Industrial Chemistry
Most of "industrial chemistry" (dye manufacture, adhesive formulation, country-specific plant processes) is not tested on the MCAT. Two slices of it are: polymer chemistry — how monomers link by addition vs condensation, and why the same logic builds the biological macromolecules you must know — and the separation and purification techniques the AAMC expects in the lab-methods content. This page focuses on exactly those.
Polymers
A polymer is a large molecule (macromolecule) built by repeatedly linking smaller units called monomers; the process is polymerization. The single most testable distinction is the mechanism: addition vs condensation.
The two mechanisms
Monomers with a C=C double bond add to one another with no atoms lost, so the repeat unit has the same empirical formula as the monomer. Proceeds by a reactive intermediate — free-radical, cationic, or anionic — through initiation, propagation, and termination.
- Polyethylene (PE) — from ethylene (CH2=CH2).
- Polypropylene, PVC (vinyl chloride), polystyrene, PTFE (Teflon) — all from substituted ethylenes.
Two functional groups react and eliminate a small molecule (usually H2O) for each new bond — a dehydration synthesis. Each monomer needs two reactive groups. The new linkage is typically an ester or amide.
- Polyesters (e.g. PET) — a diol + a dicarboxylic acid; ester (−COO−) linkages.
- Polyamides (e.g. nylon-6,6) — a diamine + a diacid; amide (−CONH−) linkages.
This is exactly the chemistry of biological macromolecules (next section).
Structure vs property
- Thermoplastics (linear/branched chains) soften and re-melt reversibly on heating — PE, PP, PVC, PET.
- Thermosets are covalently cross-linked into a rigid 3-D network; they cannot be re-melted (analogous to how disulfide cross-links stiffen proteins).
Biological Polymers (why this matters for the MCAT)
The polymers your body is made of are built by the same condensation (dehydration) chemistry as nylon and PET, and broken down by the reverse reaction, hydrolysis (adding water across the bond). Recognizing the monomer, the linkage, and the small molecule lost is repeatedly tested.
| Macromolecule | Monomer | Linkage formed | Small molecule lost |
|---|---|---|---|
| Proteins | amino acids | peptide (amide) bond | H2O |
| Polysaccharides (starch, glycogen, cellulose) | monosaccharides (e.g. glucose) | glycosidic bond | H2O |
| Nucleic acids (DNA, RNA) | nucleotides | phosphodiester bond | H2O |
| Lipids (triacylglycerols) | glycerol + fatty acids | ester bond | H2O |
Every one is a condensation polymer (loses water on synthesis); each is depolymerized by hydrolysis. Note the parallels: the protein peptide bond is an amide, just like nylon; the triacylglycerol linkage is an ester, just like PET. See the Macromolecules notes for the detailed biochemistry.
Separation and Purification Techniques
The AAMC content outline lists these lab methods explicitly. For each, know the physical property it exploits.
Separates liquids by differences in volatility (boiling point). Simple distillation for large boiling-point gaps; fractional distillation for close-boiling mixtures.
Partitions a solute between two immiscible solvents (a separatory funnel). An acid–base extraction exploits the fact that the charged (ionized) form of a compound favors the aqueous layer while the neutral form favors the organic layer.
Separates by how strongly components partition between a mobile phase and a stationary phase. Includes TLC/column (polarity), gel-filtration (size), ion-exchange (charge), and affinity chromatography (specific binding) — the workhorses of protein purification.
Recrystallization purifies a solid using its temperature-dependent solubility. Centrifugation separates particles by density/size. Electrophoresis (e.g. SDS-PAGE) separates macromolecules by size and charge in an electric field.
Worked MCQs
Five MCQs that capture the high-yield testing patterns for industrial chemistry. Read every explanation — the deeper concept lives there.
Q1. Polyethylene is formed from which monomer, and by what mechanism?
Polyethylene (PE) is the addition polymer of ethylene: n CH2=CH2 → (−CH2−CH2−)n. The C=C simply opens and adds with no small molecule lost, so the mechanism is addition (chain-growth), not condensation.
Q2. Nylon-6,6 is best classified as a:
Nylon-6,6 is made from hexamethylenediamine and adipic acid with elimination of water for every amide bond formed — a textbook condensation polymerization. The same amide-forming, water-losing chemistry builds the peptide bonds of proteins.
Q3. Which biological macromolecule is not assembled by condensation (dehydration) polymerization?
Proteins (peptide/amide bonds), nucleic acids (phosphodiester bonds), and polysaccharides (glycosidic bonds) are all built by condensation, losing one water molecule per bond formed. Each is broken down by the reverse reaction, hydrolysis.
Q4. Two organic liquids with boiling points of 65 °C and 80 °C are best separated by:
Two miscible liquids with a modest boiling-point difference are separated by distillation, which exploits differences in volatility. Because the boiling points are relatively close, a fractionating column (fractional distillation) is needed for a clean separation. Filtration and centrifugation separate solids/particles, not miscible liquids.
Q5. A carboxylic acid and a neutral hydrocarbon are dissolved together in an organic solvent. Shaking this solution with aqueous NaOH in a separatory funnel moves the carboxylic acid into the aqueous layer because:
This is an acid–base extraction. NaOH converts the carboxylic acid to its ionized carboxylate salt (R–COO− Na+), which is water-soluble and partitions into the aqueous layer, while the neutral hydrocarbon stays in the organic layer. Acidifying the aqueous layer later regenerates the neutral acid.
Quick Recap
- Addition (chain-growth): monomer has C=C, nothing is lost (PE, PP, PVC, PS, PTFE).
- Condensation (step-growth): two functional groups react and lose a small molecule (usually H2O); forms esters (PET) or amides (nylon).
- Classify by mechanism, not by the bond present.
- All four biological macromolecules are condensation polymers, split by hydrolysis: proteins (peptide/amide), polysaccharides (glycosidic), nucleic acids (phosphodiester), triacylglycerols (ester).
- Separation by property: distillation = boiling point, extraction = solubility (acid–base extraction uses ionization), chromatography = affinity/partitioning, recrystallization = temperature-dependent solubility, electrophoresis/centrifugation = size & charge/density.