Class 10 Notes

Class 10 Science Notes Chapter 2 (Chapter 2) – Lab Manual (English) Book

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Philoid

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Lab Manual (English)
Detailed Notes with MCQs of the practical aspects of Acids, Bases, and Salts as detailed in your Class 10 Science Lab Manual, Chapter 2. These experiments are fundamental and frequently appear in various government examinations, so pay close attention to the procedures, observations, and conclusions.

Chapter 2: Acids, Bases and Salts (Lab Manual Perspective)

Objective: To study the properties of acids (like HCl, H₂SO₄) and bases (like NaOH, Ca(OH)₂) through various reactions and tests conducted in the laboratory.

Key Concepts & Experiments:

  1. Identification using Indicators:

    • Aim: To test the effect of given acids and bases on different indicators.

    • Materials: Dilute HCl, Dilute H₂SO₄, Dilute NaOH solution, Lime water (Ca(OH)₂), Litmus solution/paper (Blue and Red), Phenolphthalein solution, Methyl Orange solution, Droppers, Test tubes.

    • Procedure: Take small samples of the given acid and base solutions in separate test tubes. Add a few drops of each indicator (or dip the litmus paper) into each solution.

    • Observations & Inferences:

      Indicator Effect of Acid (e.g., HCl) Effect of Base (e.g., NaOH)
      Blue Litmus Turns Red No Change
      Red Litmus No Change Turns Blue
      Phenolphthalein Colourless Turns Pink
      Methyl Orange Turns Red Turns Yellow

    • Conclusion: Indicators change colour depending on whether the solution is acidic or basic.

  2. Reaction of Acids with Metals:

    • Aim: To observe the reaction of acids with active metals like Zinc.
    • Materials: Zinc granules, Dilute HCl or Dilute H₂SO₄, Test tube, Delivery tube, Soap solution, Candle/Matchstick.
    • Procedure: Place a few zinc granules in a test tube. Add dilute acid. Observe the gas evolved. Pass the gas through soap solution to form bubbles. Bring a burning candle/matchstick near the gas-filled bubbles.
    • Observations: Brisk effervescence (gas bubbles) is observed. The gas burns with a 'pop' sound when a burning candle is brought near it.
    • Inference: Acids react with active metals to produce hydrogen gas (H₂).
    • Equation: Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g) ↑
    • Test for H₂ gas: Burns with a characteristic 'pop' sound.

  3. Reaction of Bases with Metals:

    • Aim: To observe the reaction of bases with metals like Zinc.
    • Materials: Zinc granules, NaOH solution, Test tube, Burner.
    • Procedure: Place a few zinc granules in a test tube. Add NaOH solution and warm gently. Test the gas evolved as in the previous experiment.
    • Observations: Effervescence occurs, and the gas evolved burns with a 'pop' sound.
    • Inference: Some strong bases react with certain active metals (like Zn, Al) to produce hydrogen gas.
    • Equation: Zn(s) + 2NaOH(aq) → Na₂ZnO₂(aq) [Sodium Zincate] + H₂(g) ↑
    • Note: All metals do not react with bases.

  4. Reaction of Acids with Metal Carbonates and Metal Hydrogen Carbonates:

    • Aim: To observe the reaction of acids with sodium carbonate (Na₂CO₃) and sodium hydrogen carbonate (NaHCO₃).
    • Materials: Solid Na₂CO₃, Solid NaHCO₃, Dilute HCl, Test tubes, Delivery tube, Lime water (Ca(OH)₂ solution).
    • Procedure: Take a small amount of Na₂CO₃ (or NaHCO₃) in a test tube. Add dilute HCl. Observe the gas evolved. Pass the gas through freshly prepared lime water using a delivery tube.
    • Observations: Brisk effervescence occurs. The gas turns lime water milky. If the gas is passed for a longer time, the milkiness disappears.
    • Inference: Acids react with metal carbonates and hydrogen carbonates to produce carbon dioxide gas (CO₂).
    • Equations:
      • Na₂CO₃(s) + 2HCl(aq) → 2NaCl(aq) + H₂O(l) + CO₂(g) ↑
      • NaHCO₃(s) + HCl(aq) → NaCl(aq) + H₂O(l) + CO₂(g) ↑
    • Test for CO₂ gas: Turns lime water milky due to the formation of insoluble calcium carbonate (CaCO₃).
      • Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) [White Precipitate/Milkiness] + H₂O(l)
    • Effect of Excess CO₂: CaCO₃(s) + H₂O(l) + CO₂(g) → Ca(HCO₃)₂(aq) [Calcium Hydrogen Carbonate - Soluble] - Milkiness disappears.

  5. Reaction of Acids and Bases (Neutralization):

    • Aim: To observe the reaction between an acid and a base.
    • Materials: Dilute NaOH solution, Dilute HCl solution, Phenolphthalein indicator, Test tube, Dropper.
    • Procedure: Take a small amount of dilute NaOH solution in a test tube. Add 1-2 drops of phenolphthalein indicator (solution turns pink). Add dilute HCl drop by drop, shaking gently, until the pink colour just disappears. Now add a drop of NaOH again.
    • Observations: The pink colour of the solution disappears on adding acid. The pink colour reappears on adding a drop of base again. The test tube may feel slightly warm.
    • Inference: Acids and bases react to neutralize each other's effect, forming salt and water. This reaction is called neutralization and is generally exothermic (releases heat).
    • Equation: NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l) + Heat

  6. Testing pH:

    • Aim: To determine the approximate pH of given solutions using pH paper or universal indicator.
    • Materials: Various solutions (e.g., dilute HCl, dilute NaOH, lemon juice, soap solution, water, dilute NaHCO₃ solution), pH paper strips or Universal Indicator solution, Droppers, White tile/Petri dish.
    • Procedure: Place a drop of each solution on separate strips of pH paper or add a few drops of universal indicator to small samples of each solution. Compare the colour produced with the standard pH colour chart.
    • Observations: Different solutions produce different colours corresponding to specific pH values.
      • Strong Acids (e.g., HCl): pH 1-3 (Red/Orange)
      • Weak Acids (e.g., Lemon Juice, Vinegar): pH 3-6 (Orange/Yellow)
      • Neutral (e.g., Pure Water, Sugar Solution): pH ≈ 7 (Green)
      • Weak Bases (e.g., NaHCO₃ solution, Soap): pH 8-11 (Greenish-Blue/Blue)
      • Strong Bases (e.g., NaOH): pH 11-14 (Blue/Violet)
    • Inference: pH scale (0-14) measures the acidity or basicity of a solution. pH < 7 is acidic, pH = 7 is neutral, pH > 7 is basic. Universal indicator gives a range of colours corresponding to different pH values.

  7. Water of Crystallization:

    • Aim: To study the effect of heat on hydrated salts like Copper Sulphate.
    • Materials: Copper Sulphate crystals (CuSO₄·5H₂O - Blue), Test tube, Bunsen burner, Test tube holder, Dropper, Water.
    • Procedure: Take a few blue crystals of copper sulphate in a dry test tube. Heat the test tube gently. Observe the changes in colour and state. Note if any water droplets form on the cooler parts of the test tube. Allow the residue to cool. Add a few drops of water to the residue.
    • Observations: On heating, the blue colour of crystals changes to a white powder. Tiny water droplets are seen on the cooler, upper parts of the test tube. On adding water to the white residue, the blue colour reappears, and heat may be released.
    • Inference: Hydrated salts contain a fixed number of water molecules associated with them, called water of crystallization. Heating removes this water, leading to an anhydrous salt (often with a different colour). Adding water restores the hydrated salt.
    • Equation: CuSO₄·5H₂O(s) [Blue] --(Heat)--> CuSO₄(s) [White Anhydrous] + 5H₂O(g)
      CuSO₄(s) + 5H₂O(l) → CuSO₄·5H₂O(s) [Blue] + Heat

Important Safety Precautions:

  • Always handle acids and bases with care, preferably using droppers.
  • Wear safety goggles.
  • If acid/base spills on skin, wash immediately with plenty of water.
  • When diluting concentrated acids, always add acid slowly to water with constant stirring, never water to acid (highly exothermic).
  • Use a test tube holder while heating. Point the mouth of the test tube away from yourself and others.
  • Handle chemicals judiciously; avoid wastage.

Multiple Choice Questions (MCQs):

  1. A student adds a few drops of universal indicator to a dilute solution of sodium bicarbonate taken in a test tube. Which of the following colours would be observed?
    (a) Red
    (b) Blue
    (c) Green
    (d) Yellow

  2. When zinc granules react with dilute sulphuric acid, a gas is evolved which burns with a 'pop' sound. This gas is:
    (a) Oxygen
    (b) Hydrogen
    (c) Carbon Dioxide
    (d) Sulphur Dioxide

  3. Lime water turns milky when carbon dioxide gas is passed through it due to the formation of:
    (a) Calcium Hydroxide
    (b) Calcium Carbonate
    (c) Calcium Bicarbonate
    (d) Calcium Oxide

  4. A solution turns red litmus blue. Its pH is likely to be:
    (a) 1
    (b) 4
    (c) 5
    (d) 10

  5. What happens when blue crystals of copper sulphate are heated in a dry test tube?
    (a) They turn red and water droplets are formed.
    (b) They remain blue but release water vapour.
    (c) They turn white and water droplets are formed.
    (d) They decompose to form copper oxide.

  6. Phenolphthalein indicator turns pink in which of the following solutions?
    (a) Dilute HCl
    (b) Lemon Juice
    (c) Dilute NaOH
    (d) Pure Water

  7. The reaction Zn(s) + 2NaOH(aq) → X + H₂(g) involves the formation of sodium zincate (X). What is the chemical formula of X?
    (a) NaZnO₂
    (b) Na₂ZnO
    (c) Na₂ZnO₂
    (d) NaZn(OH)₄

  8. A student observed that passing excess carbon dioxide through lime water first turned it milky and then the milkiness disappeared. This is because:
    (a) Calcium carbonate formed is soluble in water.
    (b) Calcium bicarbonate formed is soluble in water.
    (c) Calcium hydroxide is reformed.
    (d) The reaction reverses on passing excess CO₂.

  9. Which of the following substances will turn methyl orange indicator yellow?
    (a) Vinegar
    (b) Soap solution
    (c) Gastric juice
    (d) Car battery acid

  10. The process where an acid completely reacts with a base to form salt and water is called:
    (a) Displacement
    (b) Decomposition
    (c) Neutralization
    (d) Oxidation

Answer Key for MCQs:

  1. (b) Blue (Sodium bicarbonate is a weak base, pH > 7, typically 8-9)
  2. (b) Hydrogen
  3. (b) Calcium Carbonate
  4. (d) 10 (Bases turn red litmus blue, pH > 7)
  5. (c) They turn white and water droplets are formed.
  6. (c) Dilute NaOH
  7. (c) Na₂ZnO₂
  8. (b) Calcium bicarbonate formed is soluble in water.
  9. (b) Soap solution (Bases turn methyl orange yellow)
  10. (c) Neutralization

Study these notes thoroughly, focusing on the observations and chemical equations. Understanding these practical aspects is crucial for your exams. Good luck!

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