More About Salts

In this section, we will explore the fascinating world of salts—how they are formed, their properties, and their applications in daily life. Let’s break it down step by step.

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Key Point 1: Family of Salts

Elaboration

• Salts are compounds formed when an acid reacts with a base in a neutralization reaction.
• Salts can be grouped into families based on their positive or negative radicals.
  • For example, sodium chloride (NaCl) and sodium sulphate (Na₂SO₄) belong to the family of sodium salts.
  • Similarly, NaCl and potassium chloride (KCl) belong to the family of chloride salts.

Examples

1. Sodium chloride (NaCl): A sodium salt and a chloride salt.
2. Magnesium sulphate (MgSO₄): A magnesium salt and a sulphate salt.
3. Copper sulphate (CuSO₄): A copper salt and a sulphate salt.

Activity: Identifying Families of Salts

Step-by-step Instructions

1. Write the chemical formulae of the given salts:
   • Potassium sulphate (K₂SO₄), Sodium sulphate (Na₂SO₄), Calcium sulphate (CaSO₄), etc.
2. Identify the acids and bases used to form these salts.
   • Example: Sodium chloride (NaCl) is formed from hydrochloric acid (HCl) and sodium hydroxide (NaOH).
3. Group the salts into families based on their positive or negative radicals.

Observations

• Sodium salts: NaCl, Na₂SO₄, Na₂CO₃.
• Chloride salts: NaCl, KCl.
• Sulphate salts: Na₂SO₄, CaSO₄, MgSO₄.

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Key Point 2: pH of Salts

Elaboration

• The pH of a salt depends on the strength of the acid and base that formed it.
  • Salts of strong acids and strong bases are neutral (pH = 7).
  • Salts of strong acids and weak bases are acidic (pH < 7).
  • Salts of weak acids and strong bases are basic (pH > 7).

Examples

1. Sodium chloride (NaCl): Neutral salt (formed from HCl and NaOH).
2. Aluminium chloride (AlCl₃): Acidic salt (formed from HCl and Al(OH)₃).
3. Sodium carbonate (Na₂CO₃): Basic salt (formed from H₂CO₃ and NaOH).

Activity: Testing pH of Salts

Step-by-step Instructions

1. Collect samples of salts like sodium chloride, sodium carbonate, and aluminium chloride.
2. Dissolve each salt in distilled water.
3. Test the solution with litmus paper and pH paper.

Observations

• Sodium chloride: Neutral (pH ~7).
• Sodium carbonate: Basic (pH >7).
• Aluminium chloride: Acidic (pH < 7).

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Key Point 3: Chemicals from Common Salt

Elaboration

• Common salt (sodium chloride, NaCl) is a raw material for many chemicals used in daily life.
• Through various processes, sodium chloride is converted into useful substances like sodium hydroxide, bleaching powder, baking soda, washing soda, and Plaster of Paris.

Examples

1. Sodium Hydroxide (NaOH): Produced through the chlor-alkali process.

   • Reaction: $$2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂$$
   • Uses: Soap manufacturing, paper production, and detergents.

2. Bleaching Powder (CaOCl₂): Used for disinfecting water and bleaching clothes.

   • Reaction: $$Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O$$
   • Uses: Water purification, textile bleaching.

3. Baking Soda (NaHCO₃): Used in cooking and as an antacid.

   • Reaction (on heating): $$2NaHCO₃ → Na₂CO₃ + H₂O + CO₂$$
   • Uses: Making soft cakes, neutralizing stomach acid.

4. Washing Soda (Na₂CO₃·10H₂O): Used in cleaning and softening hard water.

   • Reaction: $$Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O$$
   • Uses: Glass manufacturing, laundry detergent.

5. Plaster of Paris (CaSO₄·½H₂O): Used in medical casts and construction.

   • Reaction: $$CaSO₄·½H₂O + H₂O → CaSO₄·2H₂O$$
   • Uses: Supporting fractured bones, making decorative items.

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Key Point 4: Water of Crystallization

Elaboration

• Some salts contain fixed amounts of water molecules as part of their structure. This is called water of crystallization.
• Heating removes the water of crystallization, changing the salt's properties.

Examples

1. Copper sulphate (CuSO₄·5H₂O): Blue crystals turn white on heating.
2. Gypsum (CaSO₄·2H₂O): Loses water to form Plaster of Paris.

Activity: Heating Copper Sulphate

Step-by-step Instructions

1. Take a few crystals of blue copper sulphate in a dry boiling tube.
2. Heat the tube gently.
3. Observe the color change and look for water droplets inside the tube.
4. Add 2–3 drops of water to the heated crystals.

Observations

• Blue crystals turn white on heating.
• Water droplets form inside the tube.
• Adding water restores the blue color.

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Scenario-Based Questions

1. Scenario: You need to purify drinking water.

   • Question: Which compound would you use, and why?
   • Answer: Bleaching powder (CaOCl₂). It kills germs and makes water safe for drinking.

2. Scenario: You want to bake a cake but don’t have baking powder.

   • Question: Can you use baking soda instead? Why or why not?
   • Answer: Yes, baking soda can be used. It releases CO₂ gas when heated, making the cake fluffy.

3. Scenario: A farmer has hard water in his field.

   • Question: Which compound would help soften the water?
   • Answer: Washing soda (Na₂CO₃·10H₂O). It removes permanent hardness of water.

4. Scenario: A doctor needs to set a fractured bone.

   • Question: Which compound would the doctor use, and how does it work?
   • Answer: Plaster of Paris (CaSO₄·½H₂O). It hardens into gypsum when mixed with water, providing support to the bone.

5. Scenario: You accidentally spill acid on your skin.

   • Question: Which household item could you use to neutralize the acid?
   • Answer: Baking soda (NaHCO₃). It is a mild base and neutralizes the acid safely.

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