Lecture 4 Flashcards
What is the relationship between the number of phases and the number of degrees of freedom?
the more phases we have the less degrees of freedom we have.
How many degrees of freedom in a system of 3 components and 1 phase?
4
How can we simplify a 4 dimensional graph?
by making two variables constant. e.g. temperature and pressure.
now the only thing we have to worry about is the 2 concentrations
which diagram is used to show this?
the triangular diagram which describes the concentration of the 3 different components of the system.
the apex/corners of the triangles are 100%
The area of the triangle represents all the possible combinations of the 3 components.
Everywere on the line you have a constant ratio of 2 of the components but the 3rd component is changing
in a ternary phase diagram with a pair of partially miscible liquids, how many regions are there?
2,
1 region everything is completely miscible and the other region, everything is not miscible
How can we draw tie lines in this ternary phase triangluar diagram?
We can start at 100% water and add in bezene or vie versa.
why is the angle of the tie line not always horizontal in this case of a ternary phase diagram?
it depends on how miscible the substances are.
if the 3rd liquid has an equal effect on both immiscible liquids then the tieline might be parallel to the base
What is usually used as a constant and why?
pressure is fine to be a constant but temperature tends to vary a lot.
e.g. something at a certain phase at room temperature may be different inside the body at 37degrees
How can we study the effects of temperature on these systems?
we can construct these systems at different temperatures
what is the effect of temperature on the systems?
as temperature increases, the darker 2-phase region decreases because higher temperatures increase solubility so the one phase system increases
What does a solution require?
a solute and a solvent
what is a solute?
the substance that gets dissolved
what is a solvent
the substance that does the dissolving
Why cant you see clumps of a solutuion?
because it is a molecular dispersion
What does a molecular dispersion mean?
what has been dissolved has been broken apart to the level of indivdual molecules.
it is a 1 phase system where there are no boundaries or distinct regions
what types of solutes are there?
electrolytes and non-electrolytes
Why can electrolytes conduct electrcity?
Electrolytes ionise in water, they break apart into ions which are charged, so can conduct electricty
are most drugs electrolytes?
yes
what is the difference between strong electrolytes and weak electrolytes?
strong electrolytes completely ionise in water,
weak ones only partially ionise in water
Why are there huge implications for electrolytes and solutions?
for something to be absorbed into the body, it has to be in liquid
What are the properties of a good drug considering the stomach is an aqueous environment?
a good drug should be ionised as ionised substances dissolve better in aqueous solutions so is more likely to dissolve in your gastric contents, ECF or your eye
What must the drug cross if we want it to be absorbed into the body?
a lipid bilayer membrane.
What form of the drug dissolves better through the lipid bilayer membrane?
the unionised form as it is not charged
What are the implications for non electrolytes like progesterone?
it will not dissolve in gastric contents and hence not available in absoprtion but can cross the skin.
This is why trasdermal progesterone formulations exist.
It also has relevance to colligative proerpties
