Question

Ionic solid conduct electricity in the molten state but not in the solid state because:
(a) In molten state free ions are loosely bound which are not free to move in solid-state.
(b) In solid-state ionic solids are hard, brittle and become soft in the molten state.
(c) All solid conduct electricity in the molten state
(d) In solid-state ions are converted to atoms which are insulators.

Answer 1

As we know in a molten state the ionic solid dissociates to its anion and cation that are positive and negative ions respectively these ions are responsible for conducting electricity. Use this idea to solve the question and get the correct answer.

Complete step by step answer:
The conduction of electricity through a solution involved the movement of charged particles. A solution of an ionic compound in water contains ions which can move to the oppositely charged electrodes when electricity is passed through a solution.
- Ionic compounds in solid-state do not conduct electricity because the movement of ions in solid is not possible due to their rigid structure.
- Ionic compounds conduct electricity in the molten state because in the molten state, since the electrostatic force of attraction between the oppositely charged ions is overcome due to the heat which is provided to the ionic solid to change it from solid-state to the liquid state.
- The heat provided weakens the electrostatic force of attraction between the ions and thus the ions move freely and conduct electricity.
- For example, when NaCl in the solid-state is heated then it decomposes to form a cation and anion as follows:
$NaC{{l}_{\left( s \right)}}\overset{Heat}{\mathop{\to }}\,Na_{\left( l \right)}^{+}+Cl_{\left( l \right)}^{-}$
This reaction is called the thermal decomposition reaction and after the solid NaCl is converted into molten NaCl, it can easily conduct electricity due to the free movement of $N{{a}^{+}}$ and $C{{l}^{-}}$ ions.

Hence option (a) is the correct one.

Note: Besides the molten state the ionic solid can conduct electricity when it is dissolved in water. Water is a polar solvent and it means that is has a charge separation which can be represented as: $\overset{+\delta }{\mathop{{{H}_{2}}}}\,\overset{-\delta }{\mathop{O}}\,$.
When an ionic solid is dissolved in water the negative pole of the water molecules attracts the positively charged cations in the ionic solid and similarly, the positive pole of the water molecule attracts the negatively charged anions in the ionic solid. Hence the ions become free to move and they can conduct electricity easily.