Class 9 Science Notes Chapter 3 (Chapter 3) – Lab Manual (English) Book

Alright class, let's focus on Chapter 3 from your Science Lab Manual. This chapter is crucial as it deals with identifying and differentiating between physical and chemical changes through a series of experiments. Understanding these concepts is fundamental for chemistry and frequently tested in various government exams.

Chapter 3: Physical and Chemical Changes

Aim: To perform specific reactions and classify them as either physical or chemical changes based on observations.

Core Concepts:

1. Physical Change:

   • A change in which only the physical properties (like state, shape, size, colour, texture) of a substance change.
   • No new substance is formed.
   • The chemical composition of the substance remains the same.
   • These changes are generally reversible.
   • Examples: Melting of ice, boiling of water, dissolving sugar in water, cutting paper, bending a wire.

2. Chemical Change:

   • A change in which one or more new substances with entirely different chemical compositions and properties are formed.
   • The original substance(s) lose their identity.
   • These changes are generally irreversible by simple physical means.
   • Often accompanied by observable indicators like:
     • Change in Colour: e.g., Iron rusting (silvery grey to reddish-brown).
     • Evolution of a Gas: e.g., Reaction of acid with metal.
     • Formation of a Precipitate: An insoluble solid formed when two solutions are mixed.
     • Production of Heat, Light, or Sound: e.g., Burning of fuel.
     • Change in Smell: e.g., Rotting of food.
   • Examples: Burning of wood, rusting of iron, digestion of food, cooking of egg, reaction between vinegar and baking soda.

Experiments and Observations:

Experiment 3(a): Reaction between Iron (Fe) and Copper Sulphate (CuSO₄) solution

• Materials: Iron nails (cleaned), Copper Sulphate solution (blue), test tube, thread, sandpaper.
• Procedure:
  1. Clean iron nails with sandpaper.
  2. Take blue Copper Sulphate solution in a test tube.
  3. Immerse one or two iron nails tied with a thread into the solution. Keep one nail aside for comparison.
  4. Observe the changes after about 15-20 minutes.
• Observations:
  1. The blue colour of the Copper Sulphate solution gradually fades and turns light green.
  2. A reddish-brown coating deposits on the surface of the iron nails immersed in the solution.
• Chemical Equation: Fe (s) + CuSO₄ (aq) (Blue) → FeSO₄ (aq) (Light Green) + Cu (s) (Reddish-brown)
• Conclusion: This is a Chemical Change because:
  • New substances (Iron Sulphate and Copper) are formed.
  • There is a distinct colour change in the solution and deposition on the nail.
  • It's a displacement reaction where more reactive iron displaces copper from its salt solution.

Experiment 3(b): Burning of Magnesium (Mg) ribbon in air

• Materials: Magnesium ribbon, tongs, Bunsen burner or spirit lamp, watch glass, water, red and blue litmus paper, sandpaper.
• Procedure:
  1. Clean the magnesium ribbon (about 2-3 cm) with sandpaper to remove the protective oxide layer.
  2. Hold the ribbon with tongs and heat its tip over a flame.
  3. Collect the white powder (ash) formed on a watch glass.
  4. Dissolve the ash in a small amount of water.
  5. Test the resulting solution with red and blue litmus paper.
• Observations:
  1. Magnesium ribbon burns with a dazzling white flame.
  2. A white powdery ash (Magnesium Oxide) is formed.
  3. The aqueous solution of the ash turns red litmus paper blue, indicating it is basic in nature. Blue litmus paper shows no change.
• Chemical Equations:
  • 2Mg (s) + O₂ (g) → 2MgO (s) (Magnesium Oxide)
  • MgO (s) + H₂O (l) → Mg(OH)₂ (aq) (Magnesium Hydroxide - basic)
• Conclusion: This is a Chemical Change because:
  • A new substance, Magnesium Oxide (and then Magnesium Hydroxide), is formed with different properties.
  • Light and heat are produced during the reaction.

Experiment 3(c): Reaction between Zinc (Zn) and dilute Sulphuric Acid (H₂SO₄)

• Materials: Zinc granules, dilute Sulphuric Acid, test tube, delivery tube (optional), soap solution (optional), matchstick or burning splinter.
• Procedure:
  1. Take a few zinc granules in a test tube.
  2. Carefully add dilute Sulphuric Acid to the test tube.
  3. Observe the reaction.
  4. Bring a burning matchstick or splinter near the mouth of the test tube (or pass the gas evolved through soap solution and bring the splinter near the soap bubbles).
• Observations:
  1. Bubbles of a colourless gas are evolved from the surface of the zinc granules.
  2. The test tube may feel warm.
  3. The gas burns with a 'pop' sound when a burning splinter is brought near it, confirming it is Hydrogen gas (H₂).
• Chemical Equation: Zn (s) + H₂SO₄ (aq) → ZnSO₄ (aq) (Zinc Sulphate) + H₂ (g) ↑
• Conclusion: This is a Chemical Change because:
  • A new substance, Hydrogen gas (along with Zinc Sulphate), is formed.
  • Evolution of gas is observed.

Experiment 3(d): Heating of Copper Sulphate (CuSO₄.5H₂O) crystals

• Materials: Copper Sulphate crystals (blue vitriol), test tube, Bunsen burner or spirit lamp, test tube holder, dropper, water.
• Procedure:
  1. Take a small amount of blue Copper Sulphate crystals in a dry test tube.
  2. Heat the test tube gently, holding it with a test tube holder.
  3. Observe the changes in the crystals and on the cooler parts of the test tube.
  4. Allow the residue to cool.
  5. Add a few drops of water to the residue.
• Observations:
  1. On heating, the blue colour of the crystals changes to a white powder (anhydrous Copper Sulphate).
  2. Tiny water droplets are seen condensing on the cooler, upper parts of the test tube.
  3. On adding water to the white residue, the blue colour is restored.
• Chemical Equation:
  • CuSO₄.5H₂O (s) (Blue Hydrated Copper Sulphate) --Heat→ CuSO₄ (s) (White Anhydrous Copper Sulphate) + 5H₂O (g) (Water Vapour)
  • CuSO₄ (s) + 5H₂O (l) → CuSO₄.5H₂O (s) (Blue colour restored)
• Conclusion: The heating process involves a Chemical Change because the water of crystallisation is removed, changing the chemical composition from hydrated copper sulphate to anhydrous copper sulphate (a new substance). Although adding water reverses the colour change (often cited as a characteristic of physical change), the initial heating step fundamentally altered the substance's composition by breaking chemical bonds associated with the water molecules.

Experiment 3(e): Reaction between Sodium Sulphate (Na₂SO₄) and Barium Chloride (BaCl₂) solutions

• Materials: Sodium Sulphate solution, Barium Chloride solution, two test tubes, beaker.
• Procedure:
  1. Take Sodium Sulphate solution in one test tube and Barium Chloride solution in another.
  2. Mix the two solutions (e.g., pour one into the other or mix in a beaker).
  3. Observe the change.
• Observations:
  1. Immediately upon mixing, a white, insoluble substance (precipitate) is formed.
  2. This white precipitate is Barium Sulphate (BaSO₄).
• Chemical Equation: Na₂SO₄ (aq) + BaCl₂ (aq) → BaSO₄ (s) ↓ (White Precipitate) + 2NaCl (aq) (Sodium Chloride)
• Conclusion: This is a Chemical Change because:
  • New substances (Barium Sulphate and Sodium Chloride) are formed.
  • Formation of an insoluble precipitate is a clear indicator of a chemical reaction (double displacement reaction).

General Precautions:

• Handle chemicals like acids carefully. Avoid direct contact.
• Use tongs or test tube holders when heating substances.
• Point the mouth of the test tube away from yourself and others, especially when heating or reacting substances that produce gases.
• Clean magnesium ribbon before burning.
• Do not look directly at the burning magnesium ribbon as the intense light can harm your eyes.
• Use small quantities of reactants.

Summary: Physical vs. Chemical Change

Multiple Choice Questions (MCQs):

1. Which of the following is an example of a physical change?
   a) Burning of magnesium ribbon
   b) Rusting of iron
   c) Melting of wax
   d) Reaction of zinc with acid

2. When iron nails are dipped in copper sulphate solution, the colour of the solution changes from blue to:
   a) Reddish-brown
   b) Light green
   c) Colourless
   d) Yellow

3. Burning of magnesium ribbon in air produces:
   a) Magnesium carbonate (white powder)
   b) Magnesium hydroxide (colourless solution)
   c) Magnesium oxide (white powder)
   d) Magnesium sulphate (white crystals)

4. The gas evolved when zinc granules react with dilute sulphuric acid is:
   a) Oxygen
   b) Carbon dioxide
   c) Hydrogen
   d) Sulphur dioxide

5. How is the presence of hydrogen gas typically confirmed in a laboratory test?
   a) It turns lime water milky.
   b) It extinguishes a glowing splinter.
   c) It burns with a 'pop' sound.
   d) It has a pungent smell.

6. Heating blue copper sulphate crystals results in the formation of:
   a) Black copper oxide
   b) Green copper carbonate
   c) White anhydrous copper sulphate
   d) Blue copper hydroxide

7. What is observed when solutions of sodium sulphate and barium chloride are mixed?
   a) Evolution of a gas
   b) Formation of a white precipitate
   c) A colour change to blue
   d) No observable change

8. A key difference between a physical change and a chemical change is that in a chemical change:
   a) The change is always easily reversible.
   b) Only the state of the substance changes.
   c) A new substance with different properties is formed.
   d) No energy change occurs.

9. Digestion of food in our body is an example of:
   a) Physical change only
   b) Chemical change
   c) Reversible change
   d) Both physical and chemical change, but primarily chemical

10. When heating copper sulphate crystals, water droplets appear on the cooler parts of the test tube. This water is known as:
    a) Distilled water
    b) Heavy water
    c) Water of crystallisation
    d) Mineral water

Answer Key for MCQs:

1. c) Melting of wax
2. b) Light green
3. c) Magnesium oxide (white powder)
4. c) Hydrogen
5. c) It burns with a 'pop' sound.
6. c) White anhydrous copper sulphate
7. b) Formation of a white precipitate
8. c) A new substance with different properties is formed.
9. b) Chemical change (or d, but chemical change is the primary aspect) - Let's stick with (b) as the best fit for typical exam questions focusing on the transformation.
10. c) Water of crystallisation

Study these notes thoroughly. Understanding the observations and conclusions for each experiment is key. Good luck with your preparation!