Cheat Sheet: Acids, Bases and Salts | Science Class 10 PDF Download

Understanding Acids and Bases

1. Acids: Sour in taste, turn blue litmus red. Examples: HCl, H₂SO₄, HNO₃, CH₃COOH.

2. Bases: Bitter in taste, turn red litmus blue. Examples: NaOH, Ca(OH)₂, KOH, Mg(OH)₂, NH₄OH.

3. Indicators: Substances that show different colors in acidic and basic solutions.

• Natural Indicators: Litmus (purple in neutral, red in acid, blue in base), turmeric, red cabbage, flower petals (e.g., Hydrangea, Petunia, Geranium).
• Synthetic Indicators: Phenolphthalein (colorless in acid, pink in base), methyl orange (red in acid, yellow in base).
• Olfactory Indicators: Change odor in acidic or basic media (e.g., onion, vanilla, clove).

Chemical Properties of Acids and Bases

1. Reaction with Metals

(a) Acids: React with metals to produce salt and hydrogen gas.

• General Reaction: Acid + Metal → Salt + H₂(g)
• Example: H₂SO₄(aq) + Zn(s) → ZnSO₄(aq) + H₂(g)

Note: Test for H₂: Burns with a pop sound near a burning candle.

(b) Bases: Some bases (e.g., NaOH) react with certain metals (e.g., Zn) to form salt and hydrogen gas.

• Example: 2NaOH(aq) + Zn(s) → Na₂ZnO₂(s) + H₂(g) (Sodium zincate).

2. Reaction with Metal Carbonates/Hydrogencarbonates

Acids: Produce salt, carbon dioxide, and water.

Metal carbonate/hydrogencarbonate + Acid → Salt + CO₂(g) + H₂O(l)

• Na₂CO₃(s) + 2HCl(aq) → 2NaCl(aq) + H₂O(l) + CO₂(g)
• NaHCO₃(s) + HCl(aq) → NaCl(aq) + H₂O(l) + CO₂(g)

Note: Test for CO₂: Turns lime water [Ca(OH)₂] milky due to CaCO₃ formation; excess CO₂ forms soluble Ca(HCO₃)₂.

3. Reaction of Acids and Bases (Neutralization)

Acid reacts with base to form salt and water.

• General Reaction: Acid + Base → Salt + H₂O
• Example: NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
• Ionic Reaction: H⁺(aq) + OH⁻(aq) → H₂O(l)
• Observation: Phenolphthalein turns pink in base, colorless in acid.

4. Reaction of Metallic Oxides with Acids

Metallic Oxides: Act as bases, react with acids to form salt and water.

• Example: CuO(s) + 2HCl(aq) → CuCl₂(aq) + H₂O(l) (Blue-green solution).
• Conclusion: Metallic oxides are basic oxides.

5. Reaction of Non-Metallic Oxides with Bases

Non-Metallic Oxides: Act as acids, react with bases to form salt and water.

• Example: Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)
• Conclusion: Non-metallic oxides are acidic.

Commonality in Acids and Bases

(a) Acids: Produce H⁺(aq) or H₃O⁺ (hydronium ions) in water, responsible for acidic properties.

• Example: HCl + H₂O → H₃O⁺ + Cl⁻
• Dry HCl gas does not show acidic behavior (no H⁺ ions without water).

(b) Bases: Produce OH⁻(aq) ions in water; soluble bases are called alkalis.

• Examples: NaOH(s) → Na⁺(aq) + OH⁻(aq), KOH(s) → K⁺(aq) + OH⁻(aq)
• Conductivity: Acidic and basic solutions conduct electricity due to H⁺/H₃O⁺ or OH⁻ ions.
  Non-acidic hydrogen-containing compounds (e.g., glucose, alcohol) do not produce H⁺ ions, so they don’t conduct electricity.

Strength of Acids and Bases

(a) pH Scale: Measures H⁺ ion concentration (0–14).

• pH < 7: Acidic (higher H⁺ concentration, lower pH).
• pH = 7: Neutral (e.g., distilled water).
• pH > 7: Basic (higher OH⁻ concentration).

​​(b) ​​​Universal Indicator: Shows different colors for different pH values.

(c) Strong vs. Weak:

• Strong acids (e.g., HCl) produce more H⁺ ions; weak acids (e.g., CH₃COOH) produce fewer.
• Strong bases (e.g., NaOH) produce more OH⁻ ions; weak bases (e.g., NH₄OH) produce fewer.

(d) Dilution: Mixing acid/base with water is exothermic, reduces H₃O⁺/OH⁻ concentration per unit volume.

• Caution: Add acid to water slowly with stirring to avoid splashing or container damage.

Importance of pH in Everyday Life

• Biological Systems: Organisms function in a narrow pH range (e.g., human body: 7.0–7.8).
• Acid Rain: pH < 5.6, harms aquatic life by lowering river water pH.
• Soil pH: Plants require specific pH for growth; tested using universal indicator paper.
• Digestive System: Stomach produces HCl for digestion; excess acid causes indigestion, treated with antacids (e.g., Mg(OH)₂).
• Tooth Decay: Occurs when mouth pH < 5.5; prevented by basic toothpaste neutralizing acid from bacterial sugar degradation.
• Animal/Plant Defense: Bee stings (methanoic acid, acidic) treated with baking soda (base); nettle stings (methanoic acid) treated with dock plant leaves (basic).

Salts

1. Family of Salts

Definition: Salts with same positive or negative ions belong to a family.

• Examples: NaCl, Na₂SO₄ (sodium salts); NaCl, KCl (chloride salts).
• Common Salts: K₂SO₄, Na₂SO₄, CaSO₄, MgSO₄, CuSO₄, NaCl, NaNO₃, Na₂CO₃, NH₄Cl.

2. pH of Salts

• Neutral Salts: Formed from strong acid + strong base (pH = 7, e.g., NaCl).
• Acidic Salts: Strong acid + weak base (pH < 7, e.g., NH₄Cl).
• Basic Salts: Strong base + weak acid (pH > 7, e.g., Na₂CO₃).
• Testing: Check pH using universal indicator paper.

Sodium Hydroxide (NaOH)

• Process: Chlor-alkali process via electrolysis of aqueous sodium chloride (brine).

• Reaction:
  2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g)

• Electrolysis Products:

  1. Anode: Chlorine gas (Cl₂) released.

  2. Cathode: Hydrogen gas (H₂) released.

  3. Solution: Sodium hydroxide (NaOH) remains.

Bleaching Powder (Ca(OCl)₂ or CaOCl₂)

• Preparation: Reaction of chlorine gas with dry slaked lime.
  Ca(OH)₂(aq) + Cl₂(g) → CaOCl₂(aq) + H₂O(l)

• Uses:

  1. Bleaching cotton and linen in the textile industry.

  2. Oxidizing agent in various industries.

  3. Disinfectant for potable water by eliminating microorganisms.

Baking Soda (Sodium Bicarbonate, NaHCO₃)

• Preparation:
  NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃

• Reaction on Heating:
  2NaHCO₃ → Na₂CO₃ + H₂O + CO₂

• Uses:

  1. Component in baking powder (with tartaric acid), producing CO₂ to make bread/cake rise:
     NaHCO₃ + H⁺ → CO₂ + H₂O + Sodium salt of acid

  2. Neutralizes stomach acid as an antacid.

  3. Used in soda-acid fire extinguishers.

Washing Soda (Sodium Carbonate, Na₂CO₃·10H₂O)

• Preparation: Heating baking soda to form sodium carbonate, then recrystallization.
  Na₂CO₃ + H₂O → Na₂CO₃·10H₂O

• Uses:

  1. Used in glass, soap, and paper industries.

  2. Production of sodium compounds like borax.

  3. Cleaning agent for household use.

  4. Removes permanent water hardness.

• Water of Crystallization: Contains 10 water molecules per formula unit, making it hydrated.

Water of Crystallization

• Definition: Water molecules bound within a salt’s crystal structure.Salt Crystals

• Examples:

  1. Copper Sulfate (CuSO₄·5H₂O): Appears dry but contains water of crystallization. Heating removes water, turning it white; moistening restores blue color.

  2. Washing Soda (Na₂CO₃·10H₂O): Hydrated with 10 water molecules.

  3. Gypsum (CaSO₄·2H₂O): Contains 2 water molecules per formula unit.

• Crystallization: Formation of solid crystals with organized atomic/molecular structure via precipitation, freezing, or gas deposition.

• Examples of Crystals: Table salt (NaCl), sucrose (sugar), snowflakes, diamond, quartz.

Plaster of Paris (CaSO₄·½H₂O)

• Preparation: Heating gypsum to 100°C (373K).
  CaSO₄·2H₂O(s) → CaSO₄·½H₂O + 3/2H₂O

• Chemical Note: Two CaSO₄ units share one water molecule.

• Uses:

  1. Medical Casting: Forms sturdy casts for broken bones when mixed with water.
     Use of Plaster of Paris

  2. Sculpting and Art: Moldable for casts, masks, and decorative designs.

  3. Home Decoration: Used for wall accents, ceiling tiles, figurines, and crafts.