Class 9 Science Notes Chapter 1 (Chapter 1) – Lab Manual (English) Book

Alright class, let's get straight into the practical aspects covered in the first chapter of your Class 9 Science Lab Manual. These experiments form the foundation for understanding key scientific concepts and are often tested in various government exams. Pay close attention to the procedures, observations, and the principles behind them.

Chapter 1: Basic Laboratory Techniques & Experiments on Matter

This chapter typically introduces you to the laboratory environment and covers fundamental experiments related to the properties of matter, focusing on mixtures and changes of state.

Experiment 1: Preparation and Properties of True Solutions, Suspensions, and Colloids

• Aim: To prepare and differentiate between true solutions, suspensions, and colloidal solutions based on their properties like transparency, stability, filterability, and Tyndall effect.

• Materials Required:

  • Substances: Common salt (or sugar), fine sand (or chalk powder), starch (or milk/egg albumin).
  • Solvent: Water.
  • Apparatus: Beakers (or test tubes), glass rod for stirring, filter paper, funnel, torch/laser pointer.

• Procedure Summary:

  1. Take three beakers and label them A, B, and C.
  2. Add a small amount of common salt to beaker A, sand to beaker B, and starch to beaker C.
  3. Add water to each beaker and stir well using a glass rod.
  4. Observe the appearance (transparency/opaqueness) of each mixture.
  5. Leave the mixtures undisturbed for some time and observe their stability (whether particles settle down).
  6. Filter each mixture using filter paper and a funnel. Observe if any residue is left on the filter paper and the appearance of the filtrate.
  7. Pass a beam of light (from a torch) through each mixture in a dark place and observe if the path of light is visible (Tyndall effect).

• Observations:

  Property	True Solution (Salt/Sugar in Water)	Suspension (Sand/Chalk in Water)	Colloid (Starch/Milk in Water)
  Appearance	Transparent	Opaque	Translucent
  Stability	Stable (particles don't settle)	Unstable (particles settle down)	Stable
  Filterability	Passes through filter paper (no residue)	Particles retained on filter paper	Passes through filter paper
  Tyndall Effect	Does not show	May show (if particles large enough) or not	Shows
  Particle Size	< 1 nm	> 100 nm	1 nm - 100 nm

• Inferences/Conclusions:

  • True Solution: Homogeneous mixture, particles are extremely small, stable, does not scatter light.
  • Suspension: Heterogeneous mixture, particles are large enough to be seen, unstable (settle down), can be separated by filtration, may scatter light.
  • Colloid: Appears homogeneous but is heterogeneous, particle size is intermediate, stable, scatters light (Tyndall effect), cannot be separated by simple filtration.

• Precautions:

  • Use clean beakers and glass rods.
  • Stir the mixtures well.
  • Allow sufficient time for particles to settle in suspensions.
  • Observe the Tyndall effect in a dark environment for clarity.

Experiment 2: Determination of the Melting Point of Ice

• Aim: To determine the melting point of ice.
• Materials Required: Crushed ice, beaker, laboratory thermometer (-10°C to 110°C range), tripod stand, wire gauze, Bunsen burner (or spirit lamp), glass stirrer, clamp stand.
• Procedure Summary:
  1. Set up the apparatus: Place the beaker on the wire gauze kept on the tripod stand.
  2. Fill the beaker about halfway with crushed ice.
  3. Suspend the thermometer using a clamp stand such that its bulb is completely immersed in the ice, ensuring it doesn't touch the bottom or sides of the beaker.
  4. Record the initial temperature of the ice.
  5. Start heating the beaker gently using the burner on a low flame.
  6. Stir the ice-water mixture continuously with the glass stirrer.
  7. Record the temperature every half minute or minute.
  8. Note the temperature when the ice starts melting. Continue heating and recording the temperature until all the ice has melted into water.
  9. Observe the temperature readings carefully during the phase transition (melting).
• Observations: The temperature of the ice initially rises until it reaches 0°C (at standard atmospheric pressure). Then, the temperature remains constant at 0°C while the ice is melting, even though heat is continuously supplied. Once all the ice has melted, the temperature of the water starts to rise again.
• Inferences/Conclusions:
  • The constant temperature at which a solid changes into its liquid state at atmospheric pressure is called its melting point.
  • The melting point of pure ice is 0°C (or 273.15 K).
  • The heat energy supplied during melting is used to overcome the forces of attraction between the ice particles and change the state from solid to liquid. This hidden heat is called the Latent Heat of Fusion.
• Precautions:
  • The thermometer bulb should be completely surrounded by ice and should not touch the beaker walls or bottom.
  • Stir the mixture gently and continuously for uniform heat distribution.
  • Keep your eye level with the mercury level while reading the thermometer.
  • Use crushed ice for better contact with the thermometer bulb.

Experiment 3: Determination of the Boiling Point of Water

• Aim: To determine the boiling point of water.
• Materials Required: Distilled water, round bottom flask (or beaker), laboratory thermometer, tripod stand, wire gauze, Bunsen burner, clamp stand, pumice stones.
• Procedure Summary:
  1. Set up the apparatus similar to the melting point experiment, using a round bottom flask or beaker placed on the wire gauze.
  2. Take distilled water in the flask/beaker (about half full).
  3. Add a few small pieces of pumice stone to ensure smooth boiling (prevents bumping).
  4. Suspend the thermometer using a clamp stand so that its bulb is well immersed in the water but does not touch the bottom or sides.
  5. Record the initial temperature of the water.
  6. Heat the water using the burner, initially gently, then strongly.
  7. Stir if using a beaker (not usually needed with a flask and pumice stones).
  8. Record the temperature every minute.
  9. Note the temperature when the water starts boiling vigorously and bubbles rise throughout the bulk of the liquid.
  10. Continue heating and observe if the temperature remains constant during boiling.
• Observations: The temperature of the water rises steadily until it reaches 100°C (at standard atmospheric pressure). The temperature then remains constant at 100°C while the water is boiling and converting into steam, despite the continuous supply of heat.
• Inferences/Conclusions:
  • The constant temperature at which a liquid changes into its gaseous state (steam) at atmospheric pressure is called its boiling point.
  • The boiling point of pure water is 100°C (or 373.15 K) at standard atmospheric pressure (1 atm).
  • The heat energy supplied during boiling is used to overcome the forces of attraction between water molecules and change the state from liquid to gas. This hidden heat is called the Latent Heat of Vaporization.
  • Note: Boiling point changes with pressure (decreases at higher altitudes where pressure is lower) and is affected by impurities (dissolved impurities usually increase the boiling point).
• Precautions:
  • Add pumice stones before heating to avoid bumping. Never add them to hot water.
  • The thermometer bulb should be immersed in water, preferably slightly below the surface, but not touching the container.
  • Ensure the water boils vigorously before noting the constant temperature.
  • Keep your eye level with the mercury level for accurate readings.

Key Concepts Summary:

• Solution: Homogeneous mixture of two or more substances. (e.g., salt in water)
• Solute: Substance dissolved in a solvent. (e.g., salt)
• Solvent: The component of a solution that dissolves the solute (usually present in larger quantity). (e.g., water)
• Suspension: Heterogeneous mixture where solute particles do not dissolve but remain suspended and eventually settle down. (e.g., sand in water)
• Colloid: A mixture where particles are intermediate in size between those in solutions and suspensions, dispersed evenly throughout another substance. (e.g., milk, starch solution)
• Tyndall Effect: Scattering of a beam of light by particles in a colloid or a fine suspension.
• Melting Point: The constant temperature at which a solid turns into a liquid at atmospheric pressure.
• Boiling Point: The constant temperature at which a liquid turns into a gas (vapor) at atmospheric pressure.
• Latent Heat: Heat absorbed or released during a change of state without any change in temperature. (Latent heat of fusion for melting, latent heat of vaporization for boiling).

Multiple Choice Questions (MCQs):

1. Which of the following will show the Tyndall effect?
   a) Salt solution
   b) Sugar solution
   c) Starch solution
   d) Copper sulphate solution

2. During the determination of the melting point of ice, the temperature remains constant at 0°C because:
   a) Heat is not supplied
   b) Ice is a bad conductor of heat
   c) The supplied heat is used to overcome intermolecular forces (Latent Heat of Fusion)
   d) The thermometer is faulty

3. While determining the boiling point of water, pumice stones are added to:
   a) Increase the boiling point
   b) Decrease the boiling point
   c) Ensure smooth boiling and avoid bumping
   d) Make the water boil faster

4. A student prepares mixtures of (i) chalk powder in water, (ii) common salt in water, and (iii) milk in water. Which mixture(s) will leave a residue on the filter paper after filtration?
   a) Only (i)
   b) Only (ii)
   c) Only (iii)
   d) Both (i) and (iii)

5. Which statement is true for a true solution?
   a) It is heterogeneous.
   b) Its particles settle down on standing.
   c) Its particles scatter light.
   d) It is always transparent.

6. The correct procedure for reading a laboratory thermometer involves keeping the eye:
   a) Above the mercury level
   b) Below the mercury level
   c) Level with the mercury level
   d) At any convenient angle

7. What is the approximate particle size range for colloids?
   a) Less than 1 nm
   b) Between 1 nm and 100 nm
   c) Greater than 100 nm
   d) Greater than 1000 nm

8. If the atmospheric pressure decreases (e.g., at high altitudes), the boiling point of water will:
   a) Increase
   b) Decrease
   c) Remain the same
   d) First increase then decrease

9. Which of the following is NOT a recommended precaution while determining the melting point of ice?
   a) Stir the ice-water mixture continuously.
   b) Ensure the thermometer bulb touches the bottom of the beaker for faster heating.
   c) Keep the eye level with the mercury mark while reading.
   d) Use crushed ice.

10. Milk is an example of a:
    a) True Solution
    b) Suspension
    c) Colloid (Emulsion type)
    d) Homogeneous Mixture

Answer Key for MCQs:

1. c) Starch solution
2. c) The supplied heat is used to overcome intermolecular forces (Latent Heat of Fusion)
3. c) Ensure smooth boiling and avoid bumping
4. a) Only (i)
5. d) It is always transparent.
6. c) Level with the mercury level
7. b) Between 1 nm and 100 nm
8. b) Decrease
9. b) Ensure the thermometer bulb touches the bottom of the beaker for faster heating.
10. c) Colloid (Emulsion type)

Study these experiments and concepts thoroughly. Understanding the 'why' behind each step and observation is crucial. Good luck with your preparation!