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Ceutics Exam 2
PHARMACY SCHOOL--exam 2
| Question | Answer |
|---|---|
| buffer solution | solution that is able to resist a significant change in its pH on the addition of limited amounts of an acid or a base or on dilution with solvent |
| from a pharmaceutical perspective, why is it important to control the pH of a solution? | minimize drug degradation, improve patient comfort and compliance, and improve the solubility and/or efficacy of a delivery |
| how do we calculate pH | henderson Haselbach equation pH=pKa + log (I/U) (for weak acid) |
| buffer capacity | aka: buffer effect/buffer value; the protective strength of the buffer (every buffer will reach a point where it no longer can protect the preparation from added acids and/or bases) |
| how to calculate buffer capacity? | van slyke equation |
| two components of a buffered solution | weak acid and its conjugate base(soluble salt of the acid) |
| CH3COOH +H2O <--> H3O+ + CH3COO- what happens if you add extra H3O+? | -pushes equation to the left |
| weak bases as buffers | not commonly used as they are unstable, volatile, and dependent on temperature |
| characteristics of a buffer solution | pH and buffer capacity |
| what is the pH of a buffer solution containing phenobarbital and its sodium salt if the molar concentration of phenobarbital is 0.03 M and that of sodium phenobarbital is 0.02 M. the pKa for phenobarbital is 7.4 | answer=7.2 |
| pH depends on? | the ratio of salt to acid!! (see example of this in notebook on page that says flashcard explanation) |
| symbols for: activity, activity coefficient, and ionic strength | a(alpha), y (lambda), u(nu) |
| effective concentration vs actual concentration | in conc. solutions effective conc. of ions in soln. is lower than actual conc. bc electrostatic attraction and ion assoc. In an ion pair, the cation and anion are in intimate contact in soln. and migrate as single unit (not completely dissoc.) |
| so effective concentration of the ion is called? | activity (a (alpha)) of the ion. |
| equation to calculate activity of the ion | a (alpha)= y(lambda) x C units of a= moles/L units of y= no units..activity coefficient units of C= moles/L |
| what is an ideal solution? | solutions whose colligative properties are proportional to the concentration of the solute |
| in ideal solutions and in dilute solutions ionic interactions can be ignored.... | and activity coefficient (y) approaches unity (1) and concentration is equal to activity.....a=C |
| as y(activity coefficient) gets larger... as activity coefficient gets smaller.... | the solution is more dilute the solution is more concentrated |
| so what is activity coefficient (y) | it corrects for electrostatic shielding by other ions (the charge on the ions that attracts or repels other ionic species as well as polar species) |
| so y depends on? | the ionic strength of the solution (which is a function of the concentration of ions in the solution)....the higher the concentration the lower the activity coefficient) |
| what is ionic strength of a solution | a measure of the concentration of all ions present in that solution |
| formula for ionic concentration | u=.5∑cz^2 u: ionic strength of solution c: molar concentration of the ion z:valence (charge) of the ion (neglecting it's sign) |
| What is the ionic strength of a 0.010 M sodium sulfate (Na2SO4-) | answer: 0.030 M (see ceutics exam 2 notes for work) |
| what equation shows the relationship between activity coefficient (y) and ionic strength (u)? | debye-huckel equation: log y = -Kz^2 sq.rt. u see looseleaf ceutics exam 2 notes for better written out equation. |
| K in debye huckle equation is? | constant. in water at 25 degrees C it is 0,51 |
| z in debye huckle is? | valence (charge) of the ion (neglecting its sign) |
| u in debye huckle is? | ionic strength of solution |
| as activity coefficient increases the ionic strength? | decreases |
| as y approaches unity (1) then ionic strength (u) approaches? | zero |
| a solution contains 0.001 M NaCl and 0.003 M CaCl2. Calculate (a) the ionic strength of this solution and (b) the activity of sodium ion in the solution if the K value at the specified temperature is 0.51. | a: 0.028 b: 0.0008216 M for work see looseleaf ceutics exam 2 notes) |
| equation that is useful for calculating the pH of a weak acid in water if one knows the molar concentration (C) and the pKa of the weak acid.....solution containing weak acid only | pH= .5 pKa - .5 log C |
| what is the pH of a 0.1M solution of weak acid? pKa of the acid is 4.76. | answer=2.88 for work see ceutics exam 2 notes (looseleaf) |
| equation useful for calculating the pH of a weak acid in water if one knows the molar concentration (C) and the pKa of the weak base.....solution containing weak base only | pH=.5pKw +.5pKa+ .5log C |
| how do you calculate pH from pOH? | pKw-pOH=pH pKw is 14 |
| what is the pH of a 0.1M solution of a weak base trimethylamine (pKb 4.28) at 25 degrees C (77 degrees F)? | answer=11.36 for work see ceutics exam 2 notes (looseleaf) |
| buffer capacity...symbol and definition | B; the ratio of the amount of base or acid (ΔB) in gram equivalents/liter (molar) that needs to be added to the buffer solution to produce a particular change in pH (ΔpH) |
| buffer capacity equation | B=ΔB/ΔpH |
| in the addition of 0.1 mole of HCl (molecular weight =36.5 g/mole) to 1 L of a buffer solution caused a drop in the pH by 0.4 unit, what is buffer capacity? | answer is 0.25 (see ceutics exam 2 notes on looseleaf for work) |
| for the rest of acid/base chemistry part B powerpoint see the example problems on your ceutics exam 2 looseleaf paper | |
| what does it mean to say sugar is soluble in water? | sugar crystals break apart in solution (it's a molecular dispersion=solution) |
| solubility limit aka | solubility (how much solute will go into solution) |
| why is solubility important to pharmacists? | it governs the preparation of solutions as a dosage form and a drug must be in solution before it can be absorbed by the body to exert biology activity |
| why must a drug be in solution before it can be absorbed by the body? | because the soluble form has ability to cross in intestine and enter bloodstream |
| so how do we make solution or something that can be dissolved in the body? | adjust pH of weak acid to increase ionization which will increase solubility |
| define solubility | solubility of a substance at a given temperature is defined as the quantity of a particular substance (solute) that can dissolve in a particular solvent (yielding a saturated solution) |
| so solubility is ____________ dependent | temperature (it can increase or decrease solubility when temp is increased or decreased....raising temp does not always increase temp) |
| solubility as a number is | the concentration of dissolved solute when it is in equilibrium with the undissolved solute |
| room temperature is | 23 degrees C (approximately) |
| solubility of sucrose (table sugar) in water at room temperature | 2.0 g/mL |
| so what would happen in this particular case (sucrose in water) if you increased temperature | here it happens to cause more to go into solution...but remember increasing temp. does not always increase solubility |
| miscibility | used to refer to the solute when it is in a liquid and will form a solution with solvent over any concentration range, i.e. liquid-liquid systems |
| saturated solution | solution that contains undissolved solid solute where the rate at which the molecules or ions leave the solid solute surface is equal to the rate at which the dissolved molecules return to the solid and the system is in equilibrium |
| unsaturated solution | solution that contains the dissolved solute in a concentration lower than that of saturated solution |
| supersaturated solution | solution that contains a higher concentration of the dissolved solute than that at the dissolution equilibrium |
| which type of solution are most pharmaceutical solutions | unsaturated |
| how can a supersaturated solution of sucrose be achieved? | lower the temperature and the sugar will precipitate out |
| three ways to adjust solubility? | temperature, pH, and salts |
| percent weight | gram of solute/ 100g of solution |
| percent volume | milliliters of solute/100 mL of solution |
| percent weight/volume | gram of solute/100 mL of solution |
| normality | gram equivalent weights of solute/liter of solution |
| molarity | moles of solute/liter of solution |
| molality | moles of solute/1000g of solvent |
| mole fraction | ratio of the moles of one component (the solute) of a solution to the total moles of all components (solute and solvent) |
| milliequivalent per liter | milligram equivalent weights (equivalent weight express in mg, mEq of solute/liter of solution) |
| osmolarity | osmoles of solute/liter of solution |
| osmolality | osmoles of solute/1000g of solvent |
| what is the percent w/v of NF simple syrup | 85% (85g/100ml) |
| so now what is the % w/w if we know specific gravity is 1.313? | 65% |
| how to calculate grams given your mL and sp. gr | mL (sp. gr.)= grams |
| terms of solubility (mandated by USP) | very soluble, freely soluble, soluble, sparingly soluble, slightly soluble, very slightly soluble, practically insoluble or insoluble |
| very soluble | less than 1 part of solvent required to dissolve one part of solute |
| freely soluble | 1-10 parts of solvent required to dissolve one part of solute |
| soluble | 10-30 parts of solvent required to dissolve one part of solute |
| sparingly soluble | 30-100 parts of solvent required to dissolve one part of solute |
| slightly soluble | 100-1000 parts of solvent required to dissolve one part of solute |
| very slightly soluble | 1000-10,000 parts of solvent required to dissolve one part of solute |
| practically insoluble or insoluble | greater than or equal to 10,000 parts of solvent required to dissolve one part of solute |
| so what is the term of solubility used to describe sucrose? | sugar is 2g/ml so that means for one part of sugar to be dissolved 0.5 parts of solvent are required...which is less than one so it is very soluble |
| intrinsic solubility | maximum concentration to which a solution can be prepared with a specific solute in the UNIONIZED form and solvent at a specific temperature |
| apparent (total) solubility | the sum of the concentrations of the ionized form and the unionized form in a saturated solution |
| equation that relates intrinsic and apparent solubilities | S= So + Si see example on slide 14 S=apparent total solubility So=solubility (or the concentration) of the unionized form of the compound in its saturated solution Si= the concentration of the ionized form of the compound (A- or B+) |
| in a saturated solution the solubility of the unionized form of the weak acid is equal to? | So |
| in a saturated solution the concentration of the ionized form of the weak acid or weak base is equal to | Si or (S-So) |
| So HA in the equation is | unionized (So) |
| and A- is what in the equation? | ionized (Si) |
| apparent total solubility of weak acids | S=So(1+(Ka/H+))...see how derived on page 8 bottom slide solubility part 1 |
| apparent total solubility of weak bases | S= So(1+ (H+/Ka))...see how derived on page 9 top slide solubility part 1 |
| difference in henderson hasslebach and apparent total solubility | henderson Haselbach is not at saturation. can calculate pH of precipitation from solubility equation but NOT H-H |
| pH of precipitation | the limit of pH beyond which precipitation will occur...precipitation occurs at pH values lower than this limit for weak acids but at pH values above this limit for weak bases |
| pH of precipitation equation for weak acid | pHp= pKa+ log ((S-So)/So) |
| pH of precipitation equation for weak base | pHp= pKa+log (So/(S-So)) |
| see two practice problems on your looseleaf ceutics exam 2 notes | |
| dissolution | the process by which molecules leave the solid phase and enter solution |
| dissolution in water is called | hydration |
| process of dissolution includes two molecular events: | the transfer of solute molecules from the solid phase to the liquid phase and the transfer of the dissolved solute molecules back to the solid phase from the liquid phase |
| so process of dissolution involves | 1-breaking of INTERMOLECULAR bonds in the solute 2-separation of molecules of the solvent to provide a hole in solvent for solute molecule 3-interaction b/w solvent and solvent molecules |
| net result of the molecular interactions as the solute dissolves is manifested energetically as? | heat of solution (delta Hsol) |
| heat of solution is aka | enthalpy of solution or enthalpy of dissolution |
| equation that established a quantitative description for dissolution | Noyes and Whitney |
| what is the Noyes and Whitney equation? | dM/dt= DA/h(Cs-Ct) dM/dt=rate of dissolution D diffusion coefficient in th diffusion layer h=thickness of diffusion layer A=surface area of drug particles Cs=saturation conc. of drug in diffusion layer Ct=conc. of drug in bulk fluids at time t |
| so what constitutes a concentration gradient | the conc. difference of solute between drug in diffusion layer and drug in bulk fluids. keep Ct low to create driving force and increase rate |
| ways to force something into dissolution | keep Ct low by filtering liquid out and adding fresh liquid, stirring disrupts saturated layer making it smaller to increase rate, increase surface area by triturating drug |
| diffusion coefficient (D) is expressed by what equation? | Stokes-Einstein equation....D=kT/6 pi n r k=boltzmann constant (1.3807 x 10^-23 JK^-1) T=temp in kelvin (degrees C plus 273) r=size (molecular weight) of molecule n=viscosity |
| so decrease size of molecule what happens to rate | increase rate |
| so increase viscosity what happens to rate | decrease rate |
| sink condition | volume of the medium is at least three times greater than that needed to form a saturated solution of a drug substance |
| equation written how under sink condition | dM/dt= kACs |
| factors affecting solubility | 1. chemical and physical properties of the solute 2. presence of co-solvent (condition of the solution) 3. temperature (condition of the solution) 4. the pH of solution (condition of the solution) |
| what is the general rule for chemical and physical properties of the solute | like dissolves like (the greater the similarity between the solute and the solvent (physical-chemical properties) the greater the solubility |
| chemical and physical properties of the solute | nature of the solute (chemistry), chain length, branching, polarity, h-bonding, and steric factor, solute crystal structure |
| nature of solute | can be organic or inorganic |
| virtually all drugs on the market are which type of solute | organic compounds |
| most organic compounds are more or _______ polar and hence dissolve _____ in organic solvents than water | less; better |
| inorganic compounds in general have high or low polarity and hence are more or less soluble in water | high, more |
| most inorganic compounds form what? and how? | crystals by strong ionic interactions |
| dissolution of an ionic compound relies on? | the strong ion-dipole interactions between the ions of the crystal and water molecules to overcome such solute-solute attraction forces |
| compounds are generally water soluble if both the cation and anion are? | monovalent (NaCl, KOH) exceptions are silver and mercury salts |
| compounds are also generally water soluble if one of the two ions is | monovalent (BaCl3, Na3PO4, Na2SO4) exceptions are hydroxides |
| compounds are generally poorly water soluble when | the cation and anion are both multivalent (CaSO4, ZnSO4, BaSO4) |
| strong organic electrolytes and their solubility | strong acids, strong bases, and salts of organic compounds are soluble in water |
| example of strong organic electrolyte | benzenesulfonic acid |
| weak electrolytes and their solubility | weak acids & weak bases with high molecular weight are poorly soluble in water |
| what if you use ionized for of a weak acid or weak base? | then solubility is strong |
| non electrolytes and their solubility | high molecular weight organic drugs that do not dissociate in water are generally soluble in organic solvents and have little or no solubility in water |
| general rule for chain length and solubility | solubility in water decreases with an increase in number of carbon atoms in the solute...water solubility decreases with increases in molecular weight |
| so methanol solubility vs decanol solubility | methanol is very soluble and decanol is insoluble in water...so the larger molecule is not as soluble |
| branching is also known as | steric factor |
| general rule regarding branching and solubility | the more branched hydrophobic carbon change leads to higher water solubility compared to the corresponding straight chain compounds |
| explain why solubility for branching and non branching is the way it is | the straight chains can stack nicely and form induced dipole bond but if you introduce branching they don't stack nicely anymore and water can dissolve them |
| role of polarity in solubility | molecules that have a high dipole moment are more soluble in polar solvents such as water |
| role of hydrogen bonding in solubility | solubility inc. with inc. in capacity of solute to form H-bonds(OH, NH, and SH containing compounds), as number of OH groups inc. it's solubility in water often increases and as ratio of OH groups to # of C atoms increases solubility in water inc. |
| is glucose water soluble? | highly water soluble bc of high number of OH groups it has that allow it to H-bond with water...but it's a non electrolyte so it's an exception to the non-electrolyte rule |
| see slide at top of page nine of solubility part two packet to rank solubility of the listed compounds | |
| solute crystal structure is what | the solid-state chemistry of drugs...ordered arrangement of molecules over a long range |
| what is a small molecule | low molecular weight (<900 daltons) compounds. most drugs are small molecules |
| macromolecules | polymers (won't discuss much until ceutics 2...proteins, carbohydrates, etc) |
| organic and inorganic small molecules can arrange in what two general ways | 1. ordered repeating 3D structure called crystal lattice, thus producing a crystalline solid 2. aggregate w/ no particular order in which they form amorphous (shapeless)solid |
| crystals (lattice or crystal lattice) | solids where all atoms, molecules, or ions are the same distance from the same # and type of neighbors. so the intermolecular forces holding the solid together are uniform, & same amt. of thermal energy is needed to break every interaction simultaneously |
| melting points of crystals | have relatively sharp, well-defined melting points...takes lots of energy to make the bonds |
| so distance and angles of molecules in crystal lattice | molecules same distance apart with same angles between them |
| amorphous melting point | no sharp melting point because of random arrangement, not uniform |
| most drugs are crystalline or amorphous | crystalline |
| how are crystals held together | intermolecular forces |
| the arrangement of molecules in a crystal determine what? | its physical properties |
| so if you make the bonds longer between molecules in a crystal then? | lower MP, and other physical properties such as BP and solubility will change too |
| the shape and size of the crystal which is related to its internal crystal structure can influence what? | its bulk properties |
| bulk properties are | flowability, syringe ability, filterability, tableting behavior, and bulk density |
| which is easier to inject: a suspension containing a drug in crystal form with platelet like crystals or need-like crystals | platelet like crystals are easier to get through a fine needle than need-like crystals. |
| crystal habit | external appearance of a crystal |
| types of crystal habits | prismatic, bladed, equant or massive, tabular cubic |
| does the crystal habit give you a clue about what the arrangement of the inside of the crystal is like? | no it does not |
| morphology | this term merely acknowledges the fact of different shapes and does not distinguish among the many possible reasons for the different shapes (more work is needed to det. whether the diff. shapes are indicative of polymorphs, solvates, or just habits) |
| can crystals have the same chemical composition and same crystal structure but different habits? | yes they can have the same polymorph and unit cell but display different shapes |
| crystal, lattice or crystal lattice | a solid that consists of repeating unit cells (lattice units) |
| unit cells | the smallest identical units that, when stacked together, form the crystal |
| how many common lattice units | seven |
| what are the common lattice units | cubic, tetragonal, orthorhombic, monoclinic, hexagonal, rhombohedral, triclinic (see pictures on top of p 15 of solubility part 2 slides) |
| how are lattice units defined | length (a,b,c) and angles (alpha, beta, gamma) of the lattice |
| all unit cells in a specific crystal are | same size and contain same number of molecules or ions arranged in the same way |
| polymorphism | ability of any element or compound and its ability to crystallize as more than one distinct crystal species (unit cell structure) |
| polymorphs | the different crystal arrangements o the same chemical composition (sometimes used more broadly to include both the amorphous state and solvates) |
| so what does polymorphism depend on? | storage conditions. humidity can give a lot of energy and allow molecules to move around which can cause molecules to shift crystal form even tho it's same drug. so it can transition to one form to another. poses issues if it changes to less soluble form |
| solvates | compounds where solvent molecules are incorporated in the crystal lattice |
| solvates sometimes called | pseudopolymorphs |
| hydrates | compounds where water is the solvent of crystallization |
| hydrates and solvates exist as | different polymorphs |
| monohydrate | contains one water molecule per drug molecule |
| dihydrate | contains two water molecules per drug molecule |
| anhydrates | crystals that contain no water of crystallization are termed anhydrides. anhydrous crystals usually have higher aqueous solubility than hydrates |
| different polymorphs will have | different free energies and therefore different physical properties such as solubility, chemical stability, mp, and density |
| if the change from one polymorph to another is reversible the process is | enantiotropic |
| if the transition from metastable (less stable) to a stable polymorph is unidirectional the system is | monotropic |
| what's the problem with the more stable form? | it's less soluble...so we need less stable but when you do this you risk the transition to the stable form |
| amorphous solids | solid materials that lack the 3D long-range order characteristics of a crystal. these solids are referred to as glasses |
| does crystalline or amorphous form have higher mp and bp | crystalline bc it takes more energy to break these bonds than amorphous |
| amorphous solid melting point | these tend to soften slowly over a wide temperature range rather than having a well defined mp like a crystalline solid..they are instead defined by a glass transition (Tg) temperature |
| Tg temperature | temp. when an amorphous material converts from a glass to a supercooled liquid upon heating. When T>Tg the rigid solid can flow & corresponding inc. in molecular mobility can result in crystallization or inc. chemical reactivity of the solid |
| if amorphous solid is maintained at a temp just below its mp for long periods of time under certain conditions such as high humidity and heat... | the component molecules, atoms, or ions can gradually rearrange into a more highly ordered crystalline form |
| amorphous solids are usually more or less soluble than their crystalline counterparts | more because there is no crystal lattice that needs to be broken before the material can dissolve |
| make sure to review last two powerpoint slides for this exam...solubility part 3 and milliequivalants. |
Created by:
SarahESpano