The Ellingham Diagram: Thermodynamics Deciding an Industrial Process

September 17, 2026

| Chemical Science Exams, Physical Chemistry

Physical Chemistry · Applied The Ellingham Diagram: Thermodynamics Deciding an Industrial Process A single plot that answers which reducing agent will work, and at what temperature, for any metal oxide. BSc & MSc · Physical Chemistry · Concept The short answer: The diagram plots the standard free energy of oxide formation against temperature. A metal whose line lies lower can reduce the oxide of one whose line lies higher. Most lines slope upward because forming a solid oxide consumes gas, but the carbon monoxide line slopes downward, which is why carbon becomes a universal reducing agent at high temperature. What…

Inductive, Resonance and Hyperconjugative Effects Compared

September 17, 2026

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| Chemical Science Exams, Organic Chemistry

Organic Chemistry · Fundamentals Inductive, Resonance and Hyperconjugative Effects Compared Three ways electron density is redistributed. Nearly every stability and acidity argument in organic chemistry is one of these three applied carefully. BSc & MSc · Organic Chemistry · Concept The short answer: The inductive effect is transmitted through sigma bonds and falls off rapidly with distance. Resonance involves delocalisation of pi electrons or lone pairs and can act over long distances but requires suitable geometry. Hyperconjugation involves sigma electrons overlapping with an adjacent empty or pi orbital. The three effects Inductive Resonance Hyperconjugation Transmitted through Sigma bonds Pi system…

Amino Acids and Peptides: Zwitterions, pI and the Peptide Bond

September 16, 2026

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| Chemical Science Exams, Organic Chemistry

Organic Chemistry · Biomolecules Amino Acids and Peptides: Zwitterions, pI and the Peptide Bond Almost every property of an amino acid follows from the fact that it carries an acid and a base in the same molecule. BSc & MSc · Organic Chemistry · Concept The short answer: An amino acid exists as a zwitterion at intermediate pH, which explains its high melting point and water solubility. The isoelectric point is the pH at which net charge is zero, and it determines behaviour in electrophoresis. The peptide bond has partial double bond character, making it planar and restricting rotation. The…

Determining Polymer Molar Mass: Which Average and Which Method

September 16, 2026

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| Chemical Science Exams, Physical Chemistry

Physical Chemistry · Macromolecules Determining Polymer Molar Mass: Which Average and Which Method A polymer has no single molar mass, so the method you choose determines which average you get — and the two can differ substantially. BSc & MSc · Physical Chemistry · Concept The short answer: A polymer sample contains chains of many lengths, so its molar mass is an average. Colligative methods count particles and give the number average; light scattering weights by mass and gives the weight average; viscosity gives a third value between them. Their ratio measures how broad the distribution is. Why there is…

Oxidation Methods Compared: Choosing the Right Reagent

September 16, 2026

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| Chemical Science Exams, Organic Chemistry

Organic Chemistry · Reagents Oxidation Methods Compared: Choosing the Right Reagent The commonest exam error in oxidation is choosing a reagent that goes one step too far. BSc & MSc · Organic Chemistry · Method The short answer: A primary alcohol can be oxidised to an aldehyde or all the way to a carboxylic acid, and the reagent decides which. Anhydrous chromium reagents stop at the aldehyde; aqueous strong oxidants do not. Secondary alcohols give ketones, and tertiary alcohols resist oxidation entirely. The alcohol oxidation problem Substrate Mild, anhydrous conditions Strong, aqueous conditions Primary alcohol Aldehyde Carboxylic acid Secondary alcohol…

ESR Spectroscopy: Detecting and Identifying Unpaired Electrons

September 16, 2026

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| Chemical Science Exams, Physical Chemistry

Physical Chemistry · Spectroscopy ESR Spectroscopy: Detecting and Identifying Unpaired Electrons A technique that sees only species with unpaired electrons, which makes it uniquely selective for radicals and certain metal complexes. BSc & MSc · Spectroscopy · Concept The short answer: An unpaired electron in a magnetic field has two spin states, and transitions between them are observed in the microwave region. The g value locates the signal and identifies the environment; hyperfine splitting by nearby magnetic nuclei reveals where the unpaired electron is delocalised. The basic phenomenon An electron has spin, and in a magnetic field its two spin…

Acid–Base Theories Compared, and When Each One Runs Out

September 15, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Acids and Bases Acid–Base Theories Compared, and When Each One Runs Out Each theory was proposed because the previous one could not describe something. Knowing what each failed at is more useful than the definitions. BSc & MSc · Inorganic Chemistry · Concept The short answer: Arrhenius requires water and describes only proton and hydroxide chemistry. Brønsted–Lowry generalises to proton transfer in any solvent. Lewis abandons the proton entirely and defines acidity as electron pair acceptance, which covers metal ions and molecules with no hydrogen at all. The three theories and their limits Theory Acid is Base…

Isomerism in Coordination Compounds: Every Type With Its Test

September 15, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Coordination Isomerism in Coordination Compounds: Every Type With Its Test Seven kinds of isomerism, each distinguished by a specific experiment. Knowing which experiment goes with which type is what the questions test. BSc & MSc · Inorganic Chemistry · Concept The short answer: Structural isomers differ in which atoms are bonded to what — ionisation, hydrate, linkage and coordination isomerism. Stereoisomers have the same connectivity but different arrangement in space — geometrical and optical. Each type has a characteristic experiment that reveals it. Structural isomerism Type What differs How it is detected Ionisation Which anion is inside…

Silicates and Silicones: Structure From One Building Block

September 15, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Main Group Silicates and Silicones: Structure From One Building Block Every silicate is built from the same tetrahedron. What varies is how many corners are shared, and that single number determines the structure. BSc & MSc · Inorganic Chemistry · Concept The short answer: A silicate tetrahedron shares between zero and four of its corner oxygens with neighbours. Sharing none gives discrete anions, two gives chains or rings, three gives sheets, and four gives a three-dimensional network. Silicones are synthetic polymers with a silicon–oxygen backbone and organic side groups. The building block Every silicate contains silicon at…

Carbocation Rearrangements: Predicting the Unexpected Product

September 15, 2026

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| Chemical Science Exams, Organic Chemistry

Organic Chemistry · Mechanism Carbocation Rearrangements: Predicting the Unexpected Product When the product has a skeleton different from the starting material, a carbocation rearranged. Knowing when to expect it is most of the skill. BSc & MSc · Organic Chemistry · Concept The short answer: A carbocation rearranges when a hydride or alkyl group can migrate from an adjacent carbon to give a more stable cation. The migration is concerted with nothing else and requires no reagent. Recognising that a more stable cation is available is what predicts the rearranged product. The stability ladder tertiary > secondary > primary >…

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