Question

Answer the following questions about the complexes $\mathrm{[NiCl_4]^{2-}}$ and $\mathrm{[Ni(CN)_4]^{2-}}$ :
(i) Write the hybridization involved in each case.
(ii) Which of them is the inner orbital complex and which one is the outer orbital complex ?
(iii) Compare their magnetic behaviour. [Atomic number : Ni = 28]

Hint:

Cl− weak field → sp³/outer/paramagnetic; CN− strong field → dsp²/inner/diamagnetic.

Answer 1

Concept: Whether the boiling point goes up or down depends on what the added substance does to the vapour pressure of the water. Boiling happens when the vapour pressure of the liquid becomes equal to the outside (atmospheric) pressure. If something lowers the vapour pressure, you need more heat to reach that point, so the boiling point rises. If something raises the vapour pressure, you reach that point sooner, so the boiling point falls.

Step 1: Adding KCl to water
KCl is a solid salt that does not turn into vapour, so we call it non-volatile. When it dissolves, its ions take up space at the surface and fewer water molecules can escape into the air. This lowers the vapour pressure of the water. Because the vapour pressure is now lower, you have to heat the solution to a higher temperature before it can boil. That is why the boiling point of water goes up.

Step 2: Adding methyl alcohol to water
Methyl alcohol is a liquid that evaporates easily, even more easily than water, so we call it volatile. When you mix it with water, it adds its own vapour to the space above the liquid. Now the total vapour pressure of the mixture is higher than that of pure water. Since the vapour pressure is higher, the mixture reaches the outside pressure at a lower temperature, so it boils sooner. That is why the boiling point goes down.

Answer: KCl is non-volatile, it lowers the vapour pressure, so the boiling point rises. Methyl alcohol is volatile, it raises the vapour pressure, so the boiling point falls.