NCERT Class 10 Science | Chapter 1(Chemical Reactions and Equations) Activities | RMVS Class Tuitions

 

Chapter 1: Chemical Reactions and Equations

Activity 1.1

What is Activity 1.1 about?

This activity shows that burning magnesium is a chemical reaction and helps us understand:

• What happens during a chemical reaction

• Formation of a new substance

• Need for balancing a chemical equation

Aim of the Activity

To observe a chemical reaction by burning magnesium ribbon in air.

Materials Required

• Magnesium ribbon

• Burner / spirit lamp

• Tongs

Procedure (Write in simple steps)

1. Take a clean magnesium ribbon.

2. Hold it with tongs.

3. Burn it over a flame.

4. Observe the changes carefully.

(Cleaning the ribbon is important to remove the oxide layer.)

Observation (VERY IMPORTANT)

• Magnesium ribbon burns with a dazzling white flame.

• A white powder is formed after burning.

Chemical Reaction Involved

2Mg(s) + O₂(g) → 2MgO(s)

Product Formed

Magnesium oxide (MgO)

It is a new substance with properties different from magnesium.

Conclusion (Write this in exams)

Burning of magnesium ribbon in air is a chemical reaction because:

• A new substance (magnesium oxide) is formed

• Heat and light energy are released

• The reaction is irreversible

Important Concept Behind the Activity

This activity proves:

• Law of conservation of mass

• Chemical reactions involve rearrangement of atoms

• Reactants → Products

Exam-Focused Questions from Activity 1.1

Q1. Why is magnesium ribbon cleaned before burning?

Answer:
To remove the layer of magnesium oxide so that magnesium burns easily in air.

Q2. Name the type of reaction involved.

Answer:
Combination reaction (Magnesium combines with oxygen)

Q3. Why is this reaction called a chemical change?

Answer:
Because a new substance with different properties is formed.

Q4. What kind of flame is observed?

Answer:
A bright white dazzling flame.

One-Line Revision (Must Remember)

• Burning magnesium = Combination reaction

• Product = Magnesium oxide

• Energy released = Heat + Light

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Activity 1.2

Aim of the Activity

To observe a chemical reaction when lead nitrate solution is mixed with potassium iodide solution.

Materials Required

• Lead nitrate solution

• Potassium iodide solution

• Test tube / beaker

Procedure (Write stepwise)

1. Take lead nitrate solution in a test tube.

2. Add potassium iodide solution to it.

3. Shake the test tube gently.

4. Observe the change.

Observation (VERY IMPORTANT)

• A bright yellow precipitate is formed immediately.

Chemical Reaction Involved

Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s)↓ + 2KNO₃(aq)

Product Formed

• Lead iodide (PbI₂) → Yellow precipitate

• Potassium nitrate (KNO₃) → Remains in solution

Type of Reaction

Double Displacement Reaction

(Because exchange of ions takes place.)

Why is it called a Precipitation Reaction?

Because an insoluble solid (PbI₂) is formed from two aqueous solutions.

Conclusion (Board Language)

The reaction between lead nitrate and potassium iodide is a chemical reaction as:

• A new substance is formed

• A precipitate appears

• The reaction is irreversible

Exam-Focused Questions from Activity 1.2

Q1. What is the colour of the precipitate formed?

Answer: Yellow

Q2. Name the precipitate formed.

Answer: Lead iodide (PbI₂)

Q3. Why is this reaction called double displacement?

Answer:
Because there is an exchange of ions between lead nitrate and potassium iodide.

Q4. State one reason why this is a chemical reaction.

Answer:
Formation of a new insoluble substance (precipitate).

Key Words Examiners Look For

• Yellow precipitate

• Double displacement reaction

• Precipitation reaction

• PbI₂

One-Line Revision

Lead nitrate + Potassium iodide → Yellow PbI₂ precipitate

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Activity 1.3

Aim of the Activity

To study the reaction between zinc granules and dilute hydrochloric acid and identify the gas evolved.

Materials Required

• Zinc granules

• Dilute hydrochloric acid (HCl)

• Conical flask

• Cork

• Delivery tube

• Test tube

• Burning matchstick

Procedure (Write neatly in exams)

1. Take a few zinc granules in a conical flask.

2. Add dilute hydrochloric acid to it.

3. Fit the flask with a cork having a delivery tube.

4. Collect the gas evolved in a test tube.

5. Bring a burning matchstick near the mouth of the test tube.

Observation (VERY IMPORTANT)

• Effervescence is observed.

• A colourless gas has evolved.

• The gas burns with a ‘pop’ sound.

Chemical Reaction Involved

Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)↑

Gas Identified

Hydrogen gas (H₂)

Test for Hydrogen Gas

When a burning matchstick is brought near hydrogen gas, it burns with a ‘pop’ sound.

Type of Reaction

Displacement Reaction

Reason:
Zinc, being more reactive, displaces hydrogen from hydrochloric acid.

Why is this a Chemical Reaction?

• New substances are formed (ZnCl₂ and H₂)

• Gas is evolved

• The reaction is irreversible

Exam-Focused Questions from Activity 1.3

Q1. Name the gas evolved in this reaction.

Answer: Hydrogen gas

Q2. How is hydrogen gas tested?

Answer:
By the ‘pop’ test using a burning matchstick.

Q3. Why is zinc able to displace hydrogen?

Answer:
Because zinc is more reactive than hydrogen.

Q4. State the type of reaction.

Answer: Displacement reaction

Important Safety Precaution

• Use dilute acid, not concentrated.

• Handle acids carefully.

One-Line Revision

Zinc + dilute HCl → Hydrogen gas with pop sound

Activity 1.4

Aim of the Activity

To study the reaction between calcium oxide (quick lime) and water.

Materials Required

• Calcium oxide (CaO)

• Water

• Beaker

Procedure (Write in steps)

1. Take a small amount of calcium oxide in a beaker.

2. Slowly add water to it.

3. Touch the beaker carefully and observe.

Observation (VERY IMPORTANT)

• The beaker becomes hot.

• A white slurry is formed.

Chemical Reaction Involved

CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat

Product Formed

Calcium hydroxide (slaked lime)

Nature of Reaction

Exothermic reaction

Reason:
Heat is released during the reaction.

Type of Reaction

Combination reaction

Reason:
Two substances combine to form a single product.

Conclusion (Board Language)

The reaction between calcium oxide and water is a chemical reaction because:

• A new substance is formed

• Heat is released

• The reaction is irreversible

Exam-Based Questions from Activity 1.4

Q1. Why does the beaker become hot?

Answer:
Because the reaction is exothermic and releases heat.

Q2. Name the product formed.

Answer: Calcium hydroxide (slaked lime)

Q3. Write the balanced chemical equation.

Answer:
CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat

Q4. State the type of reaction.

Answer: Combination reaction

One-Line Revision

Quick lime + Water → Slaked lime + Heat

Activity 1.5

Aim of the Activity

To study the effect of heat on ferrous sulphate crystals.

Materials Required

• Ferrous sulphate crystals (FeSO₄·7H₂O)

• Dry boiling tube

• Burner

Procedure (Write stepwise)

1. Take about 2 g of ferrous sulphate crystals in a dry boiling tube.

2. Heat the boiling tube gently.

3. Observe the changes in colour and smell.

Observation (VERY IMPORTANT)

1. Initial colour: Light green crystals

2. On heating:

• Crystals lose water of crystallisation and turn white

• On strong heating, a brown solid is formed

3. A gas with a smell of burning sulphur is evolved.

Chemical Reactions Involved

FeSO₄·7H₂O(s) → FeSO₄(s) + 7H₂O(g)

2FeSO₄(s) → Fe₂O₃(s) + SO₂(g) + SO₃(g)

Gases Evolved

• Sulphur dioxide (SO₂)

• Sulphur trioxide (SO₃)

Type of Reaction

Decomposition reaction

(One compound breaks into simpler substances on heating.)

Nature of Reaction

Endothermic reaction

(Heat is absorbed.)

Why is this a Chemical Reaction?

• New substances are formed

• Colour change is observed

• Gases are evolved

Exam-Focused Questions from Activity 1.5

Q1. What is the colour change observed?

Answer:
Green → White → Brown

Q2. Name the brown residue formed.

Answer: Ferric oxide (Fe₂O₃)

Q3. Identify the gases that evolved.

Answer: Sulphur dioxide and sulphur trioxide

Q4. What type of reaction is this?

Answer: Decomposition reaction

Important Board Tip

If the question says:

“Heating ferrous sulphate crystals…”

Immediately write:

• Green to brown colour change

• SO₂, SO₃ gases

• Decomposition reaction

One-Line Revision

Ferrous sulphate on heating → Ferric oxide + SO₂ + SO₃

Activity 1.6

Aim of the Activity

To study the effect of heat on lead nitrate.

Materials Required

• Lead nitrate powder [Pb(NO₃)₂]

• Boiling tube

• Burner

Procedure (Write in steps)

1. Take about 2 g of lead nitrate powder in a boiling tube.

2. Heat the boiling tube carefully over a flame.

3. Observe the changes.

Observation (VERY IMPORTANT)

• Brown fumes have evolved.

• A yellow residue is left in the boiling tube.

Chemical Reaction Involved

2Pb(NO₃)₂(s) → 2PbO(s) + 4NO₂(g) + O₂(g)

Products Formed

• Lead oxide (PbO) → Yellow solid residue

• Nitrogen dioxide (NO₂) → Brown fumes

• Oxygen (O₂) → Colourless gas

Type of Reaction

Thermal decomposition reaction

Nature of Reaction

Endothermic reaction

(Heat is absorbed.)

Why is it a Chemical Reaction?

• New substances are formed

• Colour change is observed

• Gases are evolved

Exam-Based Questions from Activity 1.6

Q1. What is the colour of fumes evolved?

Answer: Brown

Q2. Name the gas responsible for brown fumes.

Answer: Nitrogen dioxide (NO₂)

Q3. Name the residue left behind.

Answer: Lead oxide (PbO)

Q4. State the type of reaction.

Answer: Decomposition reaction

Safety Precaution (IMPORTANT)

• Perform the experiment in a well-ventilated area

• Do not inhale the brown fumes (NO₂ is toxic)

One-Line Revision

Heating lead nitrate → Yellow PbO + Brown NO₂ fumes + O₂

Teacher’s Board Tip

If you see:

“Brown fumes on heating a salt…”

Immediately think:

• Lead nitrate

• Nitrogen dioxide

• Decomposition reaction

Activity 1.7 – Electrolysis of Water

Aim of the Activity

To show that water decomposes into hydrogen and oxygen gases on passing electric current.

Materials Required

• Plastic mug

• Two carbon electrodes

• 6-volt battery

• Switch

• Connecting wires

• Acidulated water (water + few drops of dilute sulphuric acid)

• Two test tubes

Why a Plastic Mug is Used?

Because plastic is an insulator and does not conduct electricity, making the experiment safe.

Procedure (Write stepwise)

1. Take a plastic mug and fill it with acidulated water.

2. Fix two carbon electrodes in the mug.

3. Connect the electrodes to a 6-volt battery.

4. Invert two test tubes over the electrodes.

5. Switch on the current and observe.

Observation (VERY IMPORTANT)

• Bubbles of gas appear at both electrodes.

• More gas is collected at the cathode.

• Less gas is collected at the anode.

Identification of Gases

• Gas at cathode → Hydrogen (H₂)

• Burns with a pop sound

• Gas at anode → Oxygen (O₂)

• Rekindles a glowing splint

Volume Ratio of Gases

Hydrogen : Oxygen = 2 : 1

Chemical Reaction Involved

2H₂O(l) → 2H₂(g) + O₂(g)

Type of Reaction

Electrolytic decomposition reaction

Conclusion (Board Language)

Water is a compound because it decomposes into hydrogen and oxygen on passing electric current.

Exam-Based Questions from Activity 1.7

Q1. Why is sulphuric acid added to water?

Answer:
To increase the electrical conductivity of water.

Q2. Which gas is collected in larger amounts?

Answer: Hydrogen gas

Q3. Why is the volume of hydrogen double that of oxygen?

Answer:
Because water contains hydrogen and oxygen in the ratio 2 : 1.

One-Line Revision

Electrolysis of water → Hydrogen + Oxygen (2:1)

Activity 1.8

Aim of the Activity

To study the effect of sunlight on silver chloride.

Materials Required

• Silver chloride (AgCl) – about 2 g

• China dish / watch glass

• Sunlight

Procedure (Write stepwise)

1. Take about 2 g of silver chloride in a china dish.

2. Place the dish in sunlight for some time.

3. Observe the change carefully.

Observation (VERY IMPORTANT)

• White silver chloride turns grey in sunlight.

Chemical Reaction Involved

2AgCl(s) → 2Ag(s) + Cl₂(g)
In the presence of sunlight

Reason for Colour Change

Grey colour appears due to the formation of metallic silver.

Type of Reaction

Photochemical decomposition reaction

(Decomposition occurs due to light energy.)

Nature of Reaction

Endothermic reaction

(Energy is absorbed from sunlight.)

Conclusion (Board Language)

Silver chloride undergoes decomposition in the presence of sunlight, proving that light energy can cause chemical reactions.

Importance of This Reaction (Exam Favourite)

This reaction is used in:

• Black and white photography

Exam-Based Questions from Activity 1.8

Q1. Why does silver chloride turn grey in sunlight?

Answer:
Due to the formation of metallic silver.

Q2. Name the gas released in this reaction.

Answer: Chlorine gas

Q3. State the type of reaction.

Answer: Photochemical decomposition reaction

Q4. Why should silver chloride be stored in dark containers?

Answer:
Because it decomposes in the presence of sunlight.

One-Line Revision

Silver chloride + Sunlight → Silver + Chlorine

Teacher’s Board Tip

If the question mentions:

“White salt turning grey in sunlight…”

Immediately think:

• Silver chloride

• Photochemical decomposition

• Photography

Activity 1.9

Aim of the Activity

To show that iron is more reactive than copper.

Materials Required

• 3 clean iron nails

• Copper sulphate solution (blue)

• Test tube / beaker

Procedure (Write stepwise)

1. Take about 10 mL of copper sulphate solution in a test tube.

2. Put three clean iron nails into the solution.

3. Leave it undisturbed for about 20–30 minutes.

4. Observe the changes.

(Iron nails are cleaned to remove rust.)

Observation (VERY IMPORTANT)

• The blue colour of copper sulphate solution fades.

• A reddish-brown coating appears on the iron nails.

Chemical Reaction Involved

Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

Explanation of Observation

• Iron displaces copper from copper sulphate solution.

• Copper is deposited on iron nails.

• Formation of iron sulphate causes the colour change.

Type of Reaction

Displacement reaction

Conclusion (Board Language)

Iron is more reactive than copper; therefore, it displaces copper from its compound.

Exam-Based Questions from Activity 1.9

Q1. Why does the blue colour of solution fade?

Answer:
Due to the formation of iron sulphate.

Q2. What is the reddish-brown deposit?

Answer: Copper

Q3. Why are iron nails cleaned before the experiment?

Answer:
To remove rust so that iron can react properly.

Q4. State the type of reaction.

Answer: Displacement reaction

One-Line Revision

Iron + Copper sulphate → Iron sulphate + Copper

Teacher’s Board Tip

If the question says:

“Blue solution turns green and brown coating appears…”

Immediately think:

• Displacement reaction

• Iron displaces copper

• Balanced equation

Activity 1.10

Aim of the Activity

To observe a double displacement (precipitation) reaction.

Materials Required

• Sodium sulphate solution (about 3 mL)

• Barium chloride solution

• Test tube

Procedure (Write stepwise)

1. Take about 3 mL of sodium sulphate solution in a test tube.

2. Add barium chloride solution to it.

3. Shake the test tube gently.

4. Observe the change.

Observation (VERY IMPORTANT)

• A white precipitate is formed immediately.

Chemical Reaction Involved

Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s)↓ + 2NaCl(aq)

Precipitate Formed

Barium sulphate (BaSO₄) — white in colour

Type of Reaction

Double displacement reaction

Why is it called a Precipitation Reaction?

Because an insoluble solid (BaSO₄) is formed from two aqueous solutions.

Conclusion (Board Language)

This reaction shows that exchange of ions takes place between two compounds resulting in the formation of a precipitate.

Exam-Based Questions from Activity 1.10

Q1. Name the white precipitate formed.

Answer: Barium sulphate

Q2. State the type of reaction.

Answer: Double displacement reaction

Q3. Why is this reaction also called a precipitation reaction?

Answer:
Because an insoluble solid is formed.

One-Line Revision

Sodium sulphate + Barium chloride → White BaSO₄ precipitate

Teacher’s Final Board Tip (Chapter 1)

If a question mentions:

• Two colourless solutions

• White precipitate

Immediately think:

• BaSO₄

• Double displacement reaction

Activity 1.11

Aim of the Activity

To study the oxidation of copper on heating.

Materials Required

• Copper powder (about 1 g)

• China dish

• Burner

Procedure (Write stepwise)

1. Take about 1 g of copper powder in a china dish.

2. Heat the copper powder strongly over a flame.

3. Observe the change in colour.

Observation (VERY IMPORTANT)

• The reddish-brown copper powder turns black on heating.

Chemical Reaction Involved

2Cu(s) + O₂(g) → 2CuO(s)
(Heat)

Product Formed

Copper(II) oxide (CuO) — black in colour

Explanation

Copper reacts with oxygen present in air to form copper oxide.

Type of Reaction

Combination reaction

Nature of Reaction

Oxidation reaction

Reason:
Copper gains oxygen.

Conclusion (Board Language)

Heating copper powder in air results in the oxidation of copper, forming black copper oxide.

Exam-Based Questions from Activity 1.11

Q1. What colour change is observed?

Answer: Reddish-brown to black

Q2. Name the black substance formed.

Answer: Copper(II) oxide

Q3. Why is this reaction called oxidation?

Answer:Because copper gains oxygen.

Q4. State the type of reaction.

Answer: Combination reaction

One-Line Revision

Copper + Oxygen → Black copper oxide

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