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Foundations in medicine design > solutions > Flashcards

solutions Flashcards

1
Q

isssues affected by phase equilibria

A

whether an interface exists between 2 liquids

distribution of a drug between different media

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2
Q

how will a substance transfer (phase)

A

a substance will transfer spontaneously from a phase in which it has a higher chemical potential to a phase on which it has a lower chemical potential

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3
Q

what is a phase

A

the homogenous, physically distinct parts of a system are known as phases. these are separated from one another by interphases e.g. ice, water, water vapour

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4
Q

co-existence at phases

A

gases at equilibrium only one phase
liquid - miscible one phase immiscible 2 phases
solids- each solid is a separate phase unless a solid solution is formed as solutions only have one phase

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5
Q

the number of components in a system

A

the minimum number of independent species necessary to define the composition of all phases present in the system
e.g. ice water water vapour 3 phases one component

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6
Q

when does C = no of species

A

only when there is no chemical reaction

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7
Q

degrees of freedom

A

(F)number of factors which can be varied independently without noticeably altering the number of phases

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8
Q

what does phase rule tell us

A

the number of degrees of freedom for any particular number of components and phases in any system

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9
Q

what is Gibbs phase rule

A

P+F=C+2 at equilibrium
p is no of phases
c is no of component

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10
Q

a colligative property depends on the:

A

properties of the solvent
concentration (mole fraction) of the dissolved substance
number of particles of dissolved substance in the solution

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11
Q

4 main colligative properties

A

vapour pressure lowering
freezing point depression
boiling point elevation
osmotic pressure
(all thermodynamically related to each-other)
osmotic pressure has enormous importance as it contributes to flow of nutrients through biological cell walls and through plants

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12
Q

osmosis

A

tendency of solvent molecules to pass through a membrane from a more dilute toma more concentrated solution

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13
Q

what is osmotic pressure

A

if a solution is seperated from its solvent by a membrane then the excess pressure which has to be applied to prevent the flow of solvent is known as the osmotic pressure (uppercase pi)
osmotic pressure = RTx molarity

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14
Q

what is hydrostatic pressure

A

pressure exerted by a column of aqueous solution or water is called hydrostatic pressure

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15
Q

what is reverse osmosis

A

reverse osmosis is when a pressure (greater than osmotic pressure) is applied to the solution and forces the solvent through the membrane

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16
Q

types of membranes

A

semi permeable- permeable to solvent molecules only e.g. they will allow the passage of water but mot other molecules
biological (selectively permeable) these allow the passage of water and other molecules of low molecular weight but will restrain molecules of higher molecular weight

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17
Q

if red blood cells are immersed in solution of greater osmotic pressure than cells content:

A

water will pass out of cell to reduce chemical potential across cell membrane (cell shrinks)

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18
Q

if red blood cells immersed jn solution of lower osmoticpressure than cells content:

A

water will enter the cell (cell swells) and eventually lysis (cell breakdown) may occur

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19
Q

isotonic solutions

A

solutions between which there is no net flow of solvent when the solutions are prepared by a biological membrane are called isotonic - notably the RBC cell membrane

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20
Q

what must the effective osmotic pressure of a solution for injection be

A

approx same as blood serum
termed tonicity
not always same as osmolality

21
Q

importance of tonicity

A

injections- effect of surrounding medium on RBC

22
Q

tonicity in regards to osmotic pressure with blood serum

A

lower>hypotonic>cell swells, haemolysis may result
higher>hypertonic> cells shrink, crenation
same>isotonic>no net flow of liquid

23
Q

relationship between osmotic pressure and rate of infusion

A

the higher the osmotic pressure the slower the rate of infusion required

24
Q

relationships between colligative properties

A

as colligative properties are inter related it is impossible to determine one from the other
osmotic pressure is not easy to measure therefore makes use of other colligative properties to calculate e.g. freezing point depression
molality=moles/kg does not change with temp
molarity= moles/L changes with temp

25
Q

freezing point depression

A

this is the lowering of the freezing point of the solvent by adding a non volatile solute
e,g, add salt to roads to drop the freezing point of water in winter
delta Tf= Kf x m
kf is freezing point constant of the solvent
is concentration of solute

26
Q

converting Tf to osmotic pressure

A

at a given temp, osmotic pressure is proportional to change in Tf
also for dilute ideal solutions change in Tf is proportional to concentration

27
Q

what does solubility depend on

A

pressure, temperature,presence of salts and chemical reactions

28
Q

what is henrys law

A 
effect of pressure 
“the vapour pressure exerted by a gas dissolved in a solvent at constant temperature is proportional to the mole fraction of the gas”
pb=KhXb
Kh henrys law constant
Xa mole fraction of gas 
pa vapour pressure of gas
29
Q

effect of temperature on solutions

A

as temp increases, solubility of most gases decrease due to the greater tendency for the gas to expand

30
Q

what is salting out

A

salting out- gases are often liberated out of solution by addition of NaCl or sucrose
the solute added extracts the water molecules, reducing the density of the aqueous environment adjacent to the gas molecule

31
Q

micellar solubilisation

A

if gas molecules can be incorporated into the interior of micelles then this will increase solubility

32
Q

3 divisions of liquids in liquids

A

immiscible, partly miscible, completely miscible

33
Q

immiscible liquid mixtures

A

mo solution is formed
P+F=C+2
P=2 and C=2 so degrees of freedom =2
temp and conc. can be varied without necissarily changing number of phases

34
Q

completely miscible liquid mixture

A

solution is formed
P(1)+F=C(2)+2
F=3
temp, pressure and conc can be varies without necessarily moving from a single phase system

35
Q

partially miscible liquid mixture & phase behaviour observed (3)

A

no of phases can me 1 miscible or 2 immiscible
behaviour; solubility increases with an increase in temperature, solubility decreases with an increase in temperature, high solubility only at low or high temperatures

36
Q

what is critical temperature

A

above which both solutions are completely miscible

37
Q

what is the upper critical solution temperature

A

highest temp at which phase separation occurs
exists because the greater the thermal motion overcomes any potential energy advantage in molecules of one type being close together
above this temp both are fully miscible

38
Q

lower critical solution temperature

A

below which they mix in all proportions and above they form two products
at low temp two components are more miscible because they form a weak complex
at higher temp the complex breaks up and two components are less miscible

39
Q

what is the max value of F for a single component system

A

(C=1;P=2) therefore F=2

40
Q

systems where vapour phase is ignored and only solid and/or liquid phase are considered are termed

A

condensed systems

41
Q

eutectic point

A

represents the lowest temperature at which the liquid solution can exist

42
Q

what does solid dispersions enhance

A

the solid dispersions enhance the dissolution of poorly soluble drugs
the drug is mixed with a freely soluble “carrier” and enhanced dissolution is also related to particle size

43
Q

two main types of solids in solids

A

an intimate crystalline mixture of one component in the other

a solid solute dissolved in a solid solvent to give a mixed crystal, this is a true solid solution

44
Q

intimate crystalline mixtures - eutectic point

A

the eutectic point is the point at which the liquid and solid phases have the dame composition (eutectic composition)
the solid phase is an intimate mixture of fine crystals of the two compounds
when a mixture of 2 components with composition E are cooled, A and B crystallise out simultaneously

45
Q

mixed crystals

A

these involve a solid solute being dissolved in a solid solvent, generally these have minor component inserted into the structure of the host crystal
these solid solutions can exhibit higher, lower or unchanged melting behaviour

46
Q

difference between henrys and raoults law

A

raoults law applied to the solvent in a solution while henrys law applies to the solute in solution

47
Q

raoults law

A

the relative lowering of vapour pressure is equal to the mole fraction of the solute in solution

48
Q

solutions which obey raoults law are called

A

ideal solutions

49
Q

solutions which do not obey raoults law are called

A

real or non ideal solutions, most are this thpe

Foundations in medicine design (9 decks)

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