Question

The phenol-water system has an upper critical solution temperature.
A. True
B. False

Answer 1

Hint: Upper critical solution temperature: The temperature above which the various components of a mixture in the solution are miscible in all proportions is called upper critical solution temperature. It is also called consolute temperature.
Complete step by step solution:
We know that phenol is an organic chemical and water is inorganic or aqueous chemical.
When we are going to mix phenol and water they won’t be miscible in one another. They would form two layers on each other. The upper layer would be water and the bottom layer would be phenol.
We know that organic and aqueous phases are not miscible with each other at room temperature.
Coming to the given system phenol-water, by increasing the temperature of the system the miscibility of the liquids increases slowly. The concentration of the water is high in the upper layer and the concentration of phenol is high in the lower layer till some temperature.

After crossing some temperature both layers will become miscible and form a single layer. That temperature where both the solvents are miscible one in another is called upper critical solution temperature (UCST).
For the phenol-water system upper critical solution temperature is 66.8\[^{o}C\].
So, the given statement is true.

Option A is correct.

Note: Don’t be confused between upper critical temperature and critical temperature.
The critical temperature of a chemical or compound is the temperature at and above which vapor of the chemical cannot be liquefied. It is not going to depend on how much pressure is applied. Every chemical has its own critical temperature.