Composition of Freezing Point Crystals in a Glacial Acetic Acid Solution

[Tanishq Nandan]

Homework Statement

A solution contains 0.1mol of acetamide in 1Lit of glacial acetic acid.When the solution is cooled,the first crystal that appeared at the freezing point contains the molecules of
A.acetamide only
B.Acetic acid only
C.both acetamide and acetic acid
D.None

Homework Equations

Depression in freezing point=(molal depression constant)*(molality of solution)

The Attempt at a Solution

I don't see why there should be anything other than C.
It's a solution..consists of both solute and solvent,which have formed a composite mixture that freezes at the same temperature.So,shouldn't the crystal contain both of those components.
However,answer given is B

 

[Borek]

,which have formed a composite mixture that freezes at the same temperature

That would be an eutectic system, not every mixture works this way.

 

[Tanishq Nandan]

Oo..well,then how can we predict the answer for this question?

 

[Borek]

Just by looking at the melting points.

 

[Tanishq Nandan]

But..that isn't given in the question...and I don't think I'm supposed to remember the melting pt of either acetamide or acetic acid..

 

[Borek]

On the second thought - melting point would be the most important thing for mixture in which molar fractions of both substances involved are comparable. When concentration of the solute is much lower, its activity is also very low, so it can not freeze that easily.

I don't like the question, I am not convinced the answer is easy to give without additional information.

 

[Tanishq Nandan]

Ok,thank you