Question

11. Which of the following compounds is NOT in the gaseous phase at \(25^{\circ}\text{C}\)?

• A. ClF
• B. BrF
• C. IF$_3$
• D. ClF$_3$

Hint:

In interhalogen compounds, lighter molecules (like ClF, BrF, ClF$_3$) are generally gases, while iodine-containing interhalogens (especially IF$_3$, ICl$_3$) tend to be solids due to stronger intermolecular forces..

Answer 1

The Correct Option is C

Concept: Interhalogen compounds are formed when two different halogen atoms react with each other. They are generally represented by the formula \( AX_n \), where \( n \) can be 1, 3, 5, or 7. The physical state of these compounds at room temperature \((25^{\circ}\text{C} \text{ or } 298\,\text{K})\) depends largely on molecular mass and intermolecular forces (Van der Waals forces). As atomic size increases, polarizability increases, leading to stronger dispersion forces and higher boiling points. Hence, lighter interhalogens tend to be gases, while heavier ones may be liquids or solids.

Step 1: Evaluating ClF (Chlorine monofluoride).
ClF is a small diatomic interhalogen compound with a very low boiling point (around \(-100^{\circ}\text{C}\)). Since room temperature is much higher than its boiling point, ClF exists as a gas at \(25^{\circ}\text{C}\).

Step 2: Evaluating BrF (Bromine monofluoride).
BrF is relatively less stable but, in general consideration, behaves as a low-boiling interhalogen species. Its boiling point is around room temperature, and it is treated as a gaseous species under standard conditions.

Step 3: Evaluating ClF$_3$ (Chlorine trifluoride).
ClF$_3$ has a boiling point of about \(11.7^{\circ}\text{C}\). Since \(25^{\circ}\text{C}\) is higher than its boiling point, it exists as a gas at room temperature.

Step 4: Evaluating IF$_3$ (Iodine trifluoride).
IF$_3$ contains iodine, a large atom with high polarizability, leading to strong intermolecular forces. As a result, IF$_3$ is a yellow solid at room temperature \((25^{\circ}\text{C})\) and is not gaseous.

Step 5: Conclusion.
Among the given options:
• ClF: gas at \(25^{\circ}\text{C}\)
• BrF: gas at \(25^{\circ}\text{C}\)
• ClF$_3$: gas at \(25^{\circ}\text{C}\)
• IF$_3$: solid at \(25^{\circ}\text{C}\) Therefore, IF_3 is NOT in the gaseous phase at 25^{\circ}C.