Problem 101 - A Complete Resource Book in Chemistry for JEE Main

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.

Step-by-Step Solution

Answer

The incorrect statement is (c). Ionic compounds conduct electricity in molten and aqueous states.

Step 1: Understand the characteristics of ionic compounds

Ionic compounds are made up of ions held together by strong electrostatic forces in a lattice structure. This gives them several distinct properties, such as high melting and boiling points, and the ability to conduct electricity when molten or dissolved in water.

Step 2: Analyze each statement

Examine each option to determine its correctness based on the known properties of ionic compounds. (a) Ionic compounds have high melting and boiling points due to strong ionic bonds. This statement is correct. (b) Ionic compounds, when dissolved in water, dissociate into ions which make the reactions relatively fast. This statement is generally correct. (c) Ionic compounds conduct electricity when in molten state or aqueous solution, as ions are free to move and carry charge. This statement is incorrect. (d) They are highly soluble in polar solvents, like water, due to the interaction between water's polar molecules and the ions. This statement is correct.

Step 3: Identify the incorrect statement

The task asks which statement is incorrect. From Step 2, we identified that statement (c) is incorrect because ionic compounds do conduct electricity when molten or dissolved in water.

Key Concepts

Ionic Bonding

Ionic bonding is all about the electrostatic attraction between charged ions. An ion is an atom or molecule that has lost or gained one or more electrons, so it has a net charge. In an ionic bond, one atom gives up one or more electrons to another atom. This loss or gain of electrons creates positively charged ions (cations) and negatively charged ions (anions). For example, sodium (Na) gives up one electron to become Na extsuperscript{+}, and chlorine (Cl) gains that electron to become Cl extsuperscript{-}.
These oppositely charged ions attract each other, forming a lattice of alternating ions. This lattice structure is very stable, which leads to some of the characteristic properties of ionic compounds.

• Strong Bonding: The strength of ionic bonds comes from the force of attraction between oppositely charged ions.
• Lattice Structure: The regular repeating pattern of ions gives ionic compounds their crystalline structure.

Understanding ionic bonds helps in predicting a compound’s behavior and properties, which is crucial when studying or working with different substances.

Electrolytes

Electrolytes are ionic compounds that dissociate into ions when dissolved in water, enabling the solution to conduct electricity. This property is due to the mobility of the ions in the solution. When an ionic compound like table salt (NaCl) is dissolved in water, the Na extsuperscript{+} and Cl extsuperscript{-} ions separate and disperse throughout the solution.
Here's why this is important:

• Conductivity: The ions in the solution allow the transfer of electrical current because they help carry charge.
• Biological Importance: Electrolytes are essential for many bodily functions, such as nerve signal transmission and muscle contractions.

Without electrolytes, the water or solution would not be able to conduct electricity effectively, which is contrary to the behavior described in option (c) from the exercise. This dissolution and conductivity form the basis for the designation of ions as electrolytes, which is why understanding them is crucial in both chemical and biological contexts.

Properties of Ionic Compounds

Ionic compounds have distinct properties that arise from their ionic bonds and crystal lattice structure. These properties can be observed in everyday substances such as table salt or baking soda.

• High Melting and Boiling Points: Due to the strong attraction between ions, a lot of energy is required to break these bonds, resulting in high melting and boiling points.
• Electrical Conductivity: As seen in option (c) of the exercise, ionic compounds can conduct electricity when melted or in aqueous solution because the ions are free to move.
• Solubility in Polar Solvents: Ionic compounds dissolve easily in polar solvents like water. This is because the positive and negative ends of the polar solvent molecules attract the ions and pull them into solution.

Their solubility, conductivity, and thermal properties are central to their function in industrial, biological, and environmental processes. These traits help distinguish ionic compounds from other types of substances, such as covalent compounds.