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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.
- What could be solid X? Write its chemical formula.
- What could be product Y? Write its chemical formula.
- What is the common name of the solution of Y which is used for testing carbon dioxide gas?
- Write chemical equation of the reaction which takes place on adding water to solid X.
- Which characteristic of chemical reactions is illustrated by this example?
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Solution
- Solid X is calcium oxide, commonly known as quicklime. Its chemical formula is CaO.
- Product Y is calcium hydroxide, commonly known as slaked lime. Its chemical formula is Ca(OH)2.
- The common name of the solution of Y is “lime water”, which is used to test carbon dioxide gas.
- \[\ce{CaO_{(s)} + H2O_{(l)} -> Ca(OH)2_{(aq)} + HEAT}\]
- This chemical reaction is characterised by a temperature change because a large amount of heat is evolved, causing the mixture’s temperature to rise.
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