Q29 of 44 Page 5

Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?


When the grapes are attached to the plants, they are still considered as living. They have their immune system intact, due to which they cannot undergo fermentation. After the grapes are plucked, microbes are made to attack them, in the absence of air, to form alcohol. This process is called fermentation and it is a chemical process.


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Which among the following are physical or chemical changes?

(a) Evaporation of petrol


(b) Burning of Liquefied Petroleum Gas (LPG)


(c) Heating of an iron rod to red hot.


(d) Curdling of milk


(e) Sublimation of solid ammonium chloride

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During the reaction of some metals with dilute hydrochloric acid, following observations were made.

(a) Silver metal does not show any change


(b) The temperature of the reaction mixture rises when aluminium (Al) is added.


(c) The reaction of sodium metal is found to be highly explosive


(d) Some bubbles of a gas are seen when lead (Pb) is reacted with the acid. Explain these observations giving suitable reasons.