Acids, Bases and Salts

 

Concise notes on "Acids, Bases and Salts" for Class 10 Science, based on the NCERT curriculum and ideal for CBSE board preparation:

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🔹 Chapter: Acids, Bases and Salts

🧪 1. Acids

• Definition: Substances that release H⁺ ions in aqueous solution.

• Properties:

  • Sour taste

  • Turn blue litmus red

  • React with metal → H₂ gas

  • React with base → salt + water

• Types:

  • Strong acids: HCl, H₂SO₄, HNO₃

  • Weak acids: CH₃COOH, citric acid

• Examples:

  • HCl (hydrochloric acid)

  • H₂SO₄ (sulfuric acid)

  • HNO₃ (nitric acid)

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⚗️ 2. Bases

• Definition: Substances that release OH⁻ ions in aqueous solution.

• Properties:

  • Bitter taste

  • Soapy to touch

  • Turn red litmus blue

  • React with acid → salt + water

• Types:

  • Strong bases: NaOH, KOH

  • Weak bases: NH₄OH

• Examples:

  • NaOH (sodium hydroxide)

  • KOH (potassium hydroxide)

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🧫 3. Indicators

Substances that change color in acids and bases.

• Litmus: Red in acid, blue in base

• Methyl orange: Red in acid, yellow in base

• Phenolphthalein: Colorless in acid, pink in base

• Natural indicators: Turmeric, red cabbage

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🔄 4. Reactions of Acids and Bases

• Neutralization:

  $$\text{Acid + Base → Salt + Water}$$

• Acid + Metal → Salt + H₂ gas

  $$\text{2HCl + Zn → ZnCl₂ + H₂↑}$$

• Acid + Carbonate → Salt + H₂O + CO₂

  $$\text{2HCl + CaCO₃ → CaCl₂ + CO₂ + H₂O}$$

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🧮 5. pH Scale (0 to 14)

• <7: Acidic

• =7: Neutral

• >7: Basic

• Universal Indicator: Shows exact pH by color

• Importance of pH:

  • Soil pH for crops

  • pH in human body (7.35-7.45)

  • Tooth decay (acid below pH 5.5 damages enamel)

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🧂 6. Salts

• Formed by neutralization reaction

• Types:

  • Common salt (NaCl): From HCl + NaOH

  • Baking soda (NaHCO₃): Mild base, used in cooking

  • Washing soda (Na₂CO₃.10H₂O): Used in cleaning

  • Plaster of Paris (CaSO₄.½H₂O): Sets into hard solid on water addition

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🧪 7. Important Compounds and Their Uses

Compound	Chemical Formula	Use
Baking soda	NaHCO₃	Baking, antacid, fire extinguisher
Washing soda	Na₂CO₃·10H₂O	Laundry, softening hard water
Bleaching powder	CaOCl₂	Disinfecting water, bleaching
Plaster of Paris	CaSO₄·½H₂O	Making molds, fixing bones
Common salt	NaCl	Food preservative, raw material

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🔬 8. Water of Crystallization

• Fixed number of water molecules in salts.

• Example: CuSO₄·5H₂O (blue crystals), when heated → becomes white (CuSO₄)

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🔥 9. Test for Acid and Base

• Acid: Reacts with metal and carbonates

• Base: Soapy feel, changes red litmus to blue

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🌟 Important Points to Remember

• Acids produce H⁺ in water, bases produce OH⁻

• Strong acids and bases are corrosive

• pH is measured using universal indicator

• Salts are neutral but may have specific pH depending on parent acid/base

🔹 MCQs on Acids, Bases and Salts

1. Which of the following is a mineral acid?
   a) Citric acid
   b) Acetic acid
   c) Hydrochloric acid
   d) Tartaric acid
   → c) Hydrochloric acid

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2. The chemical formula of baking soda is:
   a) Na₂CO₃
   b) NaHCO₃
   c) CaCO₃
   d) NaOH
   → b) NaHCO₃

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3. A solution turns red litmus blue. Its pH is likely to be:
   a) 1
   b) 4
   c) 7
   d) 10
   → d) 10

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4. Which acid is present in vinegar?
   a) Formic acid
   b) Citric acid
   c) Acetic acid
   d) Oxalic acid
   → c) Acetic acid

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5. Which of the following is used in antacids?
   a) NaCl
   b) NaHCO₃
   c) HCl
   d) CH₃COOH
   → b) NaHCO₃

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6. Which gas is released when an acid reacts with a metal?
   a) Oxygen
   b) Nitrogen
   c) Hydrogen
   d) Carbon dioxide
   → c) Hydrogen

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7. Which of the following is a strong base?
   a) NH₄OH
   b) NaOH
   c) Mg(OH)₂
   d) Ca(OH)₂
   → b) NaOH

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8. The pH of a neutral solution is:
   a) 0
   b) 5
   c) 7
   d) 14
   → c) 7

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9. Which of these is used to disinfect drinking water?
   a) Plaster of Paris
   b) Bleaching powder
   c) Baking soda
   d) Washing soda
   → b) Bleaching powder

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10. When CO₂ is passed through lime water, it turns:
    a) Red
    b) Blue
    c) Milky
    d) Transparent
    → c) Milky

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11. The chemical name of washing soda is:
    a) Sodium carbonate
    b) Sodium bicarbonate
    c) Calcium carbonate
    d) Sodium chloride
    → a) Sodium carbonate

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12. Which base is used in soaps?
    a) HNO₃
    b) NaOH
    c) HCl
    d) H₂SO₄
    → b) NaOH

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13. Phenolphthalein gives a pink colour in:
    a) Neutral solution
    b) Acidic solution
    c) Basic solution
    d) Saline solution
    → c) Basic solution

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14. The chemical formula of Plaster of Paris is:
    a) CaSO₄·2H₂O
    b) CaSO₄·½H₂O
    c) CaCl₂
    d) CaCO₃
    → b) CaSO₄·½H₂O

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15. An example of an olfactory indicator is:
    a) Methyl orange
    b) Onion
    c) Phenolphthalein
    d) Litmus
    → b) Onion

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16. Which salt is formed by the reaction of HCl and NaOH?
    a) NaCl
    b) Na₂CO₃
    c) NaHCO₃
    d) Na₂SO₄
    → a) NaCl

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17. Tooth enamel gets corroded when pH of mouth drops below:
    a) 6.0
    b) 7.0
    c) 5.5
    d) 4.0
    → c) 5.5

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18. A strong acid completely:
    a) Evaporates in air
    b) Dissociates in water
    c) Turns red litmus blue
    d) Changes taste of base
    → b) Dissociates in water

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19. Common salt is obtained by evaporation of:
    a) Rain water
    b) River water
    c) Sea water
    d) Ground water
    → c) Sea water

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20. The pH of lemon juice is:
    a) Around 2
    b) Around 5
    c) Around 7
    d) Around 9
    → a) Around 2