Types of Combination, Materials Required, Theory, Procedure, Observation (For CBSE, ICSE, IAS, NET, NRA 2022)

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Materials Required

  • Quick lime (Calcium oxide)
  • Borosil beaker
  • Glass rod
  • Distilled water
  • Dropper
  • Test tube
  • Litmus paper strips


When calcium oxide is mixed in water it dissolves and forms calcium hydroxide (basic in nature) . During this reaction, a lot of heat is liberated and therefore it is called an exothermic reaction. The equation is as follows:

Due to the basic nature of calcium hydroxide, it turns red litmus paper blue in colour. When carbon dioxide gas is passed through the calcium hydroxide the solution turns milky white.

In the reaction (1) slaked lime is formed by combining two products viz, quick lime and water. Therefore, when two or more than two substances combine to give a single product, it is termed as combining reaction. The reactions accompanied by the evolution of heat are called exothermic reactions.


  • Wash a Borosil beaker with distilled water and dry it.
  • Take a small amount of calcium oxide (quick lime) and slowly add water to it.
  • Wash and take a clean glass rod to stir the mixture of quick lime and water.
  • Touch the beaker carefully from outside.
  • Observe the change.
  • With the help of dropper take a few drops of the mixture from the beaker and place it on red and blue litmus paper strips.
  • Wait and observe.


Mixture in beakerA hissing sound is heard during the reaction when water is added to the beaker containing quick lime. Due to the evolution of heat during the reaction the temperature increases and makes the solution hot.
Solution on litmus paperDrops on the red litmus paper strip change the colour of the paper to blue whereas there is no colour change observed on the blue litmus paper.

Result and Conclusion

From the above experiment we can conclude that the reaction occurred between calcium oxide (Quick lime) and water combine to produce one single product slaked lime is called combination reaction as well as an exothermic reaction.

Precautions to be Taken During the Experiment

  • Take a small amount of compound such as quick lime to perform the experiment.
  • Since the reaction is exothermic avoid touching the mixture directly.
  • Carefully pour water to the Borosil beaker containing calcium oxide (quick lime) .
  • Calcium oxide causes severe burns and therefore it should be handled with a spatula.
  • Use good quality glass beaker during the experiment because if the beaker is of poor quality, then there are chances of crack on the beaker due to the exothermic reaction.


Quick Lime is Also Known as ________

Ans: Calcium oxide (CaO) .

What Type of Reaction Takes Place between Quicklime and Water?

Ans: Combination reaction.

What is the Name of the Product That is Obtained After the Combination Reaction?

Ans: Slaked lime

Combination Reaction That Takes Place between Quicklime and Water is Also Known as ________

Ans: Exothermic reaction.

How to Prepare Lime Water?

Ans: It is a mixture of calcium oxide and water.

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