Lecture 4

Question 1

What is the relationship between the number of phases and the number of degrees of freedom?

Answer 1

the more phases we have the less degrees of freedom we have.

Question 2

How many degrees of freedom in a system of 3 components and 1 phase?

Answer 2

4

Question 3

How can we simplify a 4 dimensional graph?

Answer 3

by making two variables constant. e.g. temperature and pressure.

now the only thing we have to worry about is the 2 concentrations

Question 4

which diagram is used to show this?

Answer 4

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

Question 5

in a ternary phase diagram with a pair of partially miscible liquids, how many regions are there?

Answer 5

2,

1 region everything is completely miscible and the other region, everything is not miscible

Question 6

How can we draw tie lines in this ternary phase triangluar diagram?

Answer 6

We can start at 100% water and add in bezene or vie versa.

Question 7

why is the angle of the tie line not always horizontal in this case of a ternary phase diagram?

Answer 7

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

Question 8

What is usually used as a constant and why?

Answer 8

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

Question 9

How can we study the effects of temperature on these systems?

Answer 9

we can construct these systems at different temperatures

Question 10

what is the effect of temperature on the systems?

Answer 10

as temperature increases, the darker 2-phase region decreases because higher temperatures increase solubility so the one phase system increases

Question 11

What does a solution require?

Answer 11

a solute and a solvent

Question 12

what is a solute?

Answer 12

the substance that gets dissolved

Question 13

what is a solvent

Answer 13

the substance that does the dissolving

Question 14

Why cant you see clumps of a solutuion?

Answer 14

because it is a molecular dispersion

Question 15

What does a molecular dispersion mean?

Answer 15

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

Question 16

what types of solutes are there?

Answer 16

electrolytes and non-electrolytes

Question 17

Why can electrolytes conduct electrcity?

Answer 17

Electrolytes ionise in water, they break apart into ions which are charged, so can conduct electricty

Question 18

are most drugs electrolytes?

Answer 18

yes

Question 19

what is the difference between strong electrolytes and weak electrolytes?

Answer 19

strong electrolytes completely ionise in water,

weak ones only partially ionise in water

Question 20

Why are there huge implications for electrolytes and solutions?

Answer 20

for something to be absorbed into the body, it has to be in liquid

Question 21

What are the properties of a good drug considering the stomach is an aqueous environment?

Answer 21

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

Question 22

What must the drug cross if we want it to be absorbed into the body?

Answer 22

a lipid bilayer membrane.

Question 23

What form of the drug dissolves better through the lipid bilayer membrane?

Answer 23

the unionised form as it is not charged

Question 24

What are the implications for non electrolytes like progesterone?

Answer 24

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

Question 25

What is bioavailability?

Answer 25

how much of the administered drug reaches your systemic circulation
often expressed as a %

Question 26

What is electrolysis?

Answer 26

where a certain potential is applied which causes a current to generate a redox reaction.
However it cannot be used for anything that’s unionised as they cannot conduct electrolysis

Question 27

in a solution what does the dissolving?

Answer 27

the solute. this could be either the gas, liquid or solid

Question 28

Is air a solution?

Answer 28

yes as we have many gases and they are molecularly dispersed into one another. There is no phase boundary

Question 29

in pharmaceutics, which kind of solutions are we most interested in?

Answer 29

solutions where the solvent (dissolving agent) is liuid

Question 30

What is an example of solid in liquid solution?

Answer 30

mixing a cup of tea with sugar

Question 31

what is an example of a liquid liquid solution?

Answer 31

mixing alcohol and water

Question 32

what is an example of a gas in liquid solution

Answer 32

a can of coke which has CO2 in the liquid, completely dissolved

Question 33

Can a solute be filtered out from a solution?

Answer 33

no.
you can filter out big grains of something but a solution is a molecular dispersion so you cant filter out individual molecules.

Question 34

What other criteria are there of a solution?

Answer 34

the particles are always in motion
the volumes are not additive.
the 2 things you dissolve can have quite different properties
the dissolving agent appears in a greater extent, and the solute appears to a lesser extent
you may have more than one type solute or solvent

Question 35

What is molarity (M)?

Answer 35

the number of moles in 1L of solution

Question 36

what is molality (m)?

Answer 36

the number of moles per 1000g of solvent

Question 37

What is the relationship between molality and molarity in the example of water?

Answer 37

molarity = molality

however in other solutions, 100g of solvent does NOT = 1L

Question 38

what is % by weight?

Answer 38

the number of g per 100g of solution

Question 39

what is % by volume?

Answer 39

the number of ml per 100ml of solution

Question 40

What is 0.154M NaCl important to us?

Answer 40

it is isontonic saline, isotonic to our bodies

Question 41

What is ideal?

Answer 41

what theoretical scientists want

• no properties to change other than dilution
• no heat
• no expansion or shrinkage
• we want the constitutive properties to be the weighted averages of the individual constituents
• to be formed by mixing substances of similar properties.
• complete uniformity of attractive forces

Question 42

what happens when real solutions are mixted together?

Answer 42

there is a change of some sort, usually evolution of heat

Question 43

what is Raoult’s law?

Answer 43

if the solution is ideal, the partial vapour pressure of each volatile constituent is equal to the vapour pressure of the pure constituent multiplied by its mole fraction in the solution

Question 44

What is abvoe the surface of liquid water?

Answer 44

a vapour pressure of molecules

Question 45

What is the mole fraction?

Answer 45

the fraction of moles of a substance in that solution

Question 46

What is the vapour pressure composition curve?

Answer 46

Y axis = vapour pressure on both sides
X axis = mole fraction
at 100% B, vapour pressure is all due to B
When you mix the two solutions in the middle, the total vapour pressure is a weighted pressure of the 2 components of the solution

Question 47

What is the unit of vapour pressure?

Answer 47

psi