This screencast is going to go over a phase diagram for a ternary system. We could take
something that is partially miscible with three species water, acetone and MIBK and
we could represent them here by this triangular phase diagram. Now it is important to notice
that this particular phase diagram is for a system where the temperature is 25 degrees
Celsius. Two things can happen when we mix these three species together in a liquid form.
One they could remain as a single phase or two they could separate into two phases. This
all depends on the amounts of each species in the solution. For example if we were to
make a solution that we will call solution A. We will say that it is 70% acetone, 10%
water and 20% MIBK. We could plot exactly where this solution is in the phase diagram. I'm going to use a highlighter to do this.
You could see that as we increase up towards the acetone the top of that triangle would
represent 100% acetone solution so 70% would be along this line. If we do the same thing for water a 10% solution
of water would be somewhere along this line. Then a 20% solution of MIBK just so happens
to fall where these two already intersect. We would represent this point, solution A,
right there. As you can see this is outside of this envelope region. We will call this
region 1. Whenever any solution falls in region 1 it stays as a single phase liquid. The other
thing that could happen is if we fall under that envelope. Let's make up a solution that
might do that. Let's say solution B is 33 % by mass (again all of this is by mass) acetone,
33% MIBK and 33% Water. Otherwise an equal mass ratio of all three species. When we look
at the lines here 33% is going to fall somewhere above that 30 line. MIBK is going to be somewhere
along their 30 line and water is somewhere above it's 30 line. This falls exactly dead
center of the triangle for this phase diagram. We'll draw that right around there. The trick here, as I mentioned, is that it separates into
two phases. These lines that you see are known as tie lines. They connect compositions of
the two liquid phases in equilibrium. You basically go to each side following those
tie lines as guides. If we do that we are going to come along here to this side and
up hereto this side. Just as a disclaimer reading any kinds of diagrams or plots can
be a little open to interpretation. Hopefully our answers are somewhat similar to each others.
This is going to be known as the water rich phase because it is heavy in water. This
is going to be known as the MIBK rich phase because it is obviously heavy in MIBK. Now
we read these two separate plots. For the MIBK it looks like about 53% MIBK. Then if
we read the acetone we are going up in the plot so we got 10, 20, 30, just under 40 so we'll say maybe about 38 wt%. At
this point you can just add them up to 1. If we go towards water wt% looks pretty good.
That is MIBK rich phase. The water rich phase we just go to the other side and it is about
I'm going to say 67% water and we go up towards acetone, so that's about, a little higher than 25,
somewhere between 25 and 30, so we'll say 28 wt% acetone. That leaves us with 5 wt% MIBK which is right
around that line. So, that looks pretty good. We started with the equal mass of each species and when they phase separate
and reach equilibrium at 25 degrees Celsius we get two phases with the following compositions.