English for Chemistry: Essential Vocabulary & Phrases

"titration"

A quantitative analytical technique in which a solution of known concentration is added to a solution of unknown concentration until the reaction reaches its endpoint

"The student performed an acid-base titration using sodium hydroxide to determine the exact concentration of the hydrochloric acid sample."

"centrifugation"

A separation technique that uses centrifugal force to sediment particles or separate components of different densities

"After the reaction, the mixture was subjected to centrifugation at 3000 rpm for ten minutes to pellet the precipitate."

"reflux"

A technique in which a reaction mixture is boiled continuously while the vapour is condensed and returned to the flask, allowing long reaction times without loss of solvent

"The esterification was carried out under reflux conditions for four hours to ensure complete conversion of the reactants."

"chromatography"

A family of separation techniques based on differential migration of components through a stationary phase carried by a mobile phase

"Thin-layer chromatography confirmed the presence of two distinct products in the reaction mixture before column purification."

"spectroscopy"

The study of the interaction between matter and electromagnetic radiation, used to identify and quantify chemical substances

"Infrared spectroscopy revealed a broad absorption peak at 3300 cm⁻¹, indicating the presence of a hydroxyl group in the compound."

"filtration under reduced pressure"

A filtration technique using a Buchner funnel and vacuum pump to accelerate the separation of a solid from a liquid

"The crude product was collected by filtration under reduced pressure and washed with ice-cold solvent to remove impurities."

"recrystallisation"

A purification technique in which an impure solid is dissolved in a hot solvent and allowed to crystallise slowly upon cooling

"Recrystallisation from ethanol yielded colourless needle-shaped crystals with a melting point matching the literature value."

"titration endpoint"

The point in a titration at which the indicator changes colour or a measurable property changes sharply, signalling that the equivalence point has been reached

"A persistent pink colour indicated the titration endpoint had been reached and no further base was required."

"electrophilic substitution"

A reaction in which an electrophile replaces a hydrogen atom or another substituent on an aromatic ring or other electron-rich molecule

"Bromination of benzene proceeds by electrophilic substitution, with the bromine acting as the electrophile in the presence of a Lewis acid catalyst."

"nucleophilic addition"

A reaction in which a nucleophile donates a pair of electrons to an electrophilic carbon, forming a new covalent bond

"The nucleophilic addition of a Grignard reagent to a ketone is a versatile method for constructing carbon–carbon bonds."

"stereoisomers"

Compounds with the same molecular formula and connectivity but different spatial arrangements of their atoms

"The two stereoisomers of lactic acid rotate plane-polarised light in opposite directions and cannot be superimposed on each other."

"functional group"

A specific atom or group of atoms within a molecule that is responsible for its characteristic chemical reactions

"The carbonyl functional group in aldehydes makes them far more reactive toward nucleophiles than simple alkanes."

"leaving group"

An atom or group that departs with a pair of electrons during a substitution or elimination reaction

"Bromide is an excellent leaving group in SN2 reactions because the C–Br bond is relatively weak and polarised."

"conjugation"

The overlap of adjacent p orbitals across alternating single and double bonds, delocalising electrons and stabilising the molecule

"Extended conjugation in beta-carotene is responsible for its strong absorption of visible light, giving the molecule its orange colour."

"retrosynthetic analysis"

A problem-solving approach in which a target molecule is mentally disconnected into simpler precursor fragments to plan a synthetic route

"Retrosynthetic analysis of the natural product revealed that a Diels–Alder reaction could assemble the bicyclic core in a single step."

"protecting group"

A temporary chemical modification that blocks a reactive functional group during a multi-step synthesis to prevent unwanted side reactions

"The alcohol was converted to a TBS ether as a protecting group before the oxidation step to prevent over-reaction."

"Gibbs free energy"

A thermodynamic potential that measures the maximum reversible work available from a system at constant temperature and pressure, predicting the spontaneity of a reaction

"A negative Gibbs free energy change confirmed that the dissolution process was thermodynamically spontaneous under standard conditions."

"activation energy"

The minimum energy that reacting molecules must possess to overcome the energy barrier and form products

"Adding a catalyst lowers the activation energy of the decomposition reaction, allowing it to proceed rapidly at room temperature."

"rate constant"

A proportionality constant in the rate law that relates the reaction rate to the concentrations of reactants at a given temperature

"The rate constant for the hydrolysis doubled when the temperature was raised by 10 degrees, consistent with the Arrhenius equation."

"entropy"

A thermodynamic state function measuring the degree of disorder or the number of accessible microstates in a system

"The large positive entropy change accompanying the dissolution of the salt was the main driving force for the endothermic process."

"equilibrium constant"

A dimensionless ratio of the concentrations of products to reactants at equilibrium, each raised to the power of their stoichiometric coefficients

"An equilibrium constant greater than one indicated that the reaction strongly favoured product formation under standard conditions."

"molecular orbital theory"

A quantum mechanical model describing chemical bonding in terms of wavefunctions that extend over the entire molecule

"Molecular orbital theory correctly predicts that oxygen is paramagnetic due to two unpaired electrons in degenerate antibonding orbitals."

"Henry's law"

A gas law stating that the amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid at constant temperature

"Henry's law was applied to calculate the concentration of dissolved carbon dioxide in the pressurised beverage sample."

"half-life"

The time required for the concentration of a reactant, or the activity of a radioactive isotope, to fall to half of its initial value

"The first-order decomposition of hydrogen peroxide in this solution had a half-life of approximately 24 hours at room temperature."

"limit of detection"

The lowest concentration of an analyte that can be reliably distinguished from background noise under stated analytical conditions

"The optimised HPLC method achieved a limit of detection of 0.5 nanograms per millilitre for the target pesticide residue."

"calibration curve"

A graph plotting instrument response against known analyte concentrations, used to determine the concentration of unknowns

"A linear calibration curve was constructed from six standard solutions before analysing the environmental water samples."

"mass spectrometry"

An analytical technique that ionises chemical species and sorts the resulting ions by their mass-to-charge ratio to determine molecular masses and structures

"High-resolution mass spectrometry provided the exact molecular formula and confirmed the identity of the synthesised compound."

"matrix effect"

The influence of co-extracted sample components on the analytical signal, causing it to differ from what would be observed in a pure solvent

"The strong matrix effect observed in soil extracts required standard addition calibration rather than external standards."

"precision and accuracy"

Precision is the reproducibility of repeated measurements; accuracy is how closely a measured value agrees with the true value

"The new method demonstrated both high precision, with a relative standard deviation below 2%, and excellent accuracy when tested on certified reference materials."

"blank correction"

The subtraction of the signal measured in a sample containing no analyte from all analytical measurements, to account for background interference

"A reagent blank correction was applied to compensate for trace iron contamination in the concentrated acid used for digestion."

"signal-to-noise ratio"

The ratio of the analytical signal to the background noise, used as a measure of the sensitivity and reliability of a measurement

"Increasing the signal-to-noise ratio by signal averaging allowed detection of the minor product at concentrations below 1 ppm."

"standard addition"

A calibration technique in which known amounts of analyte are added to aliquots of the sample to correct for matrix effects

"Standard addition was necessary for the blood serum analysis because the complex protein matrix significantly suppressed the ionisation signal."

"safety data sheet"

A standardised document (SDS) providing detailed information on a chemical substance's properties, hazards, handling, storage, and emergency procedures

"Before handling the reagent, the technician consulted the safety data sheet and confirmed that the chemical required a fume hood and nitrile gloves."

"risk assessment"

A systematic evaluation of the potential hazards associated with a chemical or experimental procedure, together with measures to control those hazards

"A thorough risk assessment was completed before commencing the large-scale synthesis, identifying fire and toxic vapour exposure as the primary hazards."

"GHS pictogram"

One of nine standardised symbols used in the Globally Harmonised System of Classification and Labelling of Chemicals to communicate hazard information

"The skull and crossbones GHS pictogram on the label warned that the solvent was acutely toxic if ingested or inhaled."

"exposure limit"

The maximum permissible airborne concentration of a hazardous substance to which workers may be exposed over a defined time period

"The atmospheric monitoring showed benzene concentrations well below the occupational exposure limit of 1 ppm over eight hours."

"peer review"

The evaluation of a scientific manuscript, grant proposal, or data set by independent experts with relevant subject knowledge before publication or approval

"The research paper was accepted following peer review by three independent chemists who recommended minor revisions to the experimental section."

"yield"

The amount of product obtained in a chemical reaction, expressed as a percentage of the theoretical maximum based on stoichiometry

"Optimising the reaction temperature and solvent system improved the yield of the target compound from 45% to 78%."

"experimental error"

The difference between a measured value and the true value, arising from limitations in equipment, technique, or random variation

"The discrepancy between the measured and theoretical melting points was within the expected experimental error of ±1 degree Celsius."

"waste disposal protocol"

A set of procedures specifying how chemical waste must be segregated, labelled, stored, and disposed of in compliance with environmental regulations

"All halogenated solvent waste was collected in designated containers according to the waste disposal protocol and sent for licensed incineration."

"coordination complex"

A species consisting of a central metal atom or ion bonded to surrounding molecules or ions (ligands) through coordinate covalent bonds

"The deep blue colour of the solution was due to the formation of a copper–ammonia coordination complex with four ammonia ligands."

"oxidation state"

A formal charge assigned to an atom in a molecule or ion, representing the number of electrons it has lost or gained relative to its elemental form

"In permanganate ion, manganese has an oxidation state of +7, making it a powerful oxidising agent in acidic solution."

"lattice energy"

The energy released when gaseous ions of opposite charge combine to form one mole of an ionic solid, reflecting the strength of the ionic lattice

"The very high lattice energy of magnesium oxide explains its extremely high melting point and use as a refractory material."

"X-ray diffraction"

A technique for determining the atomic structure of crystalline materials by analysing the diffraction pattern produced when X-rays interact with the crystal lattice

"X-ray diffraction analysis confirmed the cubic crystal structure and determined the unit cell parameters of the newly synthesised perovskite."

"band gap"

The energy difference between the valence band and conduction band in a semiconductor or insulator, determining its optical and electrical properties

"The narrow band gap of 1.1 eV makes silicon suitable for photovoltaic applications, as it can absorb a significant portion of the solar spectrum."

"ligand field theory"

A model explaining the electronic structure and properties of coordination complexes in terms of the splitting of metal d orbitals by surrounding ligands

"Ligand field theory predicts that octahedral cobalt(III) complexes with strong-field ligands are diamagnetic, which was confirmed experimentally."

"redox reaction"

A chemical reaction involving the simultaneous transfer of electrons from one species (oxidation) to another (reduction)

"In the corrosion of iron, a spontaneous redox reaction occurs between iron metal and dissolved oxygen in the presence of water."

"sol-gel process"

A wet-chemical synthesis method for producing solid materials, especially metal oxides, by converting a solution (sol) into a gel and then drying or firing it

"Titanium dioxide nanoparticles with a controlled particle size were prepared using the sol-gel process and calcined at 500 degrees Celsius."