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💡 Salt vs sugar
Salt dissolves in water and its solution lights the bulb; sugar dissolves too but the bulb stays dark. The type of bond decides how a compound behaves.
In this Activity, we will compare the solubility and electrical conductivity of ionic and covalent compounds.
- Collect samples: camphor, sodium chloride, copper sulfate, sugar, naphthalene.
- Test solubility of each in (i) water, (ii) kerosene, (iii) petrol; record in Table 9.2.
- Set up carbon/metal electrodes with a 9 V battery and a bulb (Fig. 9.15).
- Test conductivity of each sample in the solid state and dissolved in water; note if the bulb glows.
- Group the compounds that show similar properties.
What we observe
Ionic compounds (NaCl, copper sulfate) dissolve in
water
and their solutions
conduct
. Covalent compounds (camphor, naphthalene) dissolve in
kerosene/petrol
and generally
do not conduct
.
Why don’t ionic compounds conduct electricity in the solid state?
- In the solid, ions are held in fixed positions by strong forces.
- To conduct, ions must be free to move .
- When dissolved in water (or melted), the ions become free → the solution conducts .
| Compound | Experiments | ||||
|---|---|---|---|---|---|
| Solubility in | Electrical conductivity of compounds in | ||||
| water | kerosene | petrol | solid state | water | |
| Camphor | Insoluble | Soluble | Soluble | No | No |
| Sodium chloride | Soluble | Insoluble | Insoluble | No | Yes |
| Copper sulfate | Soluble | Insoluble | Insoluble | No | Yes |
| Sugar | Soluble | Insoluble | Insoluble | No | No |
| Naphthalene | Insoluble | Soluble | Soluble | No | No |
Ionic vs Covalent Compounds
Ionic compounds
Covalent compounds
Soluble in water, not in kerosene/petrol
Usually insoluble in water, soluble in kerosene/petrol
Conduct when dissolved/molten (free ions)
Generally do not conduct (no free ions)
High melting and boiling points
Low melting and boiling points
Example: NaCl, copper sulfate
Example: camphor, naphthalene, sugar
⏸▶ Pause and Ponder
- 19. A solid that does not conduct as a solid but conducts when dissolved has an ionic bond .
- 20. Metal M with 2 valence electrons + oxygen → (i) formula MO , (ii) ionic bond, (iii) its aqueous solution conducts electricity.
NCERT Question 14 — Assertion (A): Copper sulfate conducts
Assertion (A): Copper sulfate conducts electricity in the molten state but not in the solid state. Reason (R): Copper and sulfate ions are fixed in the lattice in molten state, while in solid state they can move freely. Choose the correct option: (i) Both A and R are true, and R is the correct explanation of A. (ii) Both A and R are true, but R is not the correct explanation of A. (iii) A is true, but R is false. (iv) A is false, but R is true.
View Answer →
Important Definitions
- Solubility — ionic compounds dissolve in water; most covalent compounds dissolve in kerosene or petrol.
- Electrical conductivity — ionic compounds conduct when dissolved or molten; covalent compounds generally do not.
