Class 9 Science Notes Chapter 4 (Chapter 4) – Lab Manual (English) Book

Alright class, let's focus on Chapter 4 from your Science Lab Manual. This chapter deals with crucial practical skills involving mixtures and their separation, as well as understanding different types of mixtures like solutions, suspensions, and colloids. These concepts are fundamental and often appear in various government exams, so pay close attention.

Chapter 4: Mixtures, Solutions, and Separation Techniques - Detailed Notes

Core Concepts:

• Mixture: A substance containing two or more elements or compounds that are not chemically bonded together. Mixtures can be homogeneous or heterogeneous.
• Homogeneous Mixture (Solution): Components are uniformly distributed, and the mixture has a uniform composition throughout (e.g., salt dissolved in water). Particle size is extremely small (< 1 nm).
• Heterogeneous Mixture: Components are not uniformly distributed and may be visible. Composition varies throughout (e.g., sand in water, oil and water). Particle size is larger. Suspensions and Colloids are types of heterogeneous mixtures.
• Separation Techniques: Methods used to separate components of a mixture based on differences in their physical properties (e.g., solubility, boiling point, density, magnetic properties, particle size, sublimation).

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.
• Materials:
  • For True Solution: Common salt (NaCl) or sugar, water.
  • For Suspension: Chalk powder or fine sand/soil, water.
  • For Colloid: Starch powder or milk, water.
  • Beakers, glass rods, filter paper, funnel, torch/laser pointer.
• Procedure:
  1. Prepare samples by dissolving/mixing the respective substances in water in separate beakers. Stir well.
  2. Observe the appearance (transparency).
  3. Test stability by leaving the mixtures undisturbed for some time.
  4. Test filterability by filtering each mixture through filter paper. Observe the filtrate and any residue.
  5. Test the Tyndall effect by passing a beam of light through each mixture in a dark place and observing the path of light from the side.
• Observations & Comparison Table:

• Key Concepts Tested: Homogeneous vs Heterogeneous, Particle Size, Stability, Filtration, Tyndall Effect.

Experiment 2: Separation of Mixture Components

A. Separating Mixture of Sand, Common Salt, and Ammonium Chloride (or Camphor)

• Aim: To separate the components of the given mixture using appropriate techniques.
• Principle: Utilizes differences in physical properties:
  • Ammonium chloride/Camphor sublimes (solid to gas directly) on heating.
  • Common salt is soluble in water, sand is insoluble.
  • Water can be evaporated to recover dissolved salt.
• Procedure:
  1. Sublimation: Gently heat the mixture in a china dish covered with an inverted funnel (plugged with cotton). Ammonium chloride/Camphor vaporizes and solidifies (sublimate) on the cooler inner walls of the funnel. Scrape off the sublimate.
  2. Dissolution & Filtration: Add water to the remaining mixture (sand and salt) in the china dish. Stir well to dissolve the salt. Filter the mixture. Sand remains on the filter paper (residue). The clear liquid collected is the filtrate (salt solution).
  3. Evaporation: Gently heat the filtrate in the china dish until all the water evaporates, leaving behind solid common salt.
• Observations: White sublimate collected. Insoluble sand left as residue. White salt crystals obtained after evaporation.
• Precautions: Heat gently during sublimation and evaporation. Ensure proper filtration setup.
• Key Concepts Tested: Sublimation, Solubility, Filtration, Evaporation, Heterogeneous Mixture.

B. Separating Mixture of Iron Filings and Sulphur Powder

• Aim: To separate iron filings from sulphur powder.
• Principle: Iron is magnetic, sulphur is not. Magnetic separation is used.
• Procedure: Spread the mixture on a sheet of paper. Roll a bar magnet (preferably covered in plastic wrap or paper for easy removal of iron) through the mixture.
• Observations: Iron filings get attracted to the magnet and stick to it. Sulphur powder is left behind.
• Key Concepts Tested: Magnetic Properties, Magnetic Separation, Heterogeneous Mixture.

C. Separating Dyes in Black Ink using Paper Chromatography

• Aim: To separate the different coloured components (dyes) present in black ink.
• Principle: Paper Chromatography. Separation occurs based on the difference in solubility of the dyes in the solvent (mobile phase) and their differential adsorption onto the filter paper (stationary phase). Components that are more soluble in the solvent and less adsorbed by the paper travel farther up the paper.
• Procedure:
  1. Draw a pencil line about 2-3 cm from one end of a filter paper strip.
  2. Put a small spot of black ink at the centre of the pencil line. Let it dry.
  3. Pour the solvent (e.g., water or an alcohol-water mixture) into a chromatography jar/gas jar to a depth of about 1 cm.
  4. Suspend the filter paper strip in the jar such that the ink spot is above the solvent level.
  5. Cover the jar and leave it undisturbed. Observe the solvent rising up the paper.
  6. Remove the strip when the solvent front is near the top. Mark the solvent front. Let it dry.
• Observations: As the solvent moves up, the ink spot separates into different coloured spots at different heights. Black ink is often a mixture of multiple dyes.
• Rf Value (Retention Factor): Rf = (Distance travelled by the component spot) / (Distance travelled by the solvent front). Each component has a characteristic Rf value for a given solvent and stationary phase.
• Key Concepts Tested: Chromatography, Adsorption, Solubility, Stationary Phase (filter paper), Mobile Phase (solvent), Rf Value, Mixture Composition.

D. Separating Mixture of Two Immiscible Liquids (e.g., Oil and Water)

• Aim: To separate a mixture of two immiscible liquids.
• Principle: Immiscible liquids do not mix and form separate layers based on their densities. A separating funnel is used.
• Procedure:
  1. Close the stopcock of the separating funnel.
  2. Pour the mixture (e.g., kerosene oil and water) into the funnel. Stopper it.
  3. Allow the mixture to stand undisturbed until distinct layers are formed. Water, being denser, forms the lower layer; oil forms the upper layer.
  4. Place a beaker below the funnel. Remove the stopper.
  5. Carefully open the stopcock and drain out the lower layer (water) into the beaker.
  6. Close the stopcock just as the upper layer reaches it.
  7. Place another beaker below and collect the upper layer (oil).
• Observations: Two clear layers are formed. The denser liquid settles at the bottom.
• Key Concepts Tested: Immiscibility, Density, Separating Funnel, Heterogeneous Mixture.

E. Separation of Miscible Liquids by Distillation (Conceptual Understanding)

• Principle: Used to separate mixtures of miscible liquids with sufficiently different boiling points (difference > 25°C). The liquid with the lower boiling point vaporizes first, its vapours are cooled (condensed) back into liquid, and collected separately.
• Apparatus: Distillation flask, thermometer, condenser, beaker.
• Process: The mixture is heated in the distillation flask. Vapours of the lower boiling point liquid rise, pass into the condenser where cold water circulates, condense into liquid, and are collected as distillate. The thermometer monitors the temperature of the vapours.
• Fractional Distillation: Used when the difference in boiling points is less than 25°C. Uses a fractionating column placed between the flask and condenser to provide more surface area for repeated vaporization and condensation cycles, leading to better separation.
• Key Concepts Tested: Boiling Point, Vaporization, Condensation, Distillation, Miscible Liquids, Homogeneous Mixture (Solution).

Multiple Choice Questions (MCQs)

1. Which separation technique is most suitable for separating ammonium chloride from a mixture of ammonium chloride and common salt?
   a) Filtration
   b) Evaporation
   c) Sublimation
   d) Magnetic Separation

2. In the chromatography of black ink, the component dye that travels the farthest on the filter paper is:
   a) Least soluble in the solvent
   b) Most adsorbed by the paper
   c) Most soluble in the solvent and least adsorbed by the paper
   d) Heaviest

3. A mixture of oil and water can be separated using:
   a) A filter paper
   b) A separating funnel
   c) A distillation apparatus
   d) A magnet

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

5. During the separation of sand, salt, and ammonium chloride, sand is separated by which process?
   a) Sublimation
   b) Evaporation
   c) Filtration (after dissolving salt in water)
   d) Magnetic separation

6. The principle behind separating iron filings from sulphur powder is based on the difference in their:
   a) Solubility
   b) Boiling points
   c) Magnetic properties
   d) Densities

7. A mixture where particles are large enough to settle down when left undisturbed is called a:
   a) True solution
   b) Colloid
   c) Suspension
   d) Homogeneous mixture

8. Distillation is used to separate liquids based on the difference in their:
   a) Densities
   b) Solubilities
   c) Particle sizes
   d) Boiling points

9. In paper chromatography, the filter paper acts as the:
   a) Mobile phase
   b) Stationary phase
   c) Solute
   d) Solvent

10. Which of the following is a homogeneous mixture?
    a) Milk
    b) Air (unpolluted)
    c) Soil
    d) Chalk powder in water

Answer Key:

1. c) Sublimation
2. c) Most soluble in the solvent and least adsorbed by the paper
3. b) A separating funnel
4. c) Milk
5. c) Filtration (after dissolving salt in water)
6. c) Magnetic properties
7. c) Suspension
8. d) Boiling points
9. b) Stationary phase
10. b) Air (unpolluted) - Note: Air is typically considered homogeneous at a macroscopic level.

Study these notes thoroughly, focusing on the principles and observations for each experiment. Good luck with your preparation!