The incident of Tom Sawyer whitewashing a fence as punishment is a famous image in American literature. White wash is a paint made from slaked lime and it becomes shiny after its application on walls due to a reaction with carbon dioxide. This type of reaction is called carbonation.
a) Write the formulae of the substance called slaked lime. 1 b) Write a chemical equation for its preparation. 1
c) Classify the above reaction 1
d) What causes the shine of whitewashed walls due to
Answers
Answer:
(a)Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca(OH)2. It is a colorless crystal or white powder and is obtained when calcium oxide (called lime or quicklime) is mixed, or slaked with water.
(b)The formation of slaked lime (calcium hydroxide, Ca(OH)2) when water is added to lime (CaO) is exothermic. CaO(s) + H2O (l) → Ca(OH)2(s) This reaction occurs when water is added to dry portland cement to make concrete, and heat evolution of energy as heat is evident because the mixture becomes warm.
(c)Calcium oxide reacts vigorously with water to produce slaked lime. This reaction is called 'slaking of lime'. This reaction is a highly exothermic reaction.
(d)In whitewash Calcium hydroxide is present. Calcium hydroxide reacts slowly with the carbon dioxide in air to form a thin layer of calcium carbonate on the walls. Calcium carbonate is formed after two to three days of white washing and gives a shiny finish to the walls.
Explanation:
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