NCERT Solutions for Class 10 Science Chapter 1 Activity 1.3
Understanding the Activity 🧐
Activity 1.3 from NCERT Solutions for Class 10 Science Chapter 1 explores chemical reactions through a hands-on experiment involving zinc metal and dilute acids. This activity demonstrates two fundamental concepts in chemistry: displacement reactions and exothermic reactions. When a more reactive metal like zinc comes in contact with an acid, it displaces hydrogen from the acid, forming a salt and releasing hydrogen gas. The reaction also releases heat energy, making it an exothermic process. Understanding these concepts is crucial as they form the foundation for studying various chemical processes in nature and industry.
Activity 1.3: Reaction Between Zinc and Dilute Acids
Activity Instructions:
- Take a few zinc granules in a conical flask or a test tube.
- Add dilute hydrochloric acid (&&\ce{HCl}&&) or sulphuric acid (&&\ce{H2SO4}&&) to this.
- CAUTION: Handle the acid with care.
- Observe what happens around the zinc granules.
- Touch the conical flask or test tube and note any change in temperature.
Objective of the Activity 🎯
The primary objective of Activity 1.3 is to observe and analyze the chemical reaction between zinc granules and dilute acids (hydrochloric acid or sulfuric acid). Through this activity, students will witness the formation of hydrogen gas, experience temperature changes, and understand the concepts of displacement and exothermic reactions practically.
Materials Required 🧪
- Zinc granules (&&\ce{Zn}&&) – A few pieces
- Conical flask or test tube – To contain the reaction
- Dilute hydrochloric acid (&&\ce{HCl}&&) or dilute sulphuric acid (&&\ce{H2SO4}&&)
- Safety goggles and gloves – For protection
Procedure: Step-by-Step Guide 📝
Step 1: Place a few zinc granules (&&\ce{Zn}&&) into a clean conical flask or test tube. Make sure the apparatus is clean and dry before starting the experiment.
Step 2: Carefully add dilute hydrochloric acid (&&\ce{HCl}&&) or dilute sulphuric acid (&&\ce{H2SO4}&&) to the container containing the zinc granules. Remember to handle acids with extreme care as they are corrosive!
Step 3: Observe the changes occurring around the zinc granules immediately after adding the acid. Pay close attention to any visible changes such as bubble formation or color changes.
Step 4: Carefully touch the outer surface of the conical flask or test tube (not the mouth where fumes may escape) to check for any changes in temperature. Note whether the container feels warmer or cooler than before.
Observations and Analysis 🔬
What do you observe?
Observation 1: Bubbles are formed around the zinc granules. These bubbles appear vigorously, creating what is called brisk effervescence. The bubbling indicates that a gas is being produced during the reaction. This gas is hydrogen gas (&&\ce{H2}&&), which is released when zinc reacts with the dilute acid.
Observation 2: The conical flask or test tube becomes hot. When you touch the container, you will notice that its temperature has increased significantly. This warming effect indicates that heat energy is being released during the chemical reaction, making it an exothermic reaction.
Chemical Reactions Involved ⚗️
Two types of reactions can occur in Activity 1.3 depending on which acid is used. Let’s examine both:
Reaction 1: Zinc + Dilute Hydrochloric Acid
When zinc (&&\ce{Zn}&&) reacts with dilute hydrochloric acid (&&\ce{HCl}&&), the following displacement reaction occurs:
&&\ce{Zn (s) + 2HCl (aq) -> ZnCl2 (aq) + H2 (g) ^}&&
Word Equation:
Zinc + Hydrochloric Acid → Zinc Chloride + Hydrogen Gas
In this reaction, zinc displaces hydrogen from hydrochloric acid to form zinc chloride (&&\ce{ZnCl2}&&) and hydrogen gas (&&\ce{H2}&&) is released.
Reaction 2: Zinc + Dilute Sulphuric Acid
When zinc (&&\ce{Zn}&&) reacts with dilute sulphuric acid (&&\ce{H2SO4}&&), the following reaction takes place:
&&\ce{Zn (s) + H2SO4 (aq) -> ZnSO4 (aq) + H2 (g) ^}&&
Word Equation:
Zinc + Sulphuric Acid → Zinc Sulphate + Hydrogen Gas
Here, zinc displaces hydrogen from sulphuric acid to form zinc sulphate (&&\ce{ZnSO4}&&) and hydrogen gas (&&\ce{H2}&&) is evolved.
Detailed Explanation 🧠
Why Does This Reaction Occur?
This reaction occurs because zinc is more reactive than hydrogen in the reactivity series of metals. The reactivity series is a list of metals arranged in order of their decreasing reactivity. Metals that are higher in the reactivity series can displace metals (or hydrogen) that are lower in the series from their compounds.
Since zinc (&&\ce{Zn}&&) is more reactive than hydrogen (&&\ce{H}&&), it has the ability to displace hydrogen from acids like &&\ce{HCl}&& or &&\ce{H2SO4}&&. This type of reaction is called a displacement reaction or single displacement reaction.
Understanding Displacement Reactions
A displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound. The general form of a displacement reaction is:
&&\ce{A + BC -> AC + B}&&
In our activity, zinc (&&\ce{Zn}&&) is element A, hydrogen (&&\ce{H}&&) is element B, and the acid (&&\ce{HCl}&& or &&\ce{H2SO4}&&) is compound BC. Zinc displaces hydrogen to form a new compound (zinc chloride or zinc sulphate) and releases hydrogen gas.
Why Is This an Exothermic Reaction?
The reaction between zinc and dilute acids is an exothermic reaction because heat energy is released during the process. In an exothermic reaction, the energy required to break the bonds in the reactants is less than the energy released when new bonds are formed in the products. This excess energy is released to the surroundings in the form of heat, causing the temperature of the reaction vessel to increase.
The general characteristic of exothermic reactions is:
Reactants → Products + Energy (Heat)
Testing for Hydrogen Gas
The hydrogen gas (&&\ce{H2}&&) produced in this reaction can be tested using the burning splint test. When a burning matchstick or splint is brought near the mouth of the test tube, the hydrogen gas burns with a characteristic “pop” sound. This pop sound confirms the presence of hydrogen gas and is a classic test used in chemistry laboratories.
Conclusion and Key Principles ✅
Activity 1.3 from NCERT Solutions for Class 10 Science successfully demonstrates two important types of chemical reactions: displacement reactions and exothermic reactions. Through direct observation, students learn that when zinc (a more reactive metal) reacts with dilute acids, it displaces hydrogen from the acid, forming a salt (zinc chloride or zinc sulphate) and releasing hydrogen gas. The release of heat during the reaction confirms that it is exothermic in nature.
This activity provides a practical understanding of the reactivity series of metals and helps students visualize how chemical reactions involve the breaking and forming of bonds, often accompanied by energy changes. These concepts are fundamental to understanding more complex chemical processes in both nature and industrial applications.
Points to Remember 📌
- Displacement Reaction: A chemical reaction in which a more reactive element displaces a less reactive element from its compound. General form: &&\ce{A + BC -> AC + B}&&
- Reactivity Series: Zinc (&&\ce{Zn}&&) is more reactive than hydrogen (&&\ce{H}&&), so it can displace hydrogen from acids.
- Exothermic Reaction: A reaction that releases heat energy to the surroundings. The temperature of the reaction vessel increases during the reaction.
- Chemical Equations:
&&\ce{Zn + 2HCl -> ZnCl2 + H2}&&
&&\ce{Zn + H2SO4 -> ZnSO4 + H2}&& - Test for Hydrogen Gas: Hydrogen gas burns with a characteristic “pop” sound when a burning splint is brought near it.
- Observable Changes: Formation of bubbles (hydrogen gas) and increase in temperature (heat release) indicate that a chemical reaction is occurring.
- Safety Precautions: Always handle acids with care, wear safety goggles and gloves, and perform the activity under teacher supervision.
- State Symbols: (s) = solid, (aq) = aqueous solution, (g) = gas, (l) = liquid. The upward arrow (↑) indicates gas evolution.
Frequently Asked Questions (FAQ) ❓
What gas is evolved when zinc reacts with dilute hydrochloric acid?
When zinc (&&\ce{Zn}&&) reacts with dilute hydrochloric acid (&&\ce{HCl}&&), hydrogen gas (&&\ce{H2}&&) is evolved. This can be observed as bubbles forming vigorously around the zinc granules during the reaction. The chemical equation is: &&\ce{Zn + 2HCl -> ZnCl2 + H2}&&. The hydrogen gas can be tested by bringing a burning splint near it, which produces a characteristic “pop” sound.
Why does the conical flask become hot during Activity 1.3?
The conical flask becomes hot because the reaction between zinc and dilute acid is an exothermic reaction. In exothermic reactions, chemical energy is converted into heat energy, which is released to the surroundings. The energy released when new bonds form in the products (&&\ce{ZnCl2}&& or &&\ce{ZnSO4}&& and &&\ce{H2}&&) is greater than the energy required to break the bonds in the reactants (&&\ce{Zn}&& and &&\ce{HCl}&&/&&\ce{H2SO4}&&). This excess energy is released as heat, causing the temperature of the flask to increase.
What is the chemical equation for the reaction between zinc and dilute sulfuric acid?
The chemical equation for the reaction between zinc and dilute sulfuric acid is:
&&\ce{Zn (s) + H2SO4 (aq) -> ZnSO4 (aq) + H2 (g) ^}&&
In word form: Zinc + Sulfuric Acid → Zinc Sulfate + Hydrogen Gas
In this reaction, zinc displaces hydrogen from sulfuric acid to form zinc sulfate (&&\ce{ZnSO4}&&), an aqueous salt, and hydrogen gas (&&\ce{H2}&&) is released, which can be observed as bubbles.
What type of chemical reaction occurs in Activity 1.3?
Activity 1.3 demonstrates two types of reactions:
1. Displacement Reaction (Single Displacement Reaction): Zinc, being more reactive than hydrogen, displaces hydrogen from the acid. The general form is &&\ce{A + BC -> AC + B}&&.
2. Exothermic Reaction: The reaction releases heat energy to the surroundings, as evidenced by the warming of the conical flask.
Therefore, the reaction is both a displacement reaction and an exothermic reaction. This demonstrates that a single chemical reaction can be classified into multiple categories based on different characteristics.
Why must acids be handled with care during this activity?
Acids must be handled with care because they are corrosive substances that can cause serious harm. Dilute hydrochloric acid (&&\ce{HCl}&&) and sulfuric acid (&&\ce{H2SO4}&&) can cause:
• Skin burns and irritation on contact
• Eye damage that may lead to permanent vision loss
• Respiratory irritation if fumes are inhaled
• Damage to clothing and other materials
Safety measures include wearing safety goggles and gloves, working in a well-ventilated area, handling acids under teacher supervision, and knowing how to neutralize acid spills using sodium bicarbonate (baking soda) solution.
What is the difference between the reaction of zinc with HCl and H₂SO₄?
Both reactions are very similar in nature, but they produce different salts:
With HCl: &&\ce{Zn + 2HCl -> ZnCl2 + H2}&&
Product: Zinc chloride (&&\ce{ZnCl2}&&)
With H₂SO₄: &&\ce{Zn + H2SO4 -> ZnSO4 + H2}&&
Product: Zinc sulfate (&&\ce{ZnSO4}&&)
Similarities: Both are displacement reactions, both are exothermic (release heat), both produce hydrogen gas (&&\ce{H2}&&), and both show similar observable effects (bubbling and temperature increase).
Difference: The salt formed depends on the acid used—zinc chloride with HCl and zinc sulfate with H₂SO₄.
How can you test for the presence of hydrogen gas in this activity?
Hydrogen gas can be tested using the burning splint test (also called the pop test):
Procedure:
1. Collect the gas evolved during the reaction in a test tube by holding an inverted test tube over the reaction vessel.
2. Once the test tube is filled with the gas, bring a burning matchstick or splint near the mouth of the test tube.
3. Observation: If hydrogen gas is present, it will burn with a characteristic “pop” sound or squeaky pop.
This pop sound is caused by the rapid combustion of hydrogen gas with oxygen in the air: &&\ce{2H2 + O2 -> 2H2O}&&. This is a highly specific and reliable test for hydrogen gas in chemistry laboratories.
Is Activity 1.3 a physical or chemical change?
Activity 1.3 demonstrates a chemical change (or chemical reaction). Here’s why:
Evidence of Chemical Change:
• New substances are formed: Zinc chloride or zinc sulfate and hydrogen gas are produced, which have different properties from the original reactants.
• Energy change: Heat is released (exothermic reaction), indicating chemical bonds are being broken and formed.
• Irreversible: You cannot easily reverse the reaction to get back pure zinc and acid.
• Change in composition: The chemical composition of the reactants has changed—zinc atoms have combined with chloride or sulfate ions, and hydrogen has been released as a gas.
In contrast, a physical change would only involve changes in physical state or appearance without forming new substances (like melting ice or dissolving sugar in water).
Further Reading 📚
For more information and additional activities from NCERT Solutions for Class 10 Science, you can visit the official NCERT website:
NCERT Official Website – https://ncert.nic.in/
The NCERT website provides free access to all textbooks, supplementary materials, and resources for students following the CBSE curriculum.
