PS400 exam 4

Question 1

how does mass transfer occur?

Answer 1

via diffusion or convection

dispersion (diffusion + convection)

Question 2

what is convection and diffusion?

Answer 2

diffusion : Brownian motion & movement towards equilibrium
convection: mass flow of liquid

Question 3

what is mass transfer important for?

Answer 3

dissolution
crystallization
membrane transport
movement within dosage forms
pharmacokinetics

Question 4

what is the equation for mass transfer?

Answer 4

t= L^2/ 6D

t- time
L distance
D-diffusion coeff

Question 5

what does diffusion time depend on?

Answer 5

viscosity of solvent

Question 6

what t do gasses and solids have?

Answer 6

gasses have lower t
solids have higher t

Question 7

how does viscosity influence the diffusion coefficient and diffusion time?

Answer 7

increased viscosity–>
decreased diffusion coefficient–> increased diffusion time

Question 8

what is flux? recognize equation

Answer 8

net rate of a drug movement in a specific direction per area?

j= 1/A dm/dt (dissolution rate)

Question 9

in flux, what is the relationship between j and A?
what is the relationship between j & dm/dt and A & dm/dt ?

Answer 9

j and A are inversely proportional

j and dm/dt–> directly
A and dm/dt–> directly

Question 10

what is ficks 2nd law of diffusion under steady state conditions?

Answer 10

C= mx +b
j= constant

Question 11

what is ficks 1 law of diffusion equation?

Answer 11

j= -D dC/dx ( change in concentration)

j and dc/dx have opposite signs

Question 12

for ficks 2nd law of diffusion, concentration is linear with position until? what is it independent of?

Answer 12

untill the outside concentration is reached
independent of time

Question 13

what is drug concentration at tablet surface equal to at steady state?

Answer 13

drug solubility in the dissolution medium

Question 14

what is drug concentration at L equal to?

Answer 14

drug concentration in bulk solution , which is equal to 0 for sink conditions

Question 15

what is the noyes Whitney equation for dissolution rate?

Answer 15

dm/dt=DA (Cs-CL/L)

Question 16

how does particle size affect dissolution rate?

Answer 16

decrease size–> increase A
so increase dm/dt

Question 17

how does mixing of dissolution medium affect dissolution rate?

Answer 17

increasing in mixing–> decreases L
increases dm/dt

Question 18

how does viscosity of dissolution medium affect dissolution rate?

Answer 18

decrease ionic strength –> increase D
increase dm/dt

Question 19

how does increasing volume of dissolution medium affect dissolution rate?

Answer 19

increase V–> decrease Cl
increase dm/dt

Question 20

what is chemical kinetics and how do we apply it to pharmacy?

Answer 20

study of rate of chemical reactions

helps optimize stability & predicting shelf life based on degradation rate

Question 21

what are zero order kinetic equations?

Answer 21

A=Ao-kot and t1/2=A/2ko

Question 22

what are first order kinetic equations?

Answer 22

A=Aoe-k1t and t1/2=0.693/k1

Question 23

what order do suspensions follow?

Answer 23

zero order

Question 24

concentration of a solution remains constance because….

Answer 24

solid can go into solution to replace reacted drug

Question 25

what are elementary reactions?

Answer 25

have single transition/ activation state

Question 26

what are bimolecular reactions?

Answer 26

2 molecules reacting, most common

Question 27

what is transition theory used for?

Answer 27

to determine the energy required for reactants to reach the transition state

Question 28

what are the assumptions of transition state theory?

Answer 28

fast equilibrium between reactants and transitions state species

reaction rate is proportional to the concentration of the transition state species

Question 29

what is ionic strength?

Answer 29

measure of concentrations of ions in a solution

more ions—> higher ionic strength

Question 30

whether the rate constant of increases or decreases depends on the product of charges….. what happens when:
++ or –
+ 0 or - 0
-+ or +-

Answer 30

increase ionic strength and K

increase ionic stength reversible with K

increase ionic strength and decrease K

Question 31

what happens when ionic strength is low and high?

Answer 31

low: ions have large ionic atmospheres

high: ions in solution shield the ions or interest and the ion atmosphere reduces in size

Question 32

effect of ionic strength on reaction rate at high ionic strength?

Answer 32

like charges don’t repeal easily–> favoring products
(small ions atmosphere ar shield from seeing each other)

opposing charges attract each other less, favoring reactants

Question 33

effect of ionic strength of reaction rate at low ionic strength?

Answer 33

like charges more easily repel each other, favoring reactants
(large ion atmosphere see each other at greater distance)

opposing charges more essaying attract each other, favoring products

Question 34

what is dielectric constant?

Answer 34

measure of attraction/ repulsion between ions in a solution

Question 35

what happens to dielectric constant (e) when:
++ or –
+/- 0
-+

Answer 35

increase e and k or decrease when adding alcohol

no k effect, decrease e

increase e and dec k
or decrease e and inc k (add alcohol)

Question 36

what is the Arrhenius equation?

Answer 36

lnk=ln A- Ea/RT

Question 37

for a 10c reduction in temp, what happens at Ea=10k, 20k and 30k?

Answer 37

shelf life increases by:
2x, 3x, 6x

Question 38

for 20c reduction in temperature, shelf life increases at Ea=10k, 20k, 30k by:

Answer 38

4x, 9x, 36x

Question 39

what is accelerated stability studies?

Answer 39

determine shelf life done by measure stability at higher temps and predicting stability at storage temp thru extrapolation

Question 40

for accelerated stability studies, what do we measure at each temperature?

Answer 40

rate constant over a range of buffer concentrations, extrapolate to determine rate with no buffer

Question 41

what is step 1 and 2 of accelerated stability studies?

Answer 41

determine bufferless k at several temps at specified ph

plot ln kobs vs 1/T and extrapolate to desired shelf life temp to obtain K extrap

Question 42

Ph profile, what happens at low, high and int ph?

Answer 42

low: H catalyzes reaction (acid catalysis)

high: OH catalyzes

intermediate: buffering species catalyze reaction