Question

For two ionic solids $CaO $ and $KI$, identify the wrong statement among the following.

• A. Lattice energy or CaO is much larger than that of KI
• B. KI is soluble in benzene
• C. KI has lower melting point
• D. CaO has higher melting point

Answer 1

The Correct Option is B

The question requires identifying the incorrect statement regarding the ionic solids calcium oxide (CaO) and potassium iodide (KI). Let's analyze each statement:

1. Lattice energy of CaO is much larger than that of KI: Lattice energy is the energy released when ions come together to form a crystalline lattice. CaO consists of Ca²⁺ and O²⁻ ions, whereas KI consists of K⁺ and I⁻ ions. The lattice energy is usually larger for compounds with higher charges on the ions and smaller ionic sizes. CaO, having divalent ions, indeed has a larger lattice energy than KI, which has monovalent ions. Hence, this statement is correct.
2. KI is soluble in benzene: Solubility in solvents is influenced by the principle "like dissolves like." KI is an ionic compound and is polar, while benzene is a non-polar solvent. Ionic and polar solutes do not dissolve in non-polar solvents like benzene. Therefore, the statement that KI is soluble in benzene is incorrect.
3. KI has a lower melting point: The melting point of a substance is influenced by the strength of its lattice energy. Since CaO has a high lattice energy, it is expected to have a higher melting point, while KI with its lower lattice energy will have a lower melting point. Hence, this statement is correct.
4. CaO has a higher melting point: This is a complementary statement to the previous one. CaO's higher lattice energy results in a higher melting point compared to KI. Hence, this statement is also correct.

Thus, the statement "KI is soluble in benzene" is the incorrect one because KI, being an ionic compound, doesn't dissolve in a non-polar solvent like benzene.