Question

When water is added gradually to a white solid X, a hissing sound is heard and a lot of heat is produced forming a product Y. A suspension of Y in water is applied to the walls of a house during white washing. A clear solution of Y is also used for testing carbon dioxide gas in the laboratory.

1. What could be solid X? Write its chemical formula.
2. What could be product Y? Write its chemical formula.
3. What is the common name of the solution of Y which is used for testing carbon dioxide gas?
4. Write chemical equation of the reaction which takes place on adding water to solid X.
5. Which characteristic of chemical reactions is illustrated by this example?

Answer 1

1. Solid X is calcium oxide, commonly known as quicklime. Its chemical formula is CaO.
2. Product Y is calcium hydroxide, commonly known as slaked lime. Its chemical formula is Ca(OH)₂.
3. The common name of the solution of Y is “lime water”, which is used to test carbon dioxide gas.
4. \[\ce{CaO_{(s)} + H2O_{(l)} -> Ca(OH)2_{(aq)} + HEAT}\]
5. This chemical reaction is characterised by a temperature change because a large amount of heat is evolved, causing the mixture’s temperature to rise.