Question

Which of the following statement is not correct regarding the properties of ionic compounds? (a) Ionic compounds have high melting and boiling points (b) Their reaction velocity in aqueous medium is very high. (c) Ionic compounds in their molten and aqueous solutions do not conduct electricity. (d) They are highly soluble in polar solvents.

Short answer

Statement (c) is not correct.

Step-by-step solution

Understand Ionic Compounds

Ionic compounds consist of positively and negatively charged ions. The strong electrostatic attraction between these ions results in various distinctive properties of ionic compounds.

Evaluate Melting and Boiling Points

Ionic compounds typically have high melting and boiling points due to strong ionic bonds that require a lot of energy to break. Thus, statement (a) is correct.

Assess Reaction Velocity

In aqueous solutions, ions are free to move, which generally results in faster reactions compared to solid states. Therefore, statement (b) is correct.

Analyze Electrical Conductivity

Ionic compounds conduct electricity in molten and aqueous states because ions are free to move and conduct current. Therefore, statement (c) is incorrect.

Check Solubility

Ionic compounds are typically soluble in polar solvents because the solvent molecules can stabilize the ions. Thus, statement (d) is correct.

Key concepts

Melting and Boiling Points

When discussing ionic compounds, an important aspect to consider is their melting and boiling points. Due to the nature of ionic bonds, these compounds generally have high melting and boiling points. An ionic bond is the force that holds opposite charges together; this force is very strong. Consequently, it requires a significant amount of energy to overcome these bonds.

For example, common table salt (NaCl) has a melting point of about 801°C and a boiling point of 1413°C, both of which are much higher than those of many covalent compounds. The reason for this difference lies in the inherent strength of ionic bonds. It takes a lot of heat energy to disrupt the electrostatic forces holding the ions together in a solid lattice, which is why such high temperatures are necessary to melt or boil ionic substances. This characteristic is why statement (a) in the original exercise is correct.

Electrical Conductivity

The ability of a substance to conduct electricity hinges on the presence of charged particles that can move freely. Ionic compounds are made up of cations and anions - positive and negative ions - that can move under certain conditions.

In a solid state, ionic compounds do not conduct electricity because their ions are locked firmly in place within the crystal lattice structure. However, when these compounds are melted or dissolved in a polar solvent like water, the rigid structure breaks down. As a result, the ions are free to move, which allows them to carry an electric current. This is why ionic compounds are good conductors of electricity in their molten and aqueous states.

When teaching or understanding electrical conductivity, it's crucial to remember the role of free-moving ions. This understanding corrects statement (c) from the original exercise, which incorrectly notes that ionic compounds do not conduct electricity in these states.

Solubility in Polar Solvents

Ionic compounds have a particular affinity towards polar solvents like water, which plays a significant role in their solubility properties. The reason lies in the ability of polar solvents to stabilize ionic compounds.

Polar solvents have molecules with partial positive and negative charges. Water, for instance, has a partial negative charge near the oxygen atom and a partial positive charge near the hydrogen atoms. When an ionic compound is introduced to a polar solvent, the solvent molecules interact and stabilize the ions in solution. The positive end of the solvent aligns with the anions, and the negative end aligns with the cations.

This interaction between solvent and ions reduces the electrostatic forces holding the ionic lattice together, allowing the compound to dissolve. This is why statement (d) in the exercise is true; ionic compounds typically dissolve well in polar solvents due to these stabilizing interactions.