Activity 1.4 Class 10 Science

 

Aim of the activity

To observe the reaction between calcium oxide (quick lime) and water to study the change in temperature

Materials Required

   1. Calcium oxide 

   2. Water

   3. Beaker

   4. Stirring rod

Procedure

We will take a small amount of calcium oxide(quick lime) in a beaker and slowly add water in it and stirring the mixture gently.

Observation

   1.  When water is added to calcium oxide, a vigorous reaction takes place.

   2. A hissing sound is produced and a bubble can be seen.

   3. The beaker becomes very hot which indicates the rise in the temperature.

   4.  A white solution is of slaked lime (calcium hydroxide)

Explanation

The reaction between calcium oxide and water is highly exothermic.

Calcium hydroxide is formed and heat is released during the reaction.

Chemical reaction of Calcium oxide and water

CaO + H2O →Ca(OH)2 + heat

The reaction is a combination reaction.

The heat released during the reaction is responsible for the increase in the temperature of the beaker.

Calcium hydroxide is slightly soluble in water and forms a suspension called lime water.

Conclusion

Through this activity, we can conclude that the reaction between calcium oxide and water is vigorous and the reaction is exothermic reaction.

Frequently Asked Questions

   1. What type of reaction occurs between calcium oxide and water?

Ans – In this reaction, both calcium oxide and water combine to form a new single product calcium hydroxide, so it is a combination reaction.

   2. Why does the temperature of the beaker increase?

Ans – Heat is released during the reaction so the temperature of the beaker increases.

   3. What is the chemical formula of quick lime?

Ans - CaO

   4. What is slaked lime used for?

Ans – Slaked lime (Ca(OH)2) is used in whitewashing the wall of houses.

   5. What happens if more water is added to the mixture during the reaction?

Ans – If more water is added, slaked lime dissolves forming a clear solution called lime water.

   6. Why should water be added slowly to calcium oxide?

Ans – Water should be added slowly to prevent the reaction from becoming too vigorous and to reduce the risk of splashing caused by the release of heat.

   7. What is the chemical name of slaked lime?

Ans – Calcium hydroxide

 

Important extra points

   1. Slaked lime is used in whitewashing.

   2. Lime is used in manufacturing glass and cement.

   3. Lime water turns milky when carbon dioxide is passed through it.

Safety Precautions: -

   1. Slaked lime solution can cause severe burns on contact with the eye and skin so always wear gloves and goggles during the activity.

   2. Water should be added slowly to prevent the splashing.

   3. Activity must be done in a well-ventilated area.

You can also explore

   1. After performing this activity, you can pass carbon dioxide to the lime water and observe how it turns milky.

   2. Test the alkalinity  of lime water after filtering the solution with litmus paper

Fun facts

Calcium oxide is commonly known as quick lime and is known as slaked lime when water is added to it.

Multiple Choice Questions

   1. What is the chemical formula of quick lime?

   a.  Ca(OH)2

   b. CaO

   c.  CaCO3

   d. CaCl2

Correct answer-  (b) CaO

   2. What happens when water is added to calcium oxide?

   a.  It cools down

   b . Temperature increases

   c.  No change

   d . A gas is released

Correct answer – (b)

   3. What is the product formed during this activity?

   a.  Calcium hydroxide

   b. Calcium oxide

   c.  Calcium carbonate

   d. Calcium chloride

Correct answer –(a)

   4. What type of chemical reaction takes place in this activity?

   a.  Displacement reaction

   b. Decomposition reaction

   c.  Combination reaction

   d. Neutralization reaction

Correct answer –(c)

   5. What is the product's common name formed during this activity?

   a.  Quick lime

   b. Lime water

   c.  Slaked lime

   d. Bleaching powder

Correct answer –(c)

   6. What is the reaction between CaO and H2O is an example of?

   a.  Endothermic reaction

   b. Exothermic reaction

   c.  Oxidation reaction

   d. Reduction reaction

Correct answer –(b)

   7. What is the nature of calcium hydroxide? 

   a.  Acidic

   b. Neutral

   c.  Basic

   d. Amphoteric

Correct answer –(c)

   8. What happens when carbon dioxide is passed through lime water?

   a.  Lime turns milky

   b. Lime water remains clear

   c.  Lime water turns yellow

   d. No change

Correct answer –(a)