Question
(1) Give an example for each of the following with proper explanation:
a) A physical change which is reversible.
b) A chemical change in which change of colour is observed.
(2) How would you show that setting of curd is a chemical change? [3 MARKS]
a) A physical change which is reversible.
b) A chemical change in which change of colour is observed.
(2) How would you show that setting of curd is a chemical change? [3 MARKS]
Answer:
:
(1) Each part: 1 Mark
(2) Answer: 1 Mark
(1) a) In case of water, when it is cooled up tozero degree Celsius it becomes ice. However, when the ice is left in a warm room, it becomes liquid again. So, the change occurs only in its phase which is a physical change and reversible.
b) Rusting of iron is an example of a chemical change in which colour change is observed. If we leave a piece of iron in open for some time, it acquires a film of brownish substance.This substance is called rust and the process is called rusting.
Iron(Fe)+Oxygen(O2,fromtheair)+water(H2O)→Rust(ironoxide)(Fe2O3.H2O)
(2) After the formation of curd, milk cannot be re-obtained from it. Also, both milk and curd have different properties. Since these are the properties of a chemical change, setting of curd is a chemical change.
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:
(1) Each part: 1 Mark
(2) Answer: 1 Mark
(1) a) In case of water, when it is cooled up tozero degree Celsius it becomes ice. However, when the ice is left in a warm room, it becomes liquid again. So, the change occurs only in its phase which is a physical change and reversible.
b) Rusting of iron is an example of a chemical change in which colour change is observed. If we leave a piece of iron in open for some time, it acquires a film of brownish substance.This substance is called rust and the process is called rusting.
Iron(Fe)+Oxygen(O2,fromtheair)+water(H2O)→Rust(ironoxide)(Fe2O3.H2O)
(2) After the formation of curd, milk cannot be re-obtained from it. Also, both milk and curd have different properties. Since these are the properties of a chemical change, setting of curd is a chemical change.
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