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184 Cards in this Set
- Front
- Back
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bohr's theory of atomic structure
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extra-nuclear electrons revolve around the nucleus in well-defined orbits that are assigned quantum numbers counting outward from nucleus. electron absorbs a quantum of energy and moves to a higher energy orbital, when it falls back it emits radiation energy
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energy of orbitals related to frequency of radiaton emitted/absorbed by atom
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delta E= E2-E1=hv, difference of energy is in ergs, h is plank's constant (6.624x10^-24 erg sec), v is frequency. can be written as delta E=hc/lambda, where lamda is wavelengh and c is speed of light
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valence bond theory
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valence is relative power of atoms to bind, related to # of unpaired electrons in outer orbital.
electrovalent compounds-complete transfer of electrons covalent compounds-sharing of electrons |
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molecular orbital theory
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two atoms brought together, orbital coalesce to produce new molecular orbitals that surround nuclei of entire molcule
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binding forces between molecules
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repulsive and attractive, van der Waal's, ion-dipole and ion-induced dipole, hydrogen bonds
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repulsive and attractive forces
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as molecules are brought closer opposite charges attract one another, when the outer charge clouds touch molecules repel each other like rigid elastic bodies so they don't completely unify to become one entity
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van der Waal's forces
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dipole-dipole (keesom), dipole-induced dipole (debye), induced dipole-induced dipole (london)
potential energy of attraction varies inversely with separation, r^6, potential energy of repulsion changes more rapidly with distance |
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ion-dipole and ion-induced dipole forces
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account in part for the solubility of ionic crystalline substances in H2O, the cation attracting neg. oxygen atom and the anion attracting pos. hydrogen atoms of dipolar water molecule. involved in formation of iodide complex, where potassium iodide makes iodine soluble
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hydrogen bonds
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between a molecule containing hydrogen and a strongly electronegative atom like oxygen, nitrogen, or fluorine.
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change of state
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solid to gas-sublimation
gas to solid-deposition solid to liquid-melting liquid to solid-freezing or fusion gas to liquid-condensation liquid to gas-vaporization |
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kinetic theory of gases
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1.molecules are in random motion, frequently collisions result in pressure 2.collisions are elastic, no loss of energy, no attraction or repulsion
3.large intermolecular distance, defining characteristic is volume 4.increase temp is increase in kinetic energy and random motion |
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ideal gas
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follows the assumptions of the kinetic theory of gases
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3 factors used to characterize gases
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pressure, volume, temperature
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boyle's law
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inverse relationship of pressure and volume at constant temp. PV=k where k is a constant, or P=1/V
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law of gay-lussac and charles
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volume and temp are directly proportional when pressure is constant. V=T or V/T=k where k is constant
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ideal gas relationship
or combined gas law |
P1V1/T1=P2V2/T2
or PV=nRT where n is number of moles and R is the gas constant |
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real gases
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volume can be considered negligible only at high temps and low pressure, particles of gas only show no attraction or repulsion at low pressures, collisions aren't perfectly elastic.
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van der Waal's equation for real gases
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{P + an^2/V^2}(V-nb)= nRT
where a/V^2 accounts for internal pressure resulting from intermolecular forces of attraction and b accounts for the incompressibility of the molecules |
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liquification
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gas converted to liquid under pressure or with cooling
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critical temperature
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temperature above which a gas cannot be liquified no matter how high the pressure. at high pressure a supercritical fluid is formed
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pharmaceutical aerosols
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drug is dissolved/suspended in propellant that is liquid under pressure, when pressure is released by depressing valve the propellant vaporizes into atmosphere and drug alone is sprayed out.
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aerosol propellants
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fluorinated hydrocarbons, nitrogen or carbon dioxide gas
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relationship between vapor pressure and temperature
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clausius-clapeyron equation
log P2/P1=delta Hv(T2-T1)/2.303RT1T2 where P1 and P2 are vapor pressures at temps T1 and T2, delta Hv is molar heat of vaporization |
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vapor pressure at 100 C and delta Hv of water
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1 atm and 9720 calories/mole
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crystalline solids
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most favorable thermodynamic state, molecules arranged in ordered 3-dimensional state called lattice, ex. ice, sodium chloride, menthol
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properties of crystalline solids
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melting point, heat of fusion, polymorphism,solvates and hydrates
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melting point
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temp at which solid/liquid are at equilibrium
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heat of fusion
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heat absorbed when one gram of solid melts or heat liberated when one gram of liquid freezes. 80 cal/g of water at 0 degrees
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changes in freezing or melting point with pressure
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clapeyron equation: delta T/delta P=T(Vl-Vs/delta Hf)
delta Hf= molar heat of fusion Vl=volume liquid Vs=volume solid |
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polymorphism
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having more than one crystalline form, such as carbon or sulfur, with different melting points, x-ray diffraction patterns, solubilities
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solvates and hydrates
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during crystallization these compounds have a tendency to trap fixed molar ratio of solvent molecule. if the solvent is H2O it is a hydrate. ex. gallium nitrate 9 H2O per molecule and nafarelin acetate (each decapeptide has 1-2 acetic acid molecule, 2-8 H2O)
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amorphous solids
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do not contain an ordered lattice structure. like supercooled liquids, random molecular organization. ex.glass, pitch, synthetic plastics. tend to flow with pressure and don't have defined melting point
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properties of amorphous solids
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1.glass transition state=Tg midpoint of transition from glassy to rubber state
2.viscosity=tendancy to flow under shear stress |
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isotropic
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exhibits similar properties in all directions, amorphous solids and cubic crystals are isotropic
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novobiocin acid
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poorly absorbed and has no therapeutic activity in crystalline form, amorphous form readily absorbed and active
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liquid crystals
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mesophase-intermediate mobility. 2 types smectic-soap or grease like and nematic-thread like. in general molecules are organic, elongated and rectilinear, rigid, and strongly dipolar or easily polarizable
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phase rule
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F=C-P+2 c=components, p=phases f=degrees of freedom
+1 when it is a condensed system(ignoring vapor phase) |
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phase
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homogeneous, physically distinct portion of a system that is separated from other portions by bounding surfaces
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CaCO3=CaO + CO2
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2 components needed to define the system, 3 phases. so F=2-3+2=1
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triple point
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all phases of water exist at equilibrium, 0.0098 C and 4.58 mmHg. no degrees of freedom.
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eutectic mixtures
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solid and liquid phases, eutectic point is when miscible liquid and immiscible solid phases exist in equilibrium, F=0. ex.salol-thymol and salol-camphor (6 degrees)
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solution types
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true-one phase system, <10 A particles
colloidal-10-5000 A coarse dispersion- >100 A |
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binary solutions
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2 components, solvent is in greater proportion unless:
1. one component is liquid, it is almost always solvent 2. water present is almost always solvent |
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colligative properties
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depend on number of particles: osmotic pressure, vapor pressure lowering, freezing point depression, boiling point elevation
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additive properties
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depend on sum of properties of constituents in a solution: ex. mass
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constitutive properties
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depend on arrangement of atoms within molecule, number and kind of atoms within molecule. ex. refraction of light, electrical properties, surface and interfacial characteristics, solubility
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examples of nonelectrolytes
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sucrose, glycerin, naphthalene, urea
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examples of weak electrolytes
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ephedrine and phenobarbital
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concentration expressions
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molarity for colligative, normality(gram equiv/liter solution) for ions, molality is most robust, doesn't change with temp, moles/1000 grams solvent, mole fraction relative proportion of moles, percent expressions
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equivalent weight
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atomic weight divided by valence
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ideal solutions
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complete uniformity of attractive forces, when formed no heat is evolved or absorbed, final volume is additive property
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examples of variation from ideal in solutions
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mix water and alcohol volume is less than the 2 separate volumes, mix ammonium chloride in water, solution becomes cold due to heat absorption
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raoult's law
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Pa=Pa0 x Xa Pa is partial pressure, Pa0 is pure vapor pressure and Xa is mole fraction
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negative deviation from raoult's law
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adhesive forces of attraction between solute and solvent molecules exceed cohesive forces between like molecules, observed partial pressure is lower than calculated by the law (ex.chloroform and acetone)
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positive deviation from raoult's law
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adhesive forces are smaller than cohesive forces, observed partial pressure is higher than calculated by the law (ex.benzene and ethyl alcohol, carbon disulfide and acetone, chloroform and ethyl alcohol)
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henry's law
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Psolute=ksoluteXsolute
defines partial pressure of the solute, raoult's law defines the solvent. k approaches p0 when the solution approaches ideal behavior |
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vapor pressure of volatile:nonvolatile solutions
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vapor pressure is provided solely by the solvent but is decreased by the nonvolatile solute proportional to number of molecules of solute
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elevation of boiling point
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delta Tb=kXsolute where k is constant, x is mole fraction, in dilute solutions: delta Tb=kbm, where m is molality
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ebullioscopic constant
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Kb the molal elevation constant, characteristic value for a solvent
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depression of freezing point
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delta Tf=Kfm, where m is molality, principle behind antifreeze manufacture. Kf is molal depression or cryoscopic constant
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van't hoff equation for osmotic pressure
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(pi symbol)V=nRT
where pi symbol is osmotic pressure. expresses proportionality between osmotic pressure, temp and conc. |
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van't hoff correction factor for electrolytes
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pi symbol=iRTc
value of i approaches number of ions a molecule dissociates into, c is concentration in moles per liter |
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drugs more active in ionized form
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anionic and cationic antibacterial and antiprotozoal agents
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drugs active as nonelectrolytes
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hydroxybenzoate esters (parabens) and many general anesthetics
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drugs active in both ionized and nonionized forms
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sulfonamides
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degree of dissociation
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defined by van't hoff: conductance ratio-a=Vc/Vo (the V's are upside down) Vo is equivalent conductance at infinite dilution and Vc is number of particles present as ions at concentration c
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why are activity and activity coefficients necessary?
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electrostatic attraction and ion association in moderatly conc. solutions of strong electrolytes, values of colligative properties are less than expected.
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activity
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effective concentration of a solution of strong electrolytes that accounts for colligative properties. equals conc. at infinite dilution. actual conc. m/activity a is one at infinite dilution and is less than one at moderate dilution
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activity coefficient
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a/m where a is activity and m is actual concentration
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ionic strength
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lewis and randall introduced to relate interionic attractions and activity coefficients. u=1/2(the sum of cz^2 for all ions present)
c=conc. in moles/liter and z is valence |
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debye huckel theory
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logyi= -Az^2(square root of u)
A is a factor that depends on temp and dielectric constant of medium(0.51 for H2O),yi is activity coefficient, z is valence, u is ionic strength and can't be more than 0.02 |
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bronsted lowry theory of acids and bases
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acid is capable of donating proton, base is capable of accepting proton. solvent may be protophilic, protogenic, amphiprotic, or aprotic
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protophilic solvents
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acetone, ether, liquid ammonia
accepts protons |
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protogenic solvents
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formic acid, acetic acid, sulfuric acid, liquid HCl
donate protons |
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amphiprotic solvents
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water, alcohols
either accept or donate protons |
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aprotic solvents
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hydrocarbons
do not accept or donate protons |
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lewis electronic theory
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acid accepts electronic pair to form covalent bond, base provides electron pair
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arrhenius therory of acids and bases
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acid liberates hydrogen ions, base supply hydroxyl ions. only valid in aqueous media, only used for substances containing hydrogen
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law of mass action in ionization of weak acids
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rate of the forwad reaction is proportional to the concentration of the reactants
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weak acid ionization
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HAc= (c-x) H3O+=x Ac-=X
Ka=x^2/(c-x) or if c is large compared to x: Ka=x^2/c in general: ka=[H30+][B-]/[HB] |
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ionization of a weak base
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Kb=[OH-][BH+]/[B]
[OH-]=square root of (Kbc) |
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ionization of h2o
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kw=[H30+][OH-]
ionic product= 1 x 10^-14 at 25 C |
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sorensen's pH scale
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pH= -log[H3O+] and pOH= -log[OH-]
pKa + pKb= pKw, pH+pOH=pKw 0-14, 0-7 considered acidic and 7-14 basic |
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neutral pH at different temps
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7.0 at 25 C
7.47 at 0 C 6.15 at 100 C |
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buffers in blood
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maintain at 7.4, primary buffers in plasma-carbonic acid/bicarbonate and acid/alkali sodium salts of phosphoric acid
secondary buffers in erythrocytes-hemoglobin/oxyhemoglobin and acid/alkali potassium salts of phosphoric acid |
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henderson-hasselbalch equation
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pH=pKa+log[salt]/[acid]
or for a weak base: pH=pKw-pKb+log[base]/[salt] |
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buffer capacity
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quantitative measure of a buffers ability to neutralize externally added OH- or H+ ions. B= change in strong acid or base in gram equivalents per liter/ change in pH. larger capacity=greater ability to resist pH change
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adjusting tonicity
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class I methods-when osmotic pressure of solution is lower than body, sodium chloride is added to increase, amount measured by cryoscopic or sodium chloride equivalent method
class II- tonicity of solution is higher than body, add water calculated by white-vincent or sprowl's method |
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adsorption
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primarily a surface phenomenon, absorption occurs in bulk of solution.
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surface active molecules
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surfactants or amphiphiles-adsorbed at surfaces and interfaces and reduce surface tension,contain lipophilic and hydrophilic portions
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CMC
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critical micellar concentration-point at which surface is saturated with surfactant and the molecules begin entering the bulk, to minimize interfacial energy they orient into micelles
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micelles
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hydrophilic groups face the water and lipophilic face each other in a lipophilic core that can be used to solubilize lipophilic substances, diameter=50 A approx.
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properties affected by surfactants
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below CMC=surface and interfacial tension, vapor pressure
at or above CMC=density, conductivity, solubility of hydrophilic drugs affected |
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classification of surfactants
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HLB scale (hydrophile-lipophile balance) higher the HLB the more hydrophilic, surfactant charge is another way to classify
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HLB examples
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spans or sorbitan esters have low HLB values of 1.8 to 8.6, tweens or polyocyethylene derivatives of spans have high HLB values of 9.6 to 16.7
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anionic surfactants
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contain carboxylate, sulfonate, sulfate groups. ex. sodium stearate, sodium dodecyl sulfate, sodium lauryl sulfate
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cationic surfactants
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contain amine salts or quarternary ammonium salts. ex. cetrimonium bromide
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amphoteric surfactants
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contain carboxylate or phosphate groups as anion, and amino or quarternary ammonium groups as cation. carboxy/amine ex. polypeptides or proteins, phosph/ammonium ex. natural phospholipids like lecithins and cephalins
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non-ionic surfactants
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have no charge. ex. heptaoxyethylene
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uses of solid-gas adsorption and solid-liquid adsorption
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solid-gas: removal of odors from room or food, gas masks, measure of particles in powder
solid-liquid: decolorizing solutions, adsorption chromatography, detergency, wetting |
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solid-gas adsorption
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physical-van der waal's forces, reversible by desorption using increasing temp or decreasing pressure
chemical-irreversible, attachment of adsorbate to adsorbent by chemical bonds |
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measurement of physical adsorption
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measured by freundlich adsorption isotherms or langmuir adsorption isotherms
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freundlich adsorption isotherms
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balance within vacuum, degassed known amt of solid placed in pan, known amt gas introduced. x/m=kp^1/n x is amount gas adsorbed, p is partial pressure of gas, k and 1/n are empirical constants
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freundlich adsorption isotherms in log form
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log(x/m)=log k + 1/n(log p)
slope of straight line is 1/n and antilog of y-intercept is k |
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langmuir adsorption isotherms
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based on adsorption occuring as monolayer.
p/y= 1/bym + p/ym p is partial pressure, y is amt gas adsorbed per gram adsorbent, ym is amt gas 1g can adsorb for complete monolayer, b is constant |
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isotherm
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means constant temperature is assumed
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activated charcoal
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antidote by adsorption of sulfonlyureas like tolbutamide and acetohexamide, and acetaminophen and acetylcysteine. causes gastrointestinal dialysis by setting up conc. gradient that favors diffusion of drugs from systemic to gi tract
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wetting
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involves adsorption at solid-liquid interface, important in ensuring drug dissolution and absorption, greater contact angle=lower degree wetting=possible probs with dissolution and absorption
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interfacial tension
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tension at the interface of two immiscible liquids
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surface tension
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force per unit length (dynes/cm) that has to be applied parallel to the surface to counterbalance net inward pull
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capillary rise method for measuring surface tension
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capillary tube placed in water, water rises in tube to higher level than liquid surface due to adhesive forces of glass and liquid being greater than cohesive forces between liquid molecules. mercury is opposite
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capillary rise equation
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y=1/2(rhpg) y=surface tension r=inner radius of capillary tube h=height liquid rises to p=density of liquid g=acceleration due to gravity
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acceleration due to gravity
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981 cm/sec2
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dunouy ring method
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measure interfacial or surface tension with dunouy tensiometer. force to detach ring immersed at surface or interface is proportional to surface or interfacial tension
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methods for increasing solubility
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control pH, cosolvency, surfactants
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cosolvency
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a solute is more soluble in a mixture of solvents than one solvent, these solvents together are cosolvents.
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example of cosolvency
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1 g of phenobarbital is soluble in 1000ml water, 15 g of phenobarb is soluble in 22%alcohol, 40% glycerin and 38% water totaling 1000ml
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example of controlling pH to increase solubility
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1% solution of phenobarb soluble in alkaline solution, ppt out in pH below 8.3, conversely atropin sulphate is more soluble as pH is decreased into alkaline ranges
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partition coefficient
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substance added to a system of 2 immiscible liquids and reaches equilibrium it distributes in a ratio k=C1/C2, where C1 and C2 are equilibrium conc. of the 2 solvents. applicable only in dilute sol. where activity coefficients can be neglected
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importance of partition coefficient in pharmacy
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preservation of oil-water systems, drug action in non-specific sites, absorption and distribution of drugs throughout body
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diffusion
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process of mass transfer brought about by random brownian motion of particles
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fick's 1st law of diffusion
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flux is proportional to the concentration gradient. J= -D(dC/dx) D is diffusion coefficient, x is distance in cm of movement perp. to barrier
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flux
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amount of material M flowing through a unit cross section S of a barrier in unit time T J=dM/S x dt
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fick's 2nd law of diffusion
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determine rate of change of conc. relative to position in system. dC/dt = D(d^2C/dx^2)
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diffusion apparatus
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diffusion cells consisting of 2 chambers (donor and receiver) separated by membrane. amt of drug that penetrates into receiver chamber is measured as function of time.
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lag time
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tl=h^2/6D
h is thickness of membrane |
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noyes and whitney equation
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rate at which solid dissolves in a solvent dC/dt=(DS/Vh)(Cs-C) C is conc. of solute in bulk at time t, D is diffusion coefficient, S is surface area of exposed solid, h is thickness of diffusion layer, CS is solubility of solid, V is volume of solution
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percutaneous absorption
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process of mass movement of substances from surface of skin into systemic circulation
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factors involved in percutaneous absorption
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dissolution of drug in vehicle, diffusion of drug from vehicle to surface of skin, movement of drug from surface of skin to systemic circulation
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factors affecting percutaneous drug absorption
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drug concentration, skin/drug/vehicle interactions, drug solubility and molecular weight, vehicles/solvents, physiological condition of the skin
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why measure percutaneous absorption?
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to estimate dermatotoxicity and in dermatopharmacology, can be measured in vivo or in vitro
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measuring percutaneous absorption in vitro
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horizontal diffusion cell, donor chamber with skin mounted between it and receptor chamber containing buffer to simulate physiological conditions
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most common receptor medium for measuring percutaneous absorption
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PBS-phosphate buffered saline with pH of 7.4
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permeability coefficient
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Kp= - jss/Cv jss is steady state flux, absorption rate per unit area
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enhancement of percutaneous penetration by chemical methods
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ethanol, propylene glycol,oleic acid,dimethyl sulfoxide,azone alter barrier property of stratum corneum
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enhancement of percutaneous penetration by physical methods
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iontophoresis, electroporation, phonophoresis
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iontophoresis
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application of mild electrical current to increase migration of ions and charged molecules through skin. might affect morphology of skin
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electroporation
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application of high voltage electric pulses of short duration, reversibly create tiny pores that allow large molecules to pass
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phonophoresis
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aka sonophoresis-movement of drugs under influence of ultrasound (beyond 20kHz) alters lipid structure of stratum corneum to improve permeability
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methods to evaluate biophysical properties of skin
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DSC-differential scanning calorimetry, 4 transitions 25-105 for stratum corneum
FT-IR-fourier transform infrared spectroscopy, peaks near 2850 and 2920 due to C-H stretch(symmetric for first, asymmetric for second), amide absorbance 1500-1700 due to C=O stretch and N-H bend in lipid and protein |
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TEWL
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transepidermal water loss-increases with perturbation of skin, measured using evaporimeter
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skin capacitance
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measure of water content in stratum corneum using corneometer
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acute uraemias influence on NSAID absorption
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increase in BUN is sign of renal failure, urea precipitates on skin, increased conc. in skin, mild keratolytic effect, loosening stratum corneum. percutaneous absorption decreased significantly in uremic rats
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topical corticosteroids absorption
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inflammation/disease process in skin increases absorption, occlusive dressings increase absorption
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metrology
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science of weights and measures
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balance types
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single beam equal arm balances, unequal arm balances, compound lever balances, torsion balances (prescription balances are these)
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max maintenance sensitivity for class III balances
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6 mg (amount to cause indicator to shift not less than one division)
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minimum weighable quantity
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MWQ=sensitivity/error
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rheology
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science that studies flow of liquids and deformation of solids
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viscosity
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resistance offered by a liquid or a fluid to flow. higher viscosity=more resistance. denoted by n
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fluidity
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ease with which a liquid or a fluid flows, reciprocal of viscosity sigma=1/n
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newtonian liquids
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velocity of flow is a function of distance, force applied per unit area (shearing stress, F) is proportional to rate of shear F=nG, G is velocity gradient, n is coefficient of viscosity, plot of F vs. G is straight line passing through origin
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viscosity units
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poise, cgs are g/cmsec
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kinematic viscosity
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n/p viscosity divided by density at constant temp
units are stokes |
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arrhenius equation for the dependence of viscosity on temp
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n=Ae^Ev/RT
A is a constant depending on molecular weight and molar volume Ev is activation energy to initiate flow |
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Non Newtonian liquids
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colloidal solutions, emulsions, liquid suspensions, ointments, etc make up this class. 3 main types:plastic flow,pseudoplastic flow, dilatant flow
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plastic flow
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does not flow until applied shearing stress exceeds yield value, below which it acts as elastic solid, above as newtonian liquid. ex. concentrated suspensions
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pseudoplastic flow
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flows more readily with increased, thinner on application of stress, polymers in solution are example. no yield value.
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dilatant flow
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opposite pseudoplastic, liquid becomes thicker, flow with increased resistance with app. of stress. ex. conc. suspensions
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thixotropic
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special characteristic exhibited by shear thinning systems such as pseudoplastic and plastic. remain in thinned state after shear is removed, for an extended period of time. "isothermal and comparatively slow recovery, of a consistency lost through shearing"
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thixotropic in pharmacy
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useful to avoid settling of drug particles in suspension, shaking will thin suspension and it will remain thin long enough to pour and dispense
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measurement of viscosity
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viscometry: operate at a single rate of shear. ex. capillary viscometers such as ostwald for liquids that flow easily.
operate at multiple rates of shear ex. cup and bob and cone and plate, useful for nonnewtonian and semi-solids like gels and pastes |
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blood
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a fluidized suspension of elastic cells, both viscous and elastic determine stress-to-strain rate relationship, called visoelastic. blood plasma is only viscous, whole blood is viscous and elastic
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origin of blood visoelasticity
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traceable to elastic rbc's which occupy 1/2 its volume. aggregation and deformability of rbc's are key factors
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red blood cell aggregates
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size diminishes as shear rate increases
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increasing shear rate in blood
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deforms cells so they form layers that slide on layers of plasma. cells w/impaired deformability produce dilatant viscoelasticity marked by elevated viscosity and elasticity when under high shear
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examples of things that effect blood viscoelasticity
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changes in osmotic pressure, pH, concentration of fibrinogen and other plasma proteins, clinically introduced blood volume expanders
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blood change in cardiopulmonary bypass surgery
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plasma viscosity, effects of priming solution on aggregation, deformability of rbc's, and dilution of plasma proteins
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polymers
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macromolecules-repeating units of small chemical compounds called monomers, 10's, 100's, 1000's
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examples of polymers
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proteins-from amino acids
DNA-from nucleotides starches, cellulose-from sugars |
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pharmaceutical uses of polymers
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thickening agents,coating solid dosage forms, miscellaneous tablet excipients, sustained release dosage forms, drugs, packaging drugs and dosage forms
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thickening agents
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polymers in water can result in increased viscosity. methyl cellulose, gums like acacia and tragacanth. improve stability of emulsions and suspensions
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coating solid dosage forms
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polymers such as sugars are used to coat tablets and mask the taste. enteric coating by a polymer to enable dissolution only in intestine. ex. cellulose acetate phthalate, hydroxypropyl methylcellulose phthalate, copolymers of methacrylic acid and its esters
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miscellaneous tablet excipients
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polymers such as acacia, gelatin, sodium alginate are used as binders for tableting granulations. others like starch are used as tablet disintegrants
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sustained release dosage forms
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numerous synthetic polymers like polyactic glycolic acids (PLGAs), polyanhydrides, polycaprolactones, celluloses used to design sustained release oral and parentral
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polymers as drugs
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insulin,heparin,protamine sulfate,plasma volume expanders like dextran and human albumin, laxatives like methyl cellulose
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polymers in packaging
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polyolefin bottles,polystyrene vials, rubber closures
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physical properties of polymers
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molecular weight is most important, it is difficult to manufacture w/precise weight, molecular weight distribution is therefore important for pharmaceutical polymers
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determining molecular weight of polymers
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solution viscosity and laser light scattering
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solubility of polymers
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rate of dissolution is very important because they dissolve slowly due to large size. occurs in 2 phases: gel formation and disentanglement of polymer in gel
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disentanglement of polymer molecules from gel
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once the initial gel has formed the swollen polymer molecules gradually start disentangling from the gel structure to dissolve in solvent
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methyl cellulose solubility
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more soluble in cold water than hot, begin by mixing in hot water and applying high shear, now add cold water to slowly cool and dissolve, similar process for hydroxypropyl cellulose and hydroxypropyl methyl cellulose
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melting point of polymers
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excluding biological polymers like proteins and DNA, polymers don't have distinct melting points, melt over broad range
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polymers as crystals
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many polymers exhibit partial crystallinity.
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