Chapter 4: Changes around us

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Changes around us


A thick coating of a paste of Plaster of Paris (POP) is applied over the bandage on a fractured bone. It becomes hard on drying to keep the fractured bone immobilised. Can the change in POP be reversed?


The chemical name of Plaster of Paris is calcium sulphate hemihydrate. When we add water to it, it becomes hardened due to the formation of a new substance, called gypsum. Here, the chemical composition of Plaster of Paris changes which leads to the formation of gypsum. So, it is a chemical change that cannot be reversed. 

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