GPAT Physical Pharmacy Syllabus

Physical Pharmacy syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Physical Pharmacy in GPAT, not a summary of it.

1. 1

   Buffer

   overview

   Examined as a single unit within Physical Pharmacy — no further topic split in the official outline.

2. 2

   Solubility

   overview

   Examined as a single unit within Physical Pharmacy — no further topic split in the official outline.

3. 3

   Matter, properties of matter

   overview

   Examined as a single unit within Physical Pharmacy — no further topic split in the official outline.

4. 4

   Viscosity and rheology

   overview

   Examined as a single unit within Physical Pharmacy — no further topic split in the official outline.

5. 5

   Surface and interfacial phenomenon

   overview

   Examined as a single unit within Physical Pharmacy — no further topic split in the official outline.

6. 6

   Dispersion systems

   overview

   Examined as a single unit within Physical Pharmacy — no further topic split in the official outline.

7. 7

   Complexation

   overview

   Examined as a single unit within Physical Pharmacy — no further topic split in the official outline.

8. 8

   Micromeritics and powder rheology

   overview

   Examined as a single unit within Physical Pharmacy — no further topic split in the official outline.

Physical Pharmacy flashcards for GPAT

24 of 49 cards from the Physical Pharmacy deck — real questions with worked answers.

1. Define solubility and state how it is commonly expressed.

   Solubility is the maximum amount of solute that dissolves in a given quantity of solvent to form a saturated solution at a specified temperature and pressure. It is commonly expressed as mass per volume, molarity, molality, mole fraction, or as a descriptive ratio (e.g., 1 g in mL of solvent).

2. State Noyes-Whitney equation for dissolution and define its terms.

   dC/dt = (D·A/h)(Cs − C), where dC/dt = dissolution rate, D = diffusion coefficient, A = surface area of dissolving solid, h = thickness of diffusion (stagnant) layer, Cs = saturation solubility, and C = concentration in bulk solution at time t.

3. What is the difference between a saturated, unsaturated, and supersaturated solution?

   A saturated solution holds the maximum solute in equilibrium with undissolved solute; an unsaturated solution contains less than the maximum (more can dissolve); a supersaturated solution contains more dissolved solute than equilibrium solubility and is thermodynamically unstable.

4. State the Henderson-Hasselbalch equation for a weak acid and for a weak base.

   Weak acid: pH = pKa + log([salt]/[acid]) = pKa + log([ionized]/[unionized]). Weak base: pH = pKa + log([base]/[salt]) = pKa + log([unionized]/[ionized]).

5. Define partition (distribution) coefficient and give its formula.

   The partition coefficient (P or Ko/w) is the ratio of the concentration of an un-ionized drug distributed between two immiscible solvents at equilibrium: P = C(oil)/C(water). It measures lipophilicity; often expressed as log P.

6. State Noyes-Whitney's relationship under sink conditions and explain sink conditions.

   Under sink conditions, C << Cs, so dC/dt = (D·A·Cs)/h. Sink conditions mean the bulk concentration is kept below ~10-15% of saturation solubility, so dissolution rate is essentially constant and not slowed by build-up of dissolved drug.

7. What is the Brunauer-Emmett-Teller (BET) theory used for?

   BET theory describes multilayer physical adsorption of gas molecules on a solid surface and is used to determine the specific surface area of powders/solids from gas (usually nitrogen) adsorption data.

8. State the Freundlich and Langmuir adsorption isotherm equations.

   Freundlich: x/m = k·C^(1/n) (empirical, multilayer). Langmuir: x/m = (a·b·C)/(1 + b·C) (monolayer, assumes uniform sites). Here x/m = amount adsorbed per gram adsorbent, C = equilibrium concentration.

9. Define surface tension and interfacial tension, including units.

   Surface tension is the force per unit length acting on the surface of a liquid in contact with air/vapor; interfacial tension is the force per unit length at the interface between two immiscible liquids. Both have units of dyne/cm (or mN/m).

10. What is the difference between cohesion and adhesion in spreading?

    Work of cohesion is the energy to separate a liquid from itself (Wc = 2γ); work of adhesion is the energy to separate two different phases (Wa = γa + γb − γab). Spreading occurs when adhesion exceeds cohesion (positive spreading coefficient).

11. Define HLB and state the HLB ranges for key surfactant functions.

    HLB (Hydrophilic-Lipophilic Balance) measures the balance of hydrophilic and lipophilic groups in a surfactant. Ranges: 3-6 = w/o emulsifier, 7-9 = wetting agent, 8-18 = o/w emulsifier, 13-15 = detergent, 15-18 = solubilizing agent.

12. What is critical micelle concentration (CMC)?

    CMC is the surfactant concentration above which surfactant molecules spontaneously aggregate into micelles. Below CMC surfactant exists as monomers; at CMC abrupt changes occur in surface tension, conductivity, and turbidity.

13. State the Young-Laplace equation for pressure across a curved surface.

    ΔP = 2γ/r for a spherical droplet (or bubble single surface), where ΔP = pressure difference across the interface, γ = surface tension, and r = radius of curvature. For a soap bubble (two surfaces): ΔP = 4γ/r.

14. State the Stokes' law equation for sedimentation velocity.

    v = d²(ρs − ρ0)g / 18η, where v = sedimentation velocity, d = particle diameter, ρs = particle density, ρ0 = medium density, g = gravitational acceleration, and η = medium viscosity.

15. What are the types of flow exhibited by non-Newtonian fluids?

    Plastic (Bingham), pseudoplastic (shear-thinning), and dilatant (shear-thickening) flow. Time-dependent types include thixotropy (shear-thinning reversible with time) and rheopexy/antithixotropy (shear-thickening with time).

16. Differentiate Newtonian and non-Newtonian fluids.

    Newtonian fluids have viscosity independent of shear rate (constant slope; e.g., water, glycerin, light oils). Non-Newtonian fluids have viscosity that changes with shear rate or time (e.g., colloids, emulsions, suspensions, gels).

17. Define viscosity and fluidity, with units of viscosity.

    Viscosity (η) is a fluid's resistance to flow (internal friction); units are poise (dyne·s/cm²) or Pa·s (1 Pa·s = 10 poise). Fluidity (φ) is the reciprocal of viscosity, φ = 1/η.

18. What is thixotropy and why is it desirable in pharmaceutical suspensions?

    Thixotropy is the reversible, time-dependent decrease in viscosity under shear and recovery of structure (gel-sol-gel) on standing. It is desirable in suspensions/gels because the product is easy to pour/shake but forms a gel on standing to prevent caking and sedimentation.

19. State the Einstein viscosity equation for dilute colloidal dispersions.

    η = η0(1 + 2.5φ), where η = viscosity of dispersion, η0 = viscosity of dispersion medium, and φ = volume fraction of dispersed (spherical) particles. Valid for dilute dispersions of rigid spheres.

20. Classify colloidal systems based on interaction with the dispersion medium.

    Lyophilic (solvent-loving, e.g., gelatin, acacia, proteins; thermodynamically stable, reversible), lyophobic (solvent-hating, e.g., metal/sulfur sols; unstable, irreversible), and association (amphiphilic) colloids formed by surfactant micelles above CMC.

21. What is the Tyndall effect and which colloidal property does it demonstrate?

    The Tyndall effect is the scattering of a light beam by colloidal particles, making the beam visible. It demonstrates the optical property of colloids and distinguishes colloidal dispersions from true solutions.

22. What is the DLVO theory used to explain?

    DLVO (Derjaguin-Landau-Verwey-Overbeek) theory explains the stability of lyophobic colloids/dispersions as the balance between attractive van der Waals forces and repulsive electrical double-layer forces; the net potential energy curve predicts coagulation or stability.

23. Define zeta potential and its significance in dispersion stability.

    Zeta potential is the electric potential at the plane of shear (slipping plane) around a charged particle in a dispersion. Higher absolute zeta potential (>±30 mV) means greater repulsion and better stability against aggregation/flocculation.

24. State the Schulze-Hardy rule for coagulation of colloids.

    The Schulze-Hardy rule states that the coagulating (flocculating) power of an electrolyte is determined by the valency of the ion opposite in charge to the colloid; the higher the valency, the greater the coagulating power (e.g., Al³⁺ > Ca²⁺ > Na⁺ for a negative sol).

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