Question

The freezing point of a solution containing 0.2g of acetic acid in 20.0g benzene is lowered by \[{{0.45}^{\circ }}C\]. The degree of association of acetic acid in benzene is: [Assume acetic acid dimerizes in benzene and \[{{K}_{f}}\] for benzene = \[5.12\,K\,kg\,mo{{l}^{-1}}\]]
A.) 94.5%
B.) 54.9%
C.) 78.2%
D.) 100%

Answer 1

Hint: The freezing point of any element is the temperature it changes from a liquid to a solid.
Which depends on the natural temperature -15 to 45 degrees the element is, a solid, liquid or gas. Iron for example is solid at this range of temperatures.

Complete answer:
\[\Delta T=ikmp\]
\[i=(1+\alpha )\]
\[0.45=(1-\alpha )(5.12)\left( \dfrac{\dfrac{\dfrac{0.2}{60}}{20}}{1000} \right)\]
\[(1-\alpha )=\dfrac{0.45\times 60\times 20}{5.12\times 0.2\times 1000}\]
\[1-\alpha =0.56\]
\[\alpha =0.54\]
\[=54.9\]
Van’t Hoff introduced a factor as ‘i’ called Van’t Hoff’s factor, for expressing the total extent of association or dissociation of solutes in any solution.

It is the ratio of the normal and any observed molecular masses of the solute, i.e., In any case of association, observed molecular mass that is being more than the normal, the factor i has a value of less than 1.

But in the case of the dissociation, the Van’t Hoff’s factor is more than 1 just because the molecular mass that has been observed has a lesser value than any of the normal molecular mass.

Note: Helium is a gas and water are a solid at -15 degrees, liquid above its freezing point of 0 degrees. Above the natural temperature at 100 degrees, it boils away into a gas. There is only 100 degrees between the freezing point and boiling point of water.
This is because it's natural freezing point is within the Earth’s natural temperature range. This range is above sea level. Much greater temperatures exist nearer the core of the Earth. If you then look at steel it's freezing point is 1370 degrees C and its boiling point is around 2750 degrees C where steel turns into a gas.