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PHYSICAL PHARMACEUTICS- I (BP302T), Exercises of Pharmacy

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IMPORTANT QUESTIONS WITH ANSWERS
PHYSICAL PHARMACEUTICS- I (BP302T)
UNIT-I
Q.1 State Raoult’s law. What do you understand by ideal and real solution?
Answer:
RAOULT’S LAW
“The partial pressure of each component in a solution is directly proportional to the vapour pressure of
the corresponding pure substance and that the proportionality constant is the mole fraction of the
component in the liquid.”
For a binary solution having volatile components A and B:
PA0 α PA and PB0 α PB
Then, PA0 = PAXA and PB0 = PBXB
where, PA0= partial pressure of A, PB0 = partial pressure of B
PA= vapour pressure of A, PB=vapour pressure of B
XA= mole fraction of A, XB= mole fraction of B
IDEAL AND NON-IDEAL SOLUTIONS
Ideal solutions
Definition: solution which obeys
Raoult’s law over the entire range of
concentration and temperature and during
the formation of which no change in
enthalpy and no change in volume takes
place.
Non-ideal solutions
Definition: The solutions which do not obey Raoult’s law and are
accompanied by change in enthalpy and change in volume during their
formation are called non-ideal solutions.
Solutions with positive
deviations
Solutions with negative
deviations
A……B interactions are similar to
A……A and B……B interactions
A……B interactions are smaller
than A……A and B……B
interactions
A……B interactions are greater
than A……A and B……B
interactions
PA0 = PAXA and PB0 = PBXB .
PA0 > PAXA and PB0 >PBXB .
PA0 < PAXA and PB0 < PBXB .
Hsolution = 0
Hsolution> 0
Hsolution< 0
Vmixing = 0
Vmixing> 0
Vmixing< 0
Do not form azeotrope
form minimum boiling point
azeotrope
form maximum boiling azeotrope
Examples: Chlorobenzene and
bromobenzene, Benzene and toluene
Examples: ethanol and water,
methanol and water
Examples: acetic acid and
pyridine, HCl and water
Q.2 Explain ideal solubility parameters. What are its applications, advantages and limitations?
Answer:
IDEAL SOLUBILITY PARAMETERS:
To estimate solubility as a result of solute- solvent interactions, some ideal solubility parameters are
required, which are very well explained by “Regular Solution Theory”. This theory suggests a
numerical estimation about solubility-
δ1 = ( ΔU/V )1/2 = [(ΔH-RT) / V]1/2
where, δ1 = solubility parameter
ΔU = molar energy, V = molar volume of solvent, ΔU/V = cohesive energy density of solvent
ΔH = molar heat of vaporisation of solvent, R = gas constant, T = temperature
The difference between δ1 and δ2 1 - δ2) gives the numerical value for solubility.
Unit of solubility parameters:
1). Conventional- (Cal/ cm3)1/2 or Cal1/2cm-3/2
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pf4
pf5
pf8
pf9
pfa
pfd
pfe
pff
pf12
pf13
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IMPORTANT QUESTIONS WITH ANSWERS

PHYSICAL PHARMACEUTICS- I (BP302T)

UNIT-I

Q.1 State Raoult’s law. What do you understand by ideal and real solution? Answer: RAOULT’S LAW

- “The partial pressure of each component in a solution is directly proportional to the vapour pressure of the corresponding pure substance and that the proportionality constant is the mole fraction of the component in the liquid.” - For a binary solution having volatile components A and B: PA^0 α PA and PB^0 α PB Then, PA^0 = PAXA and PB^0 = PBXB where, PA^0 = partial pressure of A, PB^0 = partial pressure of B PA= vapour pressure of A, PB=vapour pressure of B XA= mole fraction of A, XB= mole fraction of B IDEAL AND NON-IDEAL SOLUTIONS Ideal solutions Definition: solution which obeys Raoult’s law over the entire range of concentration and temperature and during the formation of which no change in enthalpy and no change in volume takes place. Non-ideal solutions Definition: The solutions which do not obey Raoult’s law and are accompanied by change in enthalpy and change in volume during their formation are called non-ideal solutions. Solutions with positive deviations Solutions with negative deviations A …… B interactions are similar to A …… A and B …… B interactions A …… B interactions are smaller than A …… A and B …… B interactions A …… B interactions are greater than A …… A and B …… B interactions PA^0 = PAXA and PB^0 = PBXB. PA^0 > PAXA and PB^0 >PBXB. PA^0 < PAXA and PB^0 < PBXB. Hsolution = 0 Hsolution> 0 Hsolution< 0 Vmixing = 0 Vmixing> 0 Vmixing< 0 Do not form azeotrope form minimum boiling point azeotrope form maximum boiling azeotrope Examples: Chlorobenzene and bromobenzene, Benzene and toluene Examples: ethanol and water, methanol and water Examples: acetic acid and pyridine, HCl and water Q.2 Explain ideal solubility parameters. What are its applications, advantages and limitations? Answer: IDEAL SOLUBILITY PARAMETERS:

  • To estimate solubility as a result of solute- solvent interactions, some ideal solubility parameters are required, which are very well explained by “Regular Solution Theory”. This theory suggests a numerical estimation about solubility- δ 1 = ( ΔU/V )1/2^ = [(ΔH-RT) / V]1/ where, δ 1 = solubility parameter ΔU = molar energy, V = molar volume of solvent, ΔU/V = cohesive energy density of solvent ΔH = molar heat of vaporisation of solvent, R = gas constant, T = temperature
  • The difference between δ 1 and δ 2 (δ 1 - δ 2 ) gives the numerical value for solubility.
  • Unit of solubility parameters: 1). Conventional- (Cal/ cm^3 )1/2^ or Cal1/2cm-3/

2). SI unit- J1/2m-3/2^ i.e. equivalent to Pa1/

  • Applications of solubility parameters:
    1. Selection of solvent.
    2. Preparation of polarity scales.
    3. Cosolvancy power determination.
    4. Chemical kinetics determination.
    5. Determination of mechanism involved in drug action.
    6. Structural activity relationship (SAR).
    7. Drug transport through model membranes.
  • Advantages of Regular Solution Theory: to predict excess free energy of mixing.
  • Limitation of Regular Solution Theory: not able to predict thermodynamic properties like- a) heat of salvation, b) volume after mixing. Q.3 Define solubility. Explain mechanism of solute- solvent interaction. Mention the reason of solubility in different type of solvents. Answer: SOLUBILITY:
  • in a quantitative way: it is the concentration of solute in a saturated solution at a certain temperature.
  • in a qualitative way: it is the spontaneous interaction of two or more substances (solute & solvent) to form a homogeneous molecular dispersion. MECHANISMS OF SOLUTE-SOLVENT INTERACTIONS:
  • When solute gets dissolved in solvent? Solute - solute interaction < Solute - solvent interaction > solvent - solvent interaction.
  • When favourable interaction takes place between solute and solvent then solute gets dissolved in solvent.
  • This dissolving process depends on free energy change of solute and solvent.
  • Mechanism involves 3 steps:-
  1. Detachement of solute from bulk form.
    Solute bulk (Solute bulk – 1) Detached solute molecule
  • Enthelpically unfavourable, Entropically favourable.
  1. Formation of vacant site in solvent. Vacant site + Solvent Solvent with vacant site Free solvent molecule
  • Enthelpically and Entropically favourable.
  1. Insertion of detached solute molecule in vacant site of solvent.
    • Solvent with embedded solute molecule
  • Entropically favourable. **REASONS OF SOLUTE – SOLVENT INTERACTION IN DIFFERENT SOLVENTS:
  1. Polar solvents:** a) Dielectric constant: due to their high dielectric constant, polar solvents reduce the force of attraction between oppositely charged ions in crystals. Example : water possessing a high dielectric constant (≥ 80) can dissolve NaCl, while chloroform (≥5) & benzene (≥2) cannot. Ionic compounds are practically insoluble in these 2 solvents. b) Hydrogen bond formation c) Ability of breaking covalent bonds CH 3 COOH + NaOH CH 3 COONa + H 2 O 2. Non polar solvents:

SYSTEMS WITH NO CST:

  • Example: ethyl ether and water, has neither an upper nor a lower CST
  • shows partial miscibility over the entire temperature range at which the mixture exists. Q.5 State the various expressions used for expressing the solubility. Discuss distribution law. Answer: SOLUBILITY EXPRESSIONS: a) Quantitative expressions: Expression Symbol Definition Molarity M, c Moles of solute in 1 liter (1000 ml) of solution. Molality M Moles of solute in 1000 gm of solvent. Normality N Gram equivalent weights of solute in 1 liter of solution Mole Fraction X Ration of moles of solute to total moles of solute+ solvent Percentage by Weight % w/w gm of solute in 100 gm of solution Percentage by Volume %v/v ml of solute in 100 ml of solution Percentage Weight in Volume % w/v gm of solute in 100 ml of solution c) Pharmaceutical Compendia: Term Parts of solvent required for 1 part of solute Very soluble Less than 1 part Freely soluble 1 to 10 parts Soluble 10 to 30 parts Sparingly soluble 30 to 100 parts Slightly soluble 100 to 1000 parts Very slightly soluble 1000 to 10 000 parts Practically insoluble More than 10 000 parts DISTRIBUTION LAW, ITS LIMITATIONS AND APPLICATIONS "If a solute X distributes itself between two immiscible solvents A & B at constant temperature & X is in the same molecular condition in both the solvents, then: concentration of X in A / Concentration of X in B = K".
  • If C 1 and C 2 are the equilibrium concentrations of the substance in Solvent A and Solvent B, respectively, the equilibrium expression becomes- K = C 1 /C 2
  • The equilibrium constant, K , is known as the distribution ratio, distribution coefficient , or partition coefficient.
  • Partition coefficients have no units.
  • Drugs partition themselves between the aqueous phase and lipophilic membrane.
  • If, K>1 = drug is more lipophilic.
  • If, K<1= drug is more hydrophilic.
  • Hydrophilic drugs with low partition coefficient are found in hydrophilic compartments such as blood serum.
  • Hydrophobic drugs with high partition coefficients are preferentially distributed to hydrophobic compartments such as bilipid layers of cells.
  • It is a measure of how well substance partitions between lipid and water. Limitations:
  1. Non-miscibility of solvents
  2. Equilibrium concentration
  3. Same molecular state
  4. Constant temperature
  5. Dilute solutions Applications:
  6. Release of drug from dosage forms.
  7. Passage of drug through membranes
  1. Effective concentration of preservative can be established for the storage of emulsion and other dosage forms.
  2. Solubility of drugs in water and other solvents and in mixture of solvents can be predicted.
  3. The oil-water partition coefficients are indicative of lipophilic hydrophilic character of drug molecules. UNIT-II Q.1 Discuss in detail properties of the various states of matter. How does transition take place from one state of matter to other? Or, Define the following- i) enthalpy, ii) entropy, iii) triple point, iv) vapour pressure. Answer: CHANGES IN THE STATE OF MATTER
  • Enthalpy: Enthalpy is a measure of the total heat content of a system.
  • Entropy: Entropy is a measure of the disorder of a system.
  • Triple point: The triple point of any substance is that temperature and pressure at which the material can coexist in all three phases (solid, liquid and gas) in equilibrium. Specifically the triple point of water is 273.16 K at 611.2 Pa.

Q.4 Differentiate between crystalline solid and amorphous solid. Answer: Q.5 What do you understand by polymorphism? Write its importance in pharmacy. Answer: Polymorphism: Polymorphism is the ability of solid materials to exist in two or more crystalline forms with different arrangements or conformations of the constituents in the crystal lattice.

  • Different crystalline forms are called polymorphs.
  • Polymorphs are of 2 types :
    1. Enatiotropic: can be changed from one form into another by varying temp or pressure. Eg. Sulphur.
    2. Monotropic: unstable at all temp & pressure. Eg. Glyceryl stearate. Importance of polymorphism in pharmacy: Polymorphs differ from each other with respect to their physical property such as:
    • Solubility
    • Melting point
    • Density
    • Hardness
    • Compression characteristic
  • Eg. Chloromphenicol exist in A,B & C forms, of these B form is more stable & most preferable.
  • These forms also differ in various important drug out comes like drug efficacy, bioavailability, and even toxicity. UNIT-III Q.1 Write the applications of surfactants in pharmacy. Or, Explain the term solubilization and detergency. Or, Discuss with examples interfacial phenomenon in pharmacy. Answer: Applications of surfactants in pharmacy: Solubilization Detergency
  • The property of surfactant to cause an increase in the solubility of organic compounds in aqueous systems is called
  • Detergents are surfactants used for removal of dirt.
  • Detergency involves:

solibilization.

  • This property is exhibited at or above CMC only which indicates that mecelles are involved in the phenomenon. - Initial wetting of the dirt and the surface to be cleaned. - Deflocculation of suspension, emulsification or solubilisation of dirt particles. - Finally washing away the diert. Q.2 Classify surfactants on the basis of ionization. Answer: Q.3 Enlist various methods used in measurement of interfacial tension. How will you measure surface and interfacial tensions by capillary rise and Du Nouy ring method? Answer: Methods used in measurement of surface and interfacial tension:
  • Capillary rise method ( only for surface tension)
  • Drop weight and count method ( only for surface tension)
  • Wilhelmy plate method
  • Du Nouy Tensiometer or ring detachment method
  • Spreading coefficient (S) is the difference between work of adhesion and work of cohesion.
  • S= Wa – Wc = (γL + γS - γLS) - 2γL = γS - γL - γLS
  • S = γS – (γL + γLS)
  • Where, γS = surface tension of spreading liquid γL = surface tension of sublayer liquid γLS = interfacial tension
  • Spreading occurs when Spreading coefficient (S) is positive i.e. γS> (γL + γLS)
  • Spreading liquid forms globules or floating lens that is spreading will not take place when Spreading coefficient (S) is negative i.e. γS< (γL + γLS) Q.5 Describe the HLB scale. What are the applications of HLB in pharmacy? Give any one method for determining HLB. Answer: HLB scale:
  • The relationship ( or balance) between the hydrophilic portion of the non-ionic surfactant to the lipophilic portion.
  • It was invented in 1954 by William C. Griffin.
  • As a guidance to good emulsification performance.
  • HLB values are calculated for non-ionic surfactants only.
  • The HLB value is an indication of the solubility of the surfactant. Method for determining HLB:
  • Griffin’s mathematical method: HLB = 20 × (Mh/ M)
  • Mh = molecular weight of hydrophilic groups
  • M = molecular weight of the whole molecule
  • Eg. Mono oleic acid ester: non-ionic surfactant
  • Mh = 396 [ ethylene oxide chain ( OCH 2 CH 2 ) 9 = 396]
  • M = 671

- HLB = 20 × (396 / 671) = 11.

Applications of HLB value and those surfactants in pharmacy:

HLB value Use Example 1 - 3 Antifoaming Agent Oleic Acid 4 - 6 Emulsifying Agent W/O Span 80 7 - 8 Emulsifying Agent W/O; Wetting and Spreading Agents Span 20 9 - 12 Emulsifying Agent O/W; Wetting and Spreading Agents Methyl Cellulose 13 - 15 Emulsifying Agents O/W ; Detergents Tween 16 Emulsifying Agent O/W; Detergents, Solubilizing Agents Tween 17 - 20 Solubilizing Agents Sodium oleate 40 Everything Sodium Lauryl Sulfate (Tide) UNIT-IV Q.1Define complexation. Describe metal complexes and organic molecular complexes. Answer: Complexation: I.METAL COMPLEXES:

  • METAL (substrate)- central atom
  • BASE (ligand)- Electron pair donor
  • COMPLEX formed by co-ordination bond

C) CLATHRATES

Q.3 What are the different methods for studying complex formation? Discuss in detail the solubility method to determine the formation of a complex and its stability constant. Answer: DIFFERENT METHODS FOR STUDYING COMPLEX FORMATION:

  1. Method of continuous variation
  2. Distribution method
  3. Solubility method
  4. pH titration method SOLUBILITY METHOD:
  • When mixture forms complexes, solubility may increase or decrease.
  • Experiments are conducted to estimate parameters. Experiment:
  1. Caffeine (Complexing agent) taken in different concentrations.
  2. Add PABA, agitate, filter and analyze drug content.

Q.4 How the binding of drugs to proteins can influence their action? Deduce an equation for Scatchard plot for drug- protein interaction. Answer: Binding of drugs to proteins can influence:

  • Facilitate the distribution of drugs into the body.
  • Inactivating the drug
  • Retarding the excretion of drug
  • Interaction of a drug with proteins
  • Displacement of body hormones or coadministered agent.
  • Configurational change in the protein
  • Formation of drug-protein complex that is biologically active.
  • Important proteins: albumin and alpha1-acid glycoprotein Equation for Scatchard plot for drug- protein interaction:
  • The interaction between a protein (P) and a drug molecule (D) for a simple case of 1:1 protein drug complex can be represented as: P+D PD
  • Applying the law of mass action, the expression becomes: K= [PD] / [P] [D] Or, [PD] = K[P] [D] Where, K= association constant [P]= conc of unbound protein in terms of free binding sites [D]= conc of unbound drug [PD]= conc of protein- drug complex
  • If the total protein conc in the body is designated as [Pt], we can write: [Pt]=[P]+[PD]
  • Since the total protein conc is the sum of the unbound protein and the protein present in the complex or, [P]=[Pt]+[P]
  • Substituting for [P] in the above equation, we get: [PD] = K[D] ( [Pt] – [PD] ) or, [PD] = K[D][Pt] – K[D] [PD] or, [PD] + K[D] [PD] = K[D][Pt] or, [PD] (1 + K[D] ) = K[D][Pt] or, [PD] / [Pt] = K[D] / (1 + K[D] ) - Where, [PD] / [Pt], represents the average number of drug molecules bound per mole of protein [Pt]. - Replacing [PD] / [Pt] by r, we get: r = K[D] / (1 + K[D] ) - Suppose there are n number of independent binding sites, then: r = n K[D] / (1 + K[D] ) ………….(1) - The equation (1) can be modified to obtain a plot, known as the Scatchard plot. r (1 + K[D] ) = nK[D] or, r + rK[D] = nK[D] or, r = nK[D] - rK[D] or, r = [D] (nK – rK) or, r / [D] = (nK – rK) …………(2)
  • Scatchard plot is plotted against ‘r’ to give straight line if only one class of binding sites exists.
  • if more than one class of binding sites exists, the graph is not linear.
  • The region with pH values below 7 is designated as a acidic and above pH 7.0 is designated as basic (or alkaline). **IMPORTANT BIOLOGICAL BUFFER SYSTEMS:
  1. BLOOD:**
  • maintained at a pH of about 7.4.
  • plasma contains carbonic acid/bicarbonate and acid/alkali sodium salts of phosphoric acid as buffers.
  • Plasma proteins, which behave as acids in blood, can combine with bases and so act as buffers.
  • In the erythrocytes, the two buffer systems consist of hemoglobin/oxyhemoglobin and acid/alkali potassium salts of phosphoric acid. 2. URINE:
  • The 24-hr urine collection of a normal adult has a pH averaging about 6.0 units; it may be as low as 4. or as high as 7.8.
  • When the pH of the urine is below normal values, hydrogen ions are excreted by the kidneys.
    • Conversely, when the urine is above pH 7.4, hydrogen ions are retained by action of the kidneys in order to return the pH to its normal range of values. Q.2 Elaborate the electrometric and colorimetric pH determination methods. Answer: ELECTROMETRIC METHOD: Principle: to determine the activity of the hydrogen ion by potentiometric measurement using a standard hydrogen electrode and a reference electrode. Procedure:
  • A pH meter is composed of a probe, which is formed by two electrodes.
  • This probe passes electrical signals to a meter that displays the reading in pH units.
  • The measuring and reference electrode together form an electrolytic cell.
  • A voltage difference occurs due to its differences in the electron mobility produced by the two electrodes.
  • This net voltage is recorded and calibrated as a function of the pH of the measuring liquid. COLORIMETRIC METHOD: Principle: developing colour in the sample with an indicator dye and comparing the colour of solution of unknown pH with intensity of solution of known pH, concentration of unknown solution can be determined. Procedure: colour can be measured visually or electronically. a). Visual method of estimation:
    • Different kits are available to determine pH.
    • After adding reagent, the color of unknown solution in test tube is compared with standard to determine pH value. b). Electronic method of estimation:
    • Take the sample in two square tubes upto same level.
    • Put 2-3 drops of indicator in one tube and put it in the right hand side compartment.
    • Place the blank (tube without indicator) in left hand side compartment.
    • Rotate the disc till the color developed in the right hand side compartment coincides with the disc color.
    • Note the corresponding pH and recorded. Q.3 Define buffer capacity. Give examples of pharmaceutical buffers. Answer: BUFFER CAPACITY: “A measure of its magnitude of its resistance to change in pH in the addition of an acid or a base.” ΔA or ΔB β = ΔpH PHARMACEUTICAL BUFFERS:
  • Pharmaceutical Buffers solutions are used frequently in pharmaceutical practice, particularly in the formulation of ophthalmic solutions.
  • Many buffers are available today. One of the most common biological buffers is phosphate buffered saline (PBS).
  • Phosphate buffered saline contains sodium chloride (NaCl) and dibasic sodium phosphate (Na2PO4).
  • It may also contain potassium chloride (KCl), monobasic potassium phosphate (KH2PO4), calcium chloride (CaCl2), and magnesium sulfate (MgSO4).