The moment PCH 201 stops feeling like two unrelated courses bolted together is the moment it starts making sense. One half asks you to picture a paracetamol molecule in three dimensions and reason about why its shape decides whether it works; the other hands you equations for pH, entropy and reaction rate and expects you to turn them on a real drug. ABUAD Pharmacy students routinely revise the two halves separately and then freeze when a question makes them meet — a buffer calculation that suddenly asks why blood sits at pH 7.4, or a kinetics problem dressed up as an expiry date. This page is a student-written study companion for PCH 201 – Physical Pharmaceutical Chemistry (also listed as PHC 201), a first-semester course for 200 Level students in the ABUAD College of Pharmacy.
What follows condenses the whole syllabus into plain-English notes: the role of chemistry in pharmacy, drugs in the liquid phase, how drugs behave in the body, ionic equilibria, thermodynamics and chemical kinetics. Each topic ends with a targeted exam tip, and there is a set of original practice questions with fully worked answers so you can test yourself rather than just re-read. The complete workbook — with every derivation and worked calculation laid out — sits in the interactive reader at the bottom of this page as a free companion to these notes.
- Course: PCH 201 (PHC 201) – Physical Pharmaceutical Chemistry
- College / Department: College of Pharmacy, Pharmaceutical Chemistry
- Level / Semester: 200 Level, First Semester
- Topics covered: The roles of chemistry in pharmacy, 1D/2D/3D molecular representation and stereochemistry, pharmaceutical systems and dispersions, true solutions and the nine solute–solvent types, colligative/additive/constitutive properties, electrolytes and ideal solutions, the definition and sources of drugs, drug discovery (SAR, QSAR, receptors and the pharmacophore), routes of administration, pharmacokinetics (ADME) and pharmacodynamics, chemical equilibrium and Kw, pH and pOH, Ka/Kb and pKa, the Henderson–Hasselbalch equation, buffers in pharmacy and the body, the four laws of thermodynamics, enthalpy and Hess's law, entropy and Gibbs free energy, drug–receptor binding thermodynamics, and reaction kinetics (rate laws, order, half-life, shelf-life and enzyme kinetics)
- Best for: Continuous assessment + final exam revision
Topics Covered in PCH 201
1. Chemistry in Pharmacy and Molecular Shape
Pharmacy is applied chemistry: every medicine is a chemical entity, and its behaviour is read through overlapping branches — analytical chemistry answers "what and how much is in this product," organic and medicinal chemistry answers "how is the molecule built and how does it react," while physical, computational and biochemistry explain its properties and its action in tissue. The recurring idea in this opening block is that drugs are three-dimensional objects we habitually draw flat. A 2D sketch of paracetamol is as incomplete as using a square to stand for a cube; the real molecule occupies space, and that spatial shape governs how well it fits a receptor. Exam tip: be ready to pair each branch of chemistry with the professional question it answers, and to justify in one sentence why the third dimension (and stereochemistry) matters for drug–receptor fit.
2. Drugs in the Liquid Phase: Dispersions and Solutions
Pharmaceutical mixtures, called dispersions, sort into three classes by particle size: molecular (true solutions, under 1 nm), colloidal (about 1 nm to 0.5 µm) and coarse (above 0.5 µm), and each behaves differently at a filter or a semi-permeable membrane. A true solution is a single-phase molecular dispersion, and because any state of solute can dissolve in any state of solvent there are nine possible solute–solvent combinations, from air (gas in gas) to a gold–silver alloy (solid in solid). Properties then split into colligative (count particles), additive (sum contributions, like molecular weight) and constitutive (depend on arrangement). Exam tip: lock down the particle-size boundaries and microscope visibility of the three dispersion types, and remember that whether a solute is a strong, weak or non-electrolyte decides how many particles it releases — the key to every colligative question.
3. How Drugs Behave in the Body
The WHO defines a drug as a substance used to modify or explore a physiological system or disease state for the recipient's benefit — and because drugs interfere with biology, none is entirely safe (even paracetamol kills in overdose). This block traces drug discovery from natural remedies through Ehrlich's rational synthesis of Salvarsan and his chemotherapeutic index, into SAR, QSAR, receptors, ligands and the binding pharmacophore, then the four sources of drugs (natural, synthetic, semi-synthetic, biosynthetic). It closes on delivery: enteral versus parenteral routes, and ADME — absorption, distribution, metabolism, excretion — where pharmacokinetics (what the body does to the drug) meets pharmacodynamics (what the drug does to the body). Exam tip: keep the therapeutic index (LD₅₀/ED₅₀) distinct from Ehrlich's older chemotherapeutic index, and be able to explain why an oral dose and an IV dose of the same drug behave differently (first-pass metabolism).
4. Ionic Equilibria: pH, pKa and Buffers
This is the most calculation-heavy block and the richest source of marks. It starts from the ionic product of water, Kw = [H⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 25 °C, from which pH + pOH = 14 follows directly. Weak acids and bases only partially ionise, so their strength is compared through Ka, Kb and pKa — and the smaller the pKa, the stronger the acid. The Henderson–Hasselbalch equation, pH = pKa + log([salt]/[acid]), then lets you calculate a buffer's pH, find a pKa, or design a buffer to a target pH. Buffers matter because blood is held near pH 7.4 and parenteral products must match it. Exam tip: practise the four standard problem types — pH of a strong acid/base, pH of a weak acid, buffer pH before and after adding acid, and mass of salt for a target pH — because the numbers change but the method never does.
5. Thermodynamics: Energy, Entropy and Spontaneity
Four laws frame this block. The Zeroth Law makes temperature measurable; the First Law (ΔU = Q − W) conserves energy and introduces enthalpy, where a negative ΔH is exothermic and a positive ΔH endothermic. The Second Law introduces entropy and states that the entropy of the universe rises in any spontaneous change — crucially, a process need not be exothermic to be spontaneous, as melting ice proves. The Third Law fixes the entropy of a perfect crystal at zero at 0 K. It all converges on Gibbs free energy, ΔG = ΔH − TΔS: negative means spontaneous, positive means not, zero means equilibrium, and ΔG° = −RT ln K ties it to the equilibrium constant. Exam tip: memorise the four sign-combinations of ΔH and ΔS (always spontaneous, never spontaneous, and the two temperature-dependent cases), and be ready to find a crossover temperature from T = ΔH/ΔS.
6. Chemical Kinetics and Drug Stability
Kinetics is where the whole course pays off at the pharmacy counter, because it sets shelf life. The rate law, rate = k[A]ˣ[B]ʹ, defines reaction order — and orders must be found by experiment, not read off the balanced equation. The signature result is first-order kinetics, where the half-life t₁/₂ = 0.693/k depends only on k and never on starting concentration, which is why drug elimination and radioactive decay have a fixed half-life; shelf-life t₀ = 0.105/k marks a 10% loss. Zero- and second-order reactions behave differently, and the units of k themselves reveal the order. The block ends with the factors that change rate and with enzyme kinetics via the Michaelis–Menten equation. Exam tip: the fastest way to identify reaction order in an exam is to check which plot gives a straight line — log[A] vs t (first order), 1/[A] vs t (second order), [A] vs t (zero order) — and to read k's units as a cross-check.
Sample Practice Questions (With Answers)
These questions were written from scratch to mirror the style of PCH 201 assessments — a mix of conceptual reasoning and short calculations. Work each one before reading the answer; the goal is to expose the exact idea being tested, not just the final number.
Q1. A colligative property and an additive property both change when you dissolve a solute. What is the essential difference between them, and give one example of each.
Answer: A colligative property depends only on the number of solute particles present, not their chemical identity — osmotic pressure, boiling-point elevation and freezing-point depression are examples, and equal concentrations of different non-electrolytes give roughly equal values. An additive property is the sum of contributions from the individual atoms or components; molecular weight is the classic case. The distinction matters because a strong electrolyte releases more particles than a non-electrolyte at the same concentration, so it has a larger colligative effect.
Q2. Calculate the pH of 0.10 M HCl and of 0.10 M NaOH, and explain why the two answers are not simply mirror images around 7.
Answer: HCl is a strong acid and fully dissociates, so [H⁺] = 0.10 M and pH = −log(0.10) = 1. NaOH is a strong base with [OH⁻] = 0.10 M; using Kw, [H⁺] = 10⁻¹⁴/0.10 = 1.0 × 10⁻¹³ M, so pH = 13. They are mirror images here (1 and 13, symmetric about 7) precisely because both are fully ionised at the same concentration and pH + pOH = 14 — the symmetry breaks only when a weak acid or base is involved, because partial ionisation gives a much smaller ion concentration than the formal concentration suggests.
Q3. A buffer is 0.2 M in both acetic acid and sodium acetate (pKa 4.74). What is its pH, and roughly what happens to that pH if a small amount of strong acid is added?
Answer: By Henderson–Hasselbalch, pH = pKa + log([salt]/[acid]) = 4.74 + log(0.2/0.2) = 4.74, since the ratio is 1. Adding a little strong acid converts some acetate into acetic acid, nudging the ratio below 1, so the pH falls only slightly (in the standard worked case, to about 4.66 — under 0.1 of a unit). That near-constancy is buffer action: added H⁺ is mopped up by acetate ions to form weakly-dissociated acetic acid, so very little free H⁺ results.
Q4. At 298 K a reaction has ΔH = +58.03 kJ and ΔS = +176.6 J K⁻¹. Is it spontaneous, and at what temperature would that change?
Answer: Use ΔG = ΔH − TΔS (convert ΔS to kJ: 0.1766 kJ K⁻¹). ΔG = 58.03 − (298)(0.1766) = 58.03 − 52.63 = +5.40 kJ, which is positive, so the reaction is not spontaneous at 298 K. Because both ΔH and ΔS are positive, this is a temperature-dependent case: it becomes spontaneous once TΔS exceeds ΔH, i.e. above T = ΔH/ΔS = 58.03/0.1766 ≈ 329 K. This is exactly why some reactions "switch on" only when heated.
Q5. A drug decomposes by first-order kinetics with a half-life of 20.0 min. Find the rate constant and the time for the reaction to reach 75% completion. Why doesn't the starting concentration appear in your answer?
Answer: k = 0.693/t₁/₂ = 0.693/20.0 = 0.0347 min⁻¹. At 75% complete, one quarter of the drug remains, so [A]/[A]₀ = 0.25 and t = ln(4)/k = 1.386/0.0347 ≈ 40 min — exactly two half-lives, as expected. The initial concentration is absent because first-order half-life depends only on k; that concentration-independence is the defining fingerprint of first-order kinetics and the reason drug half-lives are quoted as fixed values.
How to Study PCH 201 Effectively
- Treat the equation sheet as a decision tree, not a memory dump: for any ionic-equilibria question, first decide strong vs weak and acid vs base, then pick Kw, the log definition of pH, or Henderson–Hasselbalch — the choice of tool is half the marks.
- Build one master table of the four thermodynamic laws with a single memorable example each (Zeroth = thermometer, First = energy balance, Second = melting ice, Third = perfect crystal at 0 K) so you never confuse them under pressure.
- For kinetics, memorise the three diagnostic straight-line plots and the units of k for each order together — questions almost always hand you data and ask you to identify the order before solving.
- Redraw at least three drugs (start with paracetamol) in 2D and then describe in words what the third dimension adds; this makes the stereochemistry and drug–receptor-fit questions concrete rather than abstract.
- Learn the drug-source tables as pairs (plant → drug → use), e.g. cinchona → quinine → antimalarial, because matching questions are quick, reliable marks if the associations are automatic.
- Always carry units through every calculation and sanity-check the sign of ΔH, ΔS and ΔG at the end — most lost marks in this course are dropped signs and unconverted J-to-kJ, not misunderstood concepts.
Download the Full PCH 201 Practice Workbook
The notes above stand on their own, but if you want the complete picture — every derivation, all the worked Kirchhoff, Hess's-law and Henderson–Hasselbalch calculations, and the full drug-source and thermodynamics tables — the entire PCH 201 workbook is available free in the interactive reader just below. You can read it page by page in your browser or download it to revise offline; treat it as the expanded companion to this summary rather than a replacement for working the problems yourself.
Frequently Asked Questions
Is this PCH 201 material free?
Yes — completely. Both the on-page study guide and the downloadable workbook in the reader are free for ABUAD Pharmacy students to read, save and revise from, with no sign-up or payment. We built it as a revision aid for the College of Pharmacy community, not as a paid product.
Will these exact questions appear in my exam?
No. Every question here was written from scratch by the EverythingABUAD student team to rehearse the reasoning and calculation types PCH 201 tends to test — they are original practice, not leaked or predicted exam questions. Use them to check your understanding; your actual assessment will use its own wording set by your lecturer.
Do I need to be strong at maths to pass the ionic-equilibria and kinetics sections?
You need to be comfortable, not brilliant. The calculations rely on logarithms, simple algebra and unit conversions rather than advanced maths, and the same handful of equations (Kw, pH = −log[H⁺], Henderson–Hasselbalch, ΔG = ΔH − TΔS, and the first/second/zero-order rate laws) recur throughout. If you drill the worked examples until the method is automatic, the arithmetic on the day is the easy part — and getting the pKa and thermodynamics sections solid is often what separates a pass from a strong grade.
About this resource: All summaries, explanations, study tips, and practice questions on this page were written, paraphrased, and adapted by the EverythingABUAD student team to support exam revision. This is an original study aid, not an official ABUAD document, and it is not a prediction of any future exam.
