This activity1.4 helps students understand the reaction between calcium oxide and water. When
water is added to calcium oxide, a vigorous chemical reaction takes place. This
activity demonstrates both combination reaction and exothermic reaction.
Activity 1.4 Class 10 Science
Objective
To observe and demonstrate the chemical reaction between calcium oxide with water.
Materials Required
1. Calcium oxide (Quick lime)
2. Water
3. Beaker
Procedure
· Take a small amount of calcium oxide in a beaker.
· Slowly add water to the beaker.
· Observe the reaction carefully.
· Touch the outer surface of the beaker carefully and note any change in the temperature.
Observation
· A vigorous reaction takes place.
· The beaker becomes hot due to the release of heat.
· A hissing sound is heard during the reaction. Bubbles may be observed.
· After cooling a white suspension of calcium hydroxide (slaked lime) is formed.
Chemical reaction involved in the activity
CaO(s) + H2O(I) → Ca(OH)2(aq)
Explanation
When water is added to calcium oxide, a vigorous reaction takes place and calcium hydroxide
is formed and a large amount of heat is released, that’s why beaker becomes
hot.
Since heat is released during the reaction, it is called an exothermic reaction.
In this activity, two reactants combine to form a single product so it is called a
combination reaction.
Types of Chemical Reactions
1. Combination reaction: A reaction in which two or more substances combine to form a single
product is called a combination reaction.
2. Exothermic reaction: A reaction in which heat is released is called an exothermic
reaction.
Conclusion
The activity 1.4 demonstrates the vigorous reaction between calcium oxide and
water. This is an exothermic reaction. As CaO combine with water to form Ca (OH)2 only so this is a combination reaction.
Precautions
· Add waterslowly to calcium oxide.
· Performthe activity under the supervision of a teacher.
· Avoid directcontact with calcium oxide and the reaction mixture.
· Use cleanapparatus.
· Do nottouch the reaction mixture directly as it becomes hot.
VivaQuestions and Answers
Q1. Whatis the common name of calcium oxide?
Answer
Quick lime
Q2. What is the common name of calcium hydroxide?
Answer
Slaked lime
Q3. What happens when water is added to calcium oxide?
Answer
A vigorous
reaction takes place and calcium hydroxide is formed.
Q4. Why does the beaker become hot?
Answer
Because heat is released during the reaction so the beaker becomes hot.
Q5. Which type of rection is demonstrated in this activity.?
Answer
Combination
reaction and exothermic reaction
Q6. What is the chemical formula of calcium hydroxide?
Answer
Ca(OH)2
Q7. Why is this called a combination reaction?
Answer
Because calcium oxide and water combine to form a single product.
Key Learning Points
· Calcium oxide reacts with water to form calcium hydroxide.
· A large amount of heat is released during the reaction.
· The reaction is vigorous in nature.
· Calcium hydroxide is known as slaked lime.
· The reaction is both combination and exothermic.
Multiple Choice Question
Q1. What is the common name of calcium oxide?
a. Slaked lime
b. Quick lime
c. Limestone
d. Gypsum
Correct answer – b. Quick lime
Q2. What is formed when calcium oxide reacts with water?
a. Calcium
carbonate
b. Calcium
chloride
c. Calcium
hydroxide
d. Calcium
sulphate
Correct answer – c. Calcium hydroxide
Q3. What is the common name of calcium hydroxide?
a. Quick lime
b. Slaked lime
c. Lime water
d. Chalk
Correct answer – b. Slaked lime
Q4. Why does the beaker become hot during the reaction?
a. Heat is
absorbed
b. Heat is
released
c. Water evaporates
d. Oxygen is produced
Correct answer – b. Heat is released
Q5. Which type of reaction is represented by CaO(s) + H2O(I) → Ca(OH)2(aq)
a.Decomposition reaction
b.Double displacement reaction
c.Displacement reaction
d.Combination reaction
Correctanswer – d. Combination reaction
Q6.This reaction CaO(s) + H2O(I)→ Ca(OH)2(aq) is also classified as:
a.Endothermic reaction
b.Exothermic reaction
c.Neutralization reaction
d.Oxidation reaction
Correctanswer – b. Exothermicreaction
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