Chemistry - Story Board
Текст Раскадровки
- Arun is returning from the school.
- What is happening over here father?
- Oh Arun! you ae back home. See the walls are being white washed today.
- Wow! that's great. By the way father what exactly white wash is and how it is prepared?
- Now that is a good question! Whitewash, or calcimine, or lime paint is a type of paint made from slaked lime (calcium hydroxide, Ca(OH)₂) which is prepared by adding water(H2O) to Quick lime(CaO).
- Wow! So is this a chemical or physical change?
- Of course it is a chemical change as heat is evolved in the formation of Calcium hydroxide. You can check it by feeling the bucket. it will be warm.
- Hmm., understood. Just one last question. Why do the walls shine after 2-3 days of white wash and why they become wet?
- That's because, after white washing the walls, when carbon dioxide(CO2) comes in contact with calcium hydroxide[Ca(OH)2], it reacts to form a thin layer of Calcium Carbonate(CaCO3) on the walls which is also called lime stone or marble along with water. The shine is due to CaCO3 and the wetness is due to the water released. And both, forming of calcium hydroxide and calcium carbonate, is a type of combination reaction as two or more substances/reactants chemically combine together to form a single product with release of energy.
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