) The state of the substance may or may not change.
   • (ii) A substance with different properties is formed.
   • (iii) No new substance is formed.
   • (iv) The substance undergoes a chemical reaction.
   • (a) (i) and
   • (ii) (b)
   • (ii) and
   • (iii) (c)
   • (i) and
   • (iii) (d)
   • (iii) and (iv)
2. 2.
   Predict which of the following changes can be reversed and which cannot be reversed.

   • (i) Stitching cloth to a shirt
   • (ii) Twisting of straight string
   • (iii) Making idlis from a batter
   • (iv) Dissolving sugar in water
   • (v) Drawing water from a well
   • (vi) Ripening of fruits
   • (vii) Boiling water in an open pan
   • (viii) Rolling up a mat
   • (ix) Grinding wheat grains to flour
   • (x) Forming of soil from rocks
3. 3.
   State whether the following statements are True or False. In case a statement is False, write the correct statement.

   • (i) Melting of wax is necessary for burning a candle.
   • (ii) Collecting water vapour by condensing involves a chemical change.
   • (iii) The process of converting leaves into compost is a chemical change.
   • (iv) Mixing baking soda with lemon juice is a chemical change.
4. 4.
   Fill in the blanks:

   • (i) Nalini observed that the handle of her cycle has got brown deposits. The brown deposits are due to ________, and this is a ________ change.
   • (ii) Folding a handkerchief is a _________________ change and can be ________.
   • (iii) A chemical process in which a substance reacts with oxygen with evolution of heat is called _________, and this is a __________ change. (iv)…
5. 5.
   Are the changes of water to ice and water to steam, physical or chemical? Explain.
6. 6.
   Is curdling of milk a physical or chemical change? Justify your statement.
7. 7.
   Natural factors, such as wind, rain, etc., help in the formation of soil from rocks. Is this change physical or chemical and why?
8. 8.
   Read the story 'Eco-friendly Prithvi' and tick the most appropriate option(s): Prithvi chops vegetables, peels potatoes, and cuts fruits (physical changes/chemical changes). He collects the seeds, fruits, and vegetable peels into a clay pot (physical change/chemical change). The fruits, vegetable peels, and other materials begin to decompose due to the action of bacteria and fungi, forming…
9. 9.
   Sort the following changes: write physical changes in area 'A', chemical changes in area 'B', and changes that are both physical and chemical in area 'C'. Changes: Process of burning a candle; Tearing of paper; Rusting; Curdling of milk; Ripening of fruits; Melting of ice; Folding of clothes; Burning of magnesium; Mixing baking soda with vinegar.
10. 10.
    The experiments shown in Fig. 5.11a, b, c, and d were performed. Find out in which case(s) did lime water turn milky and why?

    • (a) Vinegar and baking soda → gas passed into lime water.
    • (b) Lemon juice and vinegar → gas passed into lime water.
    • (c) Vinegar and common salt → gas passed into lime water.
    • (d) Lemon juice and baking soda → gas passed into lime water.