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. (True/False) (ii) Collecting water vapour by condensing involves a chemical change. (True/False) (iii) The process of converting leaves into compost is a chemical change. (True/False) (iv) Mixing baking soda with lemon juice is a chemical change. (True/False)
True. The wax melts, travels up the wick, vaporizes, and then burns to produce a flame.
False. Collecting water vapour by condensing involves a physical change. Condensation is the process of changing water vapour (gas) to liquid water without forming any new substance.
True. Decomposition of leaves by bacteria and fungi produces compost, which is a new substance formed through chemical reactions.
True. Mixing baking soda with lemon juice produces carbon dioxide gas and other substances, indicating a chemical change.
Explanation
(i) The chapter explains in Activity 5.7 that the wax of the candle melts, is carried up the wick, and evaporates due to the heat of the flame. The vapour of wax then burns to produce a flame. (ii) The chapter states that when water evaporates, it can be condensed back into liquid water. This is a reversible physical change where no new substance is formed. (iii) The chapter mentions that decomposition of food waste into compost is a chemical change where new substances are formed. (iv) Activity 5.4 in the chapter demonstrates that mixing vinegar (similar to lemon juice) with baking soda produces carbon dioxide gas, which turns lime water milky. This formation of a new substance confirms it is a chemical change.