Review
Question: Which product is formed when calcium oxide reacts with water?
Correct Answer
Slaked lime
ExplanationOn reaction of calcium oxide with water, it gives calcium hydroxide and heat.
CaO(s) + H2O → Ca(OH)2 + Heat
The general name of calcium oxide (CaO) is quick lime and the general name of calcium hydroxide (Ca(OH)2) is slaked lime.
Since, in the reaction calcium oxide and water combined together, hence this is an example of Combination Reaction. And as heat is evolved in this reaction, thus this is an Exothermic Reaction also.
Calcium hydroxide formed in this reaction is used to paint the walls of houses especially outer walls. The painting of walls, trees, etc. is known as Whitewashing, Calcimine, Kalsomine or lime paint.
The painting using calcium hydroxide, in two to three days reacts with carbon dioxide present in air and forms calcium carbonate in the form of calcite. Formation of Calcium carbonate makes paint hard and gives a shiny look to walls. Lime wash produces unique surface glow due to the double refraction of calcite crystals.
This reaction is known as carbonation or carbonatation.
Lime wash has antibacterial property also. Because of this walls of dairy, masonary, lower trunk of trees, etc. are whitewashed. Along with antibacterial properties, trees along the road sides, whose lower trunk is painted with white colour, reflect light in the night and makes the night driving more safe.
In Britain and Ireland, whitewash was used in ancient times in the cottage of workers. And whitewashing is still retains something with rural poverty. It was prevalent in United States also. As it was so called associated with rural poverty, hence there is an old saying "Too proud to whitewash and too poor to paint".