Ionic Compounds

Ionic compounds are formed by the combination of positively charged ions (cations) and negatively charged ions (anions). These compounds, such as sodium chloride (NaCl) or copper sulphate (CuSO₄), exhibit unique electrical properties based on their state and environment.

General Properties of Ionic Compounds:

1. Solid and Hard Structure

Ionic compounds exist in the solid state due to strong electrostatic forces between oppositely charged ions. They are hard but also brittle, meaning they can break under pressure.

2. High Melting and Boiling Points

The strong ionic bonds require large amounts of energy to break. This results in high melting and boiling points.

Melting and boiling points of some ionic compounds:

3. Solubility

• Soluble in Water: Water molecules help separate the ions, allowing ionic compounds to dissolve.
• Insoluble in Non-Polar Solvents: Ionic compounds do not dissolve in substances like kerosene or petrol, as these solvents cannot replace the original ionic attraction.

4. Electrical Conductivity

• Solid State: Does not conduct electricity because ions are tightly held in a rigid lattice and cannot move freely.
• Molten or Dissolved State: Conducts electricity because ions become free to move.
• Electrolyte Property: When dissolved in water or melted, ionic compounds dissociate into free ions, allowing them to complete an electric circuit and conduct electricity.

This property is widely used in chemistry, biology, and industrial applications.

5. Crystalline Nature

Ionic compounds form well-structured crystals due to the orderly arrangement of ions. The crystal structure depends on the size and charge of the ions.

Ionic compounds are made up of two parts:

1. Cations: positively charged ions, also called basic radicals.
2. Anions: negatively charged ions, also called acidic radicals.

These ions are held together by a strong force of attraction called the ionic bond, which forms because opposite charges attract each other. Each ionic bond is created by the attraction between one positive charge on a cation and one negative charge on an anion.

In the experiment, it was observed that the aqueous solutions of compounds like NaCl, CuSO₄, H₂SO₄, and NaOH conduct electricity.

Dissociation of ions

1. Nature of the Compounds:

• NaCl and CuSO₄ are salts.
• H₂SO₄ is a strong acid.
• NaOH is a strong base.

These compounds dissociate almost completely in water, producing large numbers of cations (positively charged ions) and anions (negatively charged ions).

2. Dissociation in Aqueous Solutions:

When these compounds dissolve in water, their molecules break apart into free-moving ions. For example:

• Sodium chloride (NaCl): NaCl→Na⁺+Cl⁻.
• Copper sulphate (CuSO₄): CuSO₄→Cu²⁺+SO₄²⁻.
• Sulphuric acid (H₂SO₄): H₂SO₄→2H⁺+SO₄²⁻.
• Sodium hydroxide (NaOH): NaOH→Na⁺+OH⁻

3. Mobility in Liquid State:

A unique property of liquids is that their particles are mobile and can move freely. In an aqueous solution:

• Cations (positive ions) move towards the cathode (negative electrode).
• Anions (negative ions) move towards the anode (positive electrode).

4. Conduction of Electricity:

This movement of ions towards their respective electrodes completes the electrical circuit, allowing the solution to conduct electricity. Therefore, the presence of a large number of dissociated ions in a solution ensures high electrical conductivity.

• Liquids or solutions containing a large number of dissociated ions, such as salts, strong acids, and strong bases, are good conductors of electricity.
• In contrast, non-electrolytes (e.g., glucose or urea) do not dissociate into ions, and their solutions cannot conduct electricity effectively.

1. Aim: To study the properties of ionic compounds, including their melting behaviour and electrical conductivity in aqueous solutions.

2. Requirements

• Apparatus: metal spatula, burner, carbon electrodes, beaker, electric cell, lamp, press key, electrical wires.
• Chemicals: sodium chloride (NaCl), potassium iodide (KI), barium chloride (BaCl₂), distilled water.

3. Procedure

Melting Test:

• Place a small amount of a salt sample on a metal spatula.
• Heat it using a burner and observe whether it melts.
• Repeat for other salts (NaCl, KI, BaCl₂).

Electrical Conductivity Test:

• Prepare an electrolytic cell by filling a beaker with salt solution.
• Insert carbon electrodes into the solution and connect them to an electric circuit (cell, lamp, press key).
• Close the circuit and observe if the lamp glows, indicating conductivity.
• Repeat with different salt solutions.

To verify the properties of ionic compounds

4. Observations

• Melting Test: Ionic compounds have high melting points and do not melt easily.
• Conductivity Test: The lamp does not glow in solid salts but glows in aqueous solutions, indicating that ionic compounds conduct electricity when dissolved or molten.

5. Conclusion: Ionic compounds are hard and have high melting points due to strong electrostatic forces. They do not conduct electricity in solid form, as ions are fixed in a lattice. They conduct electricity in molten or dissolved states because ions become mobile and act as electrolytes.