English is the working language of chemistry: textbooks, research papers, safety data sheets, instrument manuals and supplier catalogs are mostly written in it. Knowing the core words for atoms, bonding, reactions, solutions, lab equipment and analysis helps you follow lectures and lab procedures, write clear reports and work safely with colleagues from other countries.
100 terms
11 topics
49 core terms
200 example sentences
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Atoms and the Periodic Table
atom
noun
Meaning
The smallest unit of an element that keeps its chemical identity. It has a tiny nucleus of protons and neutrons, with electrons moving around it.
Where you use it
Used from the very first lesson. You count atoms when you balance equations, talk about the atoms of an element, and describe what an atom gains, loses or shares in a reaction.
Examples
A water molecule contains two hydrogen atoms and one oxygen atom.
Count the atoms on each side before you say the equation is balanced.
Usage note
English stresses the first syllable: AT-om. In the adjective 'atomic' the stress moves to the second syllable: a-TOM-ic.
Common phrases
carbon atom · hydrogen atom · atoms of an element · central atom · atomic structure
A pure substance made of only one kind of atom, all with the same number of protons. It cannot be broken down into simpler substances by chemical reactions.
Where you use it
Used constantly with the periodic table. You say an element has a symbol, belongs to a group and forms compounds. Many element names in English differ from Turkish, and some symbols come from Latin.
Examples
Sodium is a very reactive element, so we store it under oil.
Which element has the symbol K? Potassium, from the Latin name kalium.
Common phrases
chemical element · element symbol · trace element · main-group element
A chart that arranges all known elements in order of atomic number, in rows called periods and columns called groups. Elements in the same group behave in similar ways.
Where you use it
Students and chemists use it daily to find symbols, atomic masses and trends. You say an element is 'in group 1' or 'in period 3', and describe trends 'across a period' (left to right) and 'down a group' (top to bottom).
Examples
Atomic radius decreases across a period of the periodic table.
Check the periodic table on the wall for the atomic mass of chlorine.
Common phrases
on the periodic table · group of the periodic table · periodic trend · across a period · down a group
A tiny particle with a negative charge that moves around the nucleus of an atom. Chemical bonds and reactions are mostly about how these particles are shared or transferred.
Where you use it
Found everywhere in chemistry: atoms gain, lose, share, donate or accept electrons. In organic and inorganic chemistry you also hear about lone pairs, unpaired electrons and electron density.
Examples
Sodium loses one electron to form the Na⁺ ion.
In water, the oxygen atom has two lone pairs of electrons.
Common phrases
lose an electron · gain an electron · share electrons · lone pair of electrons · electron density
An atom or group of atoms that carries an electric charge because it has gained or lost electrons. Positive ones are cations and negative ones are anions.
Where you use it
Used in inorganic chemistry, solutions and analysis. Salts dissolve into ions, ions carry current in solution, and chemists talk about metal ions, spectator ions and polyatomic ions such as sulfate.
Examples
When sodium chloride dissolves, it splits into sodium and chloride ions.
Write the net ionic equation and leave out the spectator ions.
Common phrases
metal ion · spectator ion · polyatomic ion · hydroxide ion · ion concentration
The number of protons in the nucleus of an atom. It identifies the element: every carbon atom has 6 protons and every oxygen atom has 8.
Where you use it
Used with the periodic table, which lists the elements in order of increasing atomic number. Its symbol is Z. Don't mix it up with the mass number (protons plus neutrons), written A.
Examples
Iron has an atomic number of 26, so its atoms have 26 protons.
Elements in the periodic table are arranged by increasing atomic number.
Common phrases
atomic number of · increasing atomic number · same atomic number · mass number
One of two or more forms of the same element whose atoms have the same number of protons but a different number of neutrons, such as carbon-12 and carbon-14.
Where you use it
Used in analytical, nuclear and environmental chemistry. Isotopes are stable or radioactive; chemists talk about isotope ratios, isotopic labeling and deuterium, the heavy isotope of hydrogen.
Examples
Chlorine has two stable isotopes, chlorine-35 and chlorine-37.
The mass spectrum clearly shows the isotope pattern of the two bromine atoms.
Common phrases
stable isotope · radioactive isotope · isotope ratio · heavy isotope · isotopic labeling
An electron in the outermost shell of an atom. These outer electrons take part in bonding and largely decide how an element reacts.
Where you use it
Used when you draw Lewis structures and explain why elements bond the way they do. Elements in the same main group have the same number of valence electrons: carbon has four, the halogens have seven.
Examples
Nitrogen has five valence electrons and usually forms three bonds.
Count the valence electrons before you draw the Lewis structure.
Common phrases
number of valence electrons · share valence electrons · valence shell · outer electrons
The way an atom's electrons are arranged in shells and orbitals, written for example as 1s² 2s² 2p⁶ 3s¹ for sodium.
Where you use it
Used to explain the periodic table, ion charges and bonding. You write the configuration, often in short form with a noble gas core, such as [Ne] 3s¹. Read '2p⁶' aloud as 'two p six'.
Examples
Write the electron configuration of chlorine and of the chloride ion.
Copper has an unusual electron configuration: [Ar] 3d¹⁰ 4s¹.
Common phrases
write the electron configuration · ground-state electron configuration · noble gas configuration · electron configuration of
A region around the nucleus where an electron is likely to be found. Each one holds at most two electrons, and the main types are labeled s, p, d and f.
Where you use it
Used in atomic structure, bonding theory and organic chemistry. You talk about filling orbitals, orbital overlap, hybrid orbitals such as sp³, and empty or half-filled orbitals.
Examples
Each p orbital can hold two electrons with opposite spins.
The carbon atom in methane uses four sp³ hybrid orbitals.
Usage note
An orbital is not a fixed path like a planet's orbit; it describes where the electron is likely to be.
Common phrases
p orbital · hybrid orbital · orbital overlap · fill an orbital · molecular orbital
A metal from the central block of the periodic table, usually taken as groups 3 to 12, such as iron, copper, nickel and platinum. Many form colored compounds and have several oxidation states.
Where you use it
Used in inorganic chemistry and catalysis. You speak of transition metal complexes, transition metal catalysts and d-block elements. Their colored solutions are a familiar sight in teaching labs.
Examples
Many transition metal ions give colored solutions, for example blue Cu²⁺.
Palladium is a transition metal widely used as a catalyst.
Common phrases
transition metal complex · transition metal catalyst · d-block element · transition metal ion
An ion with a positive charge, formed when an atom or group of atoms loses electrons. Na⁺, Ca²⁺ and NH₄⁺ are examples.
Where you use it
Used in inorganic, analytical and electrochemistry. Metals usually form cations, and in electrolysis cations move toward the cathode. In the name of a salt the cation comes first: sodium chloride.
Examples
Group 2 metals form cations with a 2+ charge.
The flame test identifies the metal cation in the salt.
Usage note
Pronounced CAT-eye-on, like 'cat' + 'ion'. It does not rhyme with words ending in '-tion'.
Common phrases
metal cation · form a cation · cation exchange · monovalent cation
An ion with a negative charge, formed when an atom or group of atoms gains electrons. Cl⁻, OH⁻ and SO₄²⁻ are examples.
Where you use it
Used together with 'cation'. Nonmetals usually form anions, whose names often end in '-ide' (chloride, oxide), or in '-ate' and '-ite' when they contain oxygen (sulfate, nitrite). In electrolysis anions move toward the anode.
Examples
Silver nitrate is used to test for halide anions such as chloride.
Sulfate is a polyatomic anion with a 2− charge.
Usage note
Pronounced AN-eye-on, with the stress on the first syllable.
Common phrases
polyatomic anion · halide anion · anion exchange · form an anion
A substance made of two or more different elements chemically joined in a fixed ratio. Water (H₂O) and table salt (NaCl) are common examples.
Where you use it
A core word in every course and lab. Elements combine or react to form a compound, and chemists synthesize, isolate, purify and name compounds. Do not confuse it with a mixture, whose parts are not chemically bonded.
Examples
The new compound was purified by column chromatography and characterized by NMR.
Iron and sulfur form a compound when you heat them together.
Common phrases
chemical compound · ionic compound · form a compound · synthesize a compound · unknown compound
A group of two or more atoms held together by covalent bonds. It is the smallest particle of a substance such as water or oxygen gas that still has that substance's chemical properties.
Where you use it
Used whenever you describe covalent substances: the shape of a molecule, polar and nonpolar molecules, large molecules such as proteins. Ionic solids like NaCl are not usually called molecules; chemists speak of formula units instead.
Examples
Carbon dioxide is a linear molecule, so its bond dipoles cancel out.
One molecule of glucose contains six carbon atoms.
Usage note
Stress the first syllable: MOL-e-cule. The adjective 'molecular' is stressed on the second: mo-LEC-u-lar.
Common phrases
polar molecule · water molecule · small molecule · shape of a molecule · diatomic molecule
A chemical bond in which two atoms share one or more pairs of electrons. It usually forms between nonmetal atoms, as in H₂, H₂O and CH₄.
Where you use it
A key term in general and organic chemistry. Covalent bonds can be single, double or triple, and polar or nonpolar. You form, break or draw them; in a structural formula each line usually stands for one shared pair.
Examples
Carbon forms four covalent bonds in most organic molecules.
In a double covalent bond, the two atoms share two pairs of electrons.
Common phrases
single covalent bond · polar covalent bond · form a covalent bond · break a covalent bond
The strong attraction between positive and negative ions that forms when one atom, usually a metal, transfers electrons to another, usually a nonmetal. Sodium chloride is the classic case.
Where you use it
Taught alongside covalent bonding. Ionic compounds have high melting points and conduct electricity when molten or dissolved in water. In an ionic bond electrons are transferred, not shared.
Examples
Magnesium oxide has very strong ionic bonds, so it melts at about 2,800 °C.
Is the bond in NaCl ionic or covalent?
Common phrases
ionic bonding · ionic compound · form an ionic bond · strong ionic bonds
A measure of how strongly an atom pulls shared electrons toward itself in a bond. Fluorine has the highest value, about 4.0 on the Pauling scale.
Where you use it
Used to predict bond polarity and reactivity. It increases across a period and decreases down a group. You compare values and talk about the 'electronegativity difference' between two bonded atoms.
Examples
Oxygen's high electronegativity makes the O–H bond strongly polar.
If the electronegativity difference is large, the bond is mostly ionic.
A fairly strong attraction between a hydrogen atom bonded to N, O or F and a lone pair on a nearby N, O or F atom. It explains why water has such a high boiling point for its size.
Where you use it
Used in physical, organic and biochemistry. It is an intermolecular force, not a true covalent bond. Molecules form or break hydrogen bonds, and the shapes of DNA and proteins depend on hydrogen bonding.
Examples
Ethanol mixes with water because it can form hydrogen bonds with it.
Hydrogen bonding between water molecules gives ice its open structure.
Common phrases
form hydrogen bonds · hydrogen bonding · hydrogen bond donor · hydrogen bond acceptor
Attractions between separate molecules, such as hydrogen bonds, dipole–dipole forces and London dispersion forces. They are much weaker than the bonds inside molecules.
Where you use it
Used to explain boiling points, solubility and the states of matter. You compare them and say they are strong or weak; teachers often shorten the term to IMFs. 'Intramolecular' means inside one molecule.
Examples
Stronger intermolecular forces mean a higher boiling point.
Which intermolecular forces are present in liquid ammonia?
Usage note
inter- means 'between' and intra- means 'within'. Mixing up intermolecular and intramolecular changes the meaning completely.
Describes a bond or molecule in which electrons are shared unevenly, so that one end is slightly negative and the other slightly positive. Water is a typical example.
Where you use it
Used to predict solubility, boiling points and behavior in chromatography. The opposite is 'nonpolar' (also 'non-polar'). Water, methanol and DMSO are polar solvents; hexane and toluene are nonpolar.
Examples
The more polar compound moves more slowly up the silica plate.
Carbon dioxide has polar bonds, but the molecule itself is nonpolar.
A drawing of a molecule or ion that shows its atoms, the bonds between them as lines, and the lone pairs of valence electrons as dots.
Where you use it
Taught early in general chemistry. You draw a Lewis structure, check that each atom has an octet and calculate formal charges. It is also called a Lewis dot structure or an electron dot diagram.
Examples
Draw the Lewis structure of carbon dioxide and show both double bonds.
In the Lewis structure of ammonia, nitrogen has one lone pair.
Common phrases
draw a Lewis structure · Lewis dot structure · octet rule · formal charge
A process in which substances change into new substances with different properties, as bonds between atoms break and new bonds form.
Where you use it
In lectures and labs people often just say 'the reaction'. Reactions take place, occur or go to completion; you set up, run, monitor and quench a reaction, then work it up. Common types are combustion, precipitation, redox and acid–base reactions.
Examples
Bubbles, a color change or a rise in temperature can show that a chemical reaction has taken place.
We monitored the chemical reaction by TLC every thirty minutes.
Common phrases
carry out a reaction · the reaction takes place · side reaction · reaction conditions · monitor a reaction
A short written description of a reaction using formulas and symbols, with the reactants on the left, an arrow in the middle and the products on the right.
Where you use it
Used in exams, lab reports and papers. You write and balance an equation and add state symbols: (s), (l), (g) and (aq). Read the arrow aloud as 'gives', 'forms' or 'reacts to form'.
Examples
Write the chemical equation for the combustion of methane, including state symbols.
The chemical equation tells you that two moles of hydrogen react with one mole of oxygen.
Common phrases
write a chemical equation · balance a chemical equation · ionic equation · word equation · state symbols
A starting substance that is used up or changed in a chemical reaction. In an equation, these substances are written to the left of the arrow.
Where you use it
Used in textbooks and reports; in synthesis labs people often say 'starting material' or 'reagent' instead. You mix, add or consume reactants, and the one left over at the end is the 'reactant in excess'.
Examples
In this reaction, both reactants are colorless but the product is bright yellow.
The reactants must be completely dry before you mix them.
Common phrases
reactant in excess · consume a reactant · reactants and products · starting material
A substance formed in a chemical reaction. In an equation, these new substances are written to the right of the arrow.
Where you use it
Used everywhere in synthesis. You isolate, purify, dry and characterize the product and report its yield. The one you want is the 'desired' or 'main' product; unwanted ones are side products or by-products.
Examples
The crude product was recrystallized from hot ethanol.
Is the white solid the product or unreacted starting material?
Common phrases
crude product · main product · side product · isolate the product · purify the product
A chemical equation with the same number of atoms of each element on both sides and the same total charge, so that mass is conserved.
Where you use it
Needed before any calculation with amounts. You balance an equation by changing the coefficients (the numbers in front of the formulas), never the subscripts. 'Is the equation balanced?' is a common exam and lab question.
Examples
The balanced equation is 2H₂ + O₂ → 2H₂O.
Use the mole ratio from the balanced equation to find the mass of product.
Common phrases
balance an equation · balanced chemical equation · coefficients · mole ratio
An insoluble solid that forms when two solutions are mixed and separates out of the liquid. As a verb, the word means to form such a solid.
Where you use it
Common in inorganic and analytical work. A precipitate forms, settles, is filtered off and washed; as a verb, a salt 'precipitates' or 'precipitates out'. Precipitates are often described by color: a white precipitate of silver chloride.
Examples
A white precipitate formed as soon as we added silver nitrate.
Filter off the precipitate and wash it with cold water.
Usage note
The noun ends in /ət/ (pre-CIP-i-tət), the verb in /eɪt/ (pre-CIP-i-tate). The weather word 'precipitation' (rain or snow) comes from the same root.
Common phrases
white precipitate · form a precipitate · filter off the precipitate · precipitate out
A change in which a substance loses electrons, so its oxidation number goes up. It often involves gaining oxygen or losing hydrogen.
Where you use it
Always paired with reduction in redox chemistry. Metals undergo oxidation when they corrode, and in organic chemistry an alcohol is oxidized to an aldehyde, ketone or acid. Students remember 'OIL RIG': oxidation is loss, reduction is gain of electrons.
Examples
The oxidation of iron in moist air produces rust.
In this step, oxidation of the secondary alcohol gives the ketone.
Common phrases
oxidation state · oxidation number · undergo oxidation · oxidation of · oxidizing agent
A change in which a substance gains electrons, so its oxidation number goes down. It often involves losing oxygen or gaining hydrogen.
Where you use it
The partner of oxidation in every redox reaction. In metallurgy ores are reduced to metals; in organic labs ketones are reduced to alcohols with reagents such as sodium borohydride. The substance that causes it is the reducing agent.
Examples
Reduction of copper oxide with hydrogen gives copper metal and water.
The reduction of the ketone was complete after one hour.
Usage note
In everyday English 'reduction' means a decrease, such as a price reduction. In chemistry it means gaining electrons: the oxidation number is what gets smaller.
A reaction in which electrons move from one substance to another, so that one substance is oxidized while another is reduced at the same time.
Where you use it
Covers combustion, corrosion, batteries and many titrations. You balance redox reactions with half-equations and identify the oxidizing and reducing agents. 'Redox' is short for reduction–oxidation.
Examples
Identify which species is oxidized and which is reduced in this redox reaction.
A battery produces electricity from a controlled redox reaction.
The SI unit for amount of substance. One of these units contains about 6.022 × 10²³ particles, which lets chemists count atoms and molecules by weighing them.
Where you use it
The basic counting unit in every calculation; its symbol is mol. You convert grams to moles, calculate the number of moles and work in millimoles (mmol) in the lab. The substance follows 'moles of': moles of NaOH.
Examples
How many moles of NaOH do we need to neutralize the acid?
First convert the mass of the sample into moles.
Usage note
The same word also means a small animal and a dark spot on the skin; in chemistry it is always the unit.
Common phrases
number of moles · moles of · convert to moles · mole ratio · per mole
The mass of one mole of a substance, usually given in grams per mole (g/mol). For water it is about 18.02 g/mol.
Where you use it
Used in almost every lab calculation to switch between grams and moles. You calculate, look up or check the molar mass; bottle labels and older texts often give the same number as 'molecular weight' (MW) or 'formula weight' (FW).
Examples
The molar mass of sodium chloride is 58.44 g/mol, so 5.844 g is 0.1 mol.
Use the molar mass on the bottle label, not a rounded value.
Usage note
English uses a decimal point (58.44), Turkish a decimal comma (58,44). A comma in an English report can be read as a thousands separator.
Common phrases
calculate the molar mass · molar mass of · grams per mole · look up the molar mass
The calculation of the amounts of reactants and products in a reaction, using the mole ratios from the balanced equation.
Where you use it
A core topic in general chemistry and a daily tool in synthesis. You solve stoichiometry problems and say reagents are used 'in stoichiometric amounts' or 'in excess'. In procedures, chemists write 'equiv' for equivalents.
Examples
The stoichiometry tells us we need two moles of hydrogen for every mole of oxygen.
Check the stoichiometry before you scale up the reaction.
Usage note
Pronounced stoy-kee-OM-e-tree, with the stress on 'om'.
Common phrases
reaction stoichiometry · stoichiometric amount · stoichiometry problem · mole ratio
The reactant that runs out first in a reaction. It decides the maximum amount of product that can form; the other reactants are left over in excess.
Where you use it
Used in stoichiometry problems and when planning a synthesis. You identify the limiting reagent and base the theoretical yield on it. 'Limiting reactant' means the same thing.
Examples
Calculate the moles of each reactant to find the limiting reagent.
The amine is the limiting reagent, so base the yield on it.
Common phrases
identify the limiting reagent · reagent in excess · limiting reactant · based on the limiting reagent
The amount of product actually obtained, divided by the maximum possible (theoretical) amount and multiplied by 100. It shows how efficient a reaction was.
Where you use it
Reported for every synthesis and in lab reports. You calculate it from the actual and theoretical yield; papers often just say 'in 85% yield'. British English also says 'percentage yield'.
Examples
We got 4.2 g of product from a theoretical 5.0 g, so the percent yield is 84%.
A percent yield above 100% usually means the product is still wet.
Common phrases
calculate the percent yield · theoretical yield · actual yield · in high yield · low yield
The number of particles in one mole of a substance, about 6.022 × 10²³. Strictly speaking, the Avogadro constant has the unit per mole (mol⁻¹).
Where you use it
Used to convert between moles and numbers of atoms, ions or molecules. Its symbol is N_A. Since 2019 its value has been fixed at exactly 6.02214076 × 10²³ mol⁻¹, and this number defines the mole.
Examples
Multiply the number of moles by Avogadro's number to get the number of molecules.
One mole of carbon-12 contains Avogadro's number of atoms and has a mass of about 12 g.
Usage note
Remember the possessive in 'Avogadro's number'; the official name 'the Avogadro constant' has no 's.
Common phrases
Avogadro constant · multiply by Avogadro's number · number of particles
The simplest whole-number ratio of the atoms of each element in a compound. Glucose is C₆H₁₂O₆, but its simplest ratio is CH₂O.
Where you use it
Calculated from elemental analysis or percent composition data. You determine or work out the empirical formula, then use the molar mass to find the molecular formula.
Examples
The elemental analysis gives an empirical formula of C₂H₅O.
Use the molar mass to go from the empirical formula to the molecular formula.
Common phrases
determine the empirical formula · molecular formula · percent composition · elemental analysis
A substance that releases hydrogen ions (H⁺) in water or, more generally, donates protons. Its water solutions have a pH below 7 and turn blue litmus paper red.
Where you use it
A basic word in every chemistry course. Acids are strong or weak, concentrated or dilute, and react with bases, metals and carbonates. Common lab acids are hydrochloric, sulfuric, nitric and acetic acid.
Examples
Always add acid to water, never water to acid.
Hydrochloric acid reacts with zinc to give hydrogen gas.
A substance that accepts protons (H⁺) or releases hydroxide ions (OH⁻) in water. Its solutions have a pH above 7 and turn red litmus paper blue.
Where you use it
Used together with 'acid' in acid–base chemistry. Common lab bases are sodium hydroxide, potassium hydroxide and ammonia. A base that dissolves in water is called an alkali, and its solution is described as alkaline or basic.
Examples
Sodium hydroxide is a strong base, so wear goggles when you handle it.
Add the base dropwise until the solution turns pink.
Usage note
'Base' also means the bottom of something, and in biology a DNA base. In chemistry 'basic' often means 'having a pH above 7', not just 'simple'.
Common phrases
strong base · weak base · conjugate base · add base · acid–base titration
A scale, usually from 0 to 14, that shows how acidic or basic a solution is. Below 7 is acidic, 7 is neutral at 25 °C and above 7 is basic; it equals −log[H⁺].
Where you use it
Used in every lab: you measure, check, adjust, raise or lower the pH with a pH meter or pH paper. Write it with a small p and a capital H, and say the letters: 'pee-aitch'.
Examples
Adjust the pH of the buffer to 7.4 with dilute sodium hydroxide.
The pH dropped from 6 to 3, so the solution is now a thousand times more acidic.
Usage note
Many Turkish speakers say 'pe-ha', the German way. In English, say 'pee-aitch'.
Common phrases
pH meter · pH paper · adjust the pH · low pH · pH value
The reaction between an acid and a base that produces a salt and water and brings the pH closer to 7.
Where you use it
Used in titrations, waste treatment and spill clean-up. You neutralize an acid with a base or the other way round, and the reaction is usually exothermic. The British spelling is 'neutralisation'.
Examples
The neutralization of hydrochloric acid with sodium hydroxide gives sodium chloride and water.
Check the pH after neutralization to make sure the waste is close to neutral.
Common phrases
neutralization reaction · heat of neutralization · acid–base neutralization · neutralize an acid
An ionic compound made of positive and negative ions, usually formed when an acid reacts with a base. Sodium chloride is the best known, but there are thousands of others.
Where you use it
In chemistry 'salt' is a whole family of compounds, not just table salt. You hear about sodium salts, the hydrochloride salts of drugs and salt formation. Names come from the ions: copper(II) sulfate, potassium nitrate.
Examples
Copper(II) sulfate is a blue salt that dissolves easily in water.
The drug is sold as its hydrochloride salt because it is more stable and more soluble.
Common phrases
sodium salt · form a salt · hydrochloride salt · insoluble salt · salt solution
A solution that resists changes in pH when small amounts of acid or base are added. It usually contains a weak acid and its conjugate base, such as acetic acid and sodium acetate.
Where you use it
Essential in biochemistry, analysis and instrument calibration. You prepare or make up a buffer and adjust its pH; people speak of 'a phosphate buffer at pH 7.4' and of buffer capacity. pH meters are calibrated with standard buffers.
Examples
Calibrate the pH meter with the pH 4 and pH 7 buffers.
Blood is a natural buffer system that keeps the pH near 7.4.
An acid that ionizes almost completely in water, releasing nearly all of its hydrogen ions. Hydrochloric, nitric and sulfuric acid are common examples.
Where you use it
Contrasted with weak acids such as acetic acid, which ionize only partly. 'Strong' describes ionization, not concentration: you can have a dilute strong acid or a concentrated weak acid.
Examples
A 0.01 M solution of a strong acid like HCl has a pH of 2.
Titrating a strong acid with a strong base gives a sharp pH jump around 7.
Usage note
Turkish learners sometimes translate 'derişik asit' as 'strong acid'. For high concentration the right word is 'concentrated'.
Common phrases
strong acid · weak acid · strong base · strong acid–strong base titration
A substance that changes color at a certain pH or at the end of a reaction, used to show when a titration is complete. Phenolphthalein and methyl orange are common examples.
Where you use it
Used in titrations and quick pH checks. You add a few drops of indicator and watch for the color change. Phenolphthalein is colorless in acid and pink in base; universal indicator shows a range of colors.
Examples
Add two or three drops of phenolphthalein indicator to the flask.
Choose an indicator that changes color close to the equivalence point.
A uniform mixture in which one substance (the solute) is completely dissolved in another (the solvent). Salt water and sugar dissolved in tea are everyday examples.
Where you use it
One of the most used words in the lab. You prepare, make up, dilute, stir and filter solutions; a solution can be aqueous, saturated, concentrated or dilute. Context tells you whether 'solution' means the mixture or the answer to a problem.
Examples
Prepare 250 mL of a 0.1 M sodium hydroxide solution.
The solution turned blue when we added the copper sulfate.
Usage note
Turkish has two words here: 'çözelti' (the mixture) and 'çözüm' (the answer). English uses 'solution' for both.
The substance, usually a liquid, that dissolves another substance to form a solution. Water is the most common one; ethanol, acetone and hexane are widely used organic ones.
Where you use it
Used daily in synthesis and analysis. You choose, add, evaporate, remove or recover a solvent, and chemists distinguish polar from nonpolar solvents. 'Dry solvent' means water-free, and used solvent goes into solvent waste.
Examples
Remove the solvent on the rotary evaporator before you weigh the product.
Water is a poor solvent for oils because it is highly polar.
The substance that gets dissolved in a solvent to make a solution. In salt water, the salt plays this role and the water is the solvent.
Where you use it
Mostly used in textbooks, exams and calculations, for example when you calculate the moles of solute or describe solute–solvent interactions. In the lab people usually name the actual compound instead.
Examples
Molarity is the number of moles of solute per liter of solution.
The solute crystallized out when the solution cooled.
Usage note
Do not confuse 'solute' (the dissolved substance) with 'solution' (the whole mixture). It also looks like 'salute', which has nothing to do with chemistry.
The amount of a substance in a given volume of solution or mixture, for example in moles per liter (mol/L), grams per liter or parts per million (ppm).
Where you use it
Used in every lab, report and method. You determine, measure, increase or lower the concentration. Square brackets mean concentration in equations, so [H⁺] is read 'the concentration of H plus'.
Examples
The concentration of the stock solution is 1.0 mol/L.
Increasing the concentration of the reactants speeds up the reaction.
Common phrases
final concentration · high concentration · determine the concentration · concentration of · unknown concentration
A measure of concentration: the number of moles of solute in one liter of solution. Its unit is mol/L, written M and read 'molar'.
Where you use it
The standard way to state concentration in the lab; '0.5 M' is read 'zero point five molar'. It is per liter of solution, not per liter of solvent. Molality (moles per kilogram of solvent) is a different quantity.
Examples
What is the molarity of a solution with 4.0 g of NaOH in 500 mL?
Check the molarity on the label before you use the stock solution.
Common phrases
calculate the molarity · molarity of · final molarity · 0.1 M solution
To make a solution weaker by adding more solvent, usually water. As an adjective, the word describes a solution with a low concentration.
Where you use it
Used daily when you prepare solutions. You dilute a sample tenfold or '1 in 10', dilute 'to the mark' or 'with water', and calculate with C₁V₁ = C₂V₂. The noun is 'dilution'; the opposite adjective is 'concentrated'.
Examples
Dilute 10 mL of the stock solution to 100 mL with distilled water.
We used dilute hydrochloric acid to clean the electrodes.
Usage note
'Dilute' (low concentration) is not the same as 'weak' (only partly ionized). A dilute strong acid is still a strong acid.
Common phrases
dilute with water · dilute to the mark · dilute tenfold · dilute acid · serial dilution
The maximum amount of a substance that can dissolve in a given amount of solvent at a certain temperature, often given in grams per 100 g of water.
Where you use it
Important when you choose solvents, recrystallize or predict precipitates. Solubility rises or falls with temperature, and compounds are described as soluble, slightly soluble or insoluble. The rule of thumb is 'like dissolves like'.
Examples
The solubility of potassium nitrate in water rises sharply with temperature.
Because of its low solubility in water, the product precipitates when you add water.
Common phrases
solubility in water · low solubility · solubility curve · solubility product
Describes a solution in which water is the solvent. In equations it is shown by the state symbol (aq), as in NaCl(aq).
Where you use it
Very common in equations, procedures and extractions. You speak of an aqueous solution, the aqueous layer in a separating funnel and an aqueous work-up. In an extraction the other layer is the organic layer.
Examples
Wash the organic layer twice with saturated aqueous sodium bicarbonate.
Which layer is aqueous? Add a drop of water and see where it goes.
Usage note
Pronounced AY-kwee-us; the first syllable rhymes with 'day'.
A compound built mainly from carbon atoms bonded to hydrogen, often with oxygen, nitrogen or other elements. Fuels, plastics, drugs and most molecules of living things belong here.
Where you use it
The basic subject of organic chemistry courses and synthesis labs. Simple carbon compounds such as carbon dioxide, carbonates and cyanides are traditionally treated as inorganic. 'Volatile organic compounds' (VOCs) is a common term in environmental work.
Examples
Most organic compounds burn in air to give carbon dioxide and water.
Ethanol is an organic compound that mixes with water in any ratio.
Usage note
In everyday English 'organic' food is grown without synthetic chemicals; in chemistry 'organic' only means carbon-based.
A compound made of only carbon and hydrogen. Methane, propane, ethylene and benzene are examples, and crude oil is mostly a mixture of them.
Where you use it
Used in organic chemistry, fuels and the petrochemical industry. Hydrocarbons are saturated (only single bonds) or unsaturated (double or triple bonds), and aliphatic or aromatic. They burn well and are generally insoluble in water.
Examples
Hexane is a hydrocarbon solvent often used to extract oils.
Complete combustion of a hydrocarbon gives only carbon dioxide and water.
A specific group of atoms within a molecule, such as –OH or –COOH, that gives the molecule its typical reactions. Compounds with the same group react in similar ways.
Where you use it
Central to organic chemistry: you identify, protect, convert or introduce a functional group. Families such as alcohols, aldehydes, ketones, carboxylic acids, amines and esters are defined by them, and IR spectra help to identify them.
Examples
The broad peak near 3300 cm⁻¹ tells us the molecule has an –OH functional group.
Name the functional groups in aspirin.
Common phrases
identify a functional group · protect a functional group · carbonyl group · hydroxyl group
One of two or more compounds that have the same molecular formula but a different arrangement of atoms, and so have different properties. Butane and isobutane are an example.
Where you use it
Used in organic chemistry and drug development. The main types are structural isomers and stereoisomers, which include enantiomers. You draw, separate or identify isomers; turning one into another is isomerization.
Examples
Draw all the structural isomers of C₅H₁₂.
The two isomers have the same molecular formula but very different boiling points.
A saturated hydrocarbon with only single bonds between its carbon atoms and the general formula CₙH₂ₙ₊₂. Methane, ethane, propane and butane are the simplest ones.
Where you use it
Usually the first family you study in organic chemistry, because naming rules start here. Alkanes are fairly unreactive, burn well and make up most of natural gas and many fuels. Their names end in '-ane'.
Examples
Name this branched alkane using IUPAC rules.
Hexane is a liquid alkane often used as a nonpolar solvent.
Usage note
Alkane ends in /eɪn/ ('-ain') and alkene in /iːn/ ('-een'). Say the endings clearly, because they are easy to confuse.
A very large molecule made of many small repeating units called monomers, joined in long chains. Plastics, proteins, starch and DNA are all examples.
Where you use it
Used in materials science, industry and biochemistry. Monomers polymerize to form a polymer, and people talk about synthetic and natural polymers, polymer chains and molecular weight distribution.
Examples
Polyethylene is a polymer made from ethylene monomers.
The polymer becomes brittle after long exposure to UV light.
A hydrocarbon with at least one carbon–carbon double bond. Simple ones have the general formula CₙH₂ₙ, and ethene (ethylene) is the smallest.
Where you use it
Used in organic chemistry and the polymer industry. Alkenes are unsaturated and more reactive than alkanes; they undergo addition reactions and are the starting point for many plastics. Their names end in '-ene'.
Examples
Bromine water loses its orange color when you add an alkene.
Hydrogenation turns the alkene into the corresponding alkane.
Common phrases
addition to an alkene · terminal alkene · cis and trans alkenes · carbon–carbon double bond
An organic compound that contains a flat ring of delocalized electrons, such as a benzene ring. These rings are unusually stable.
Where you use it
Used in organic, pharmaceutical and petrochemical chemistry. Benzene, toluene, phenol and many drugs and dyes are aromatic compounds. They usually undergo substitution rather than addition reactions.
Examples
Aspirin is an aromatic compound with a benzene ring in its structure.
Most aromatic compounds absorb UV light, so they appear as dark spots on a fluorescent TLC plate.
Usage note
'Aromatic' here has nothing to do with smell, even though the name came from the strong odors of the first such compounds studied.
An organic compound formed when a carboxylic acid reacts with an alcohol, with water given off. Many have fruity smells and are used in flavors, perfumes and solvents.
Where you use it
A key functional group in organic labs. Its formation is called esterification and the reverse is hydrolysis. Ethyl acetate, a simple ester, is one of the most used lab solvents. Ester names end in '-ate': methyl benzoate.
Examples
Heating acetic acid with ethanol and a little sulfuric acid gives the ester ethyl acetate.
The ester smelled strongly of bananas.
Common phrases
ester bond · ester hydrolysis · form an ester · methyl ester
A substance that speeds up a chemical reaction without being used up. It works by offering a different pathway with a lower activation energy.
Where you use it
Used in synthesis, industry and biochemistry. You add, use, recover or poison a catalyst, and say a reaction is 'catalyzed by' something. Enzymes are biological catalysts; palladium and platinum are common metal ones.
Examples
We used 5 mol% of a palladium catalyst for the coupling reaction.
A catalyst is not used up, so you can recover it after the reaction.
Usage note
A catalyst does not change the position of equilibrium; it only helps the system reach equilibrium faster.
Common phrases
add a catalyst · acid catalyst · metal catalyst · catalyst loading · in the presence of a catalyst
Describes a reaction or process that releases heat to the surroundings, so the temperature rises. Its enthalpy change (ΔH) is negative.
Where you use it
Important for safety and energy calculations. Combustion, neutralization and dissolving NaOH in water are exothermic. When a reaction is strongly exothermic, you add reagents slowly or cool the flask.
Examples
The reaction is highly exothermic, so add the acid slowly in an ice bath.
Is dissolving ammonium nitrate in water exothermic or endothermic?
Describes a reaction or process that takes in heat from the surroundings, so the surroundings get colder. Its enthalpy change (ΔH) is positive.
Where you use it
Used with energy diagrams and in thermochemistry. Melting, evaporation, thermal decomposition and photosynthesis are endothermic. Instant cold packs work because dissolving ammonium nitrate is endothermic.
Examples
The decomposition of calcium carbonate is endothermic, so it needs strong heating.
The beaker felt cold, which shows that the dissolving process is endothermic.
Common phrases
endothermic reaction · endothermic process · slightly endothermic
The minimum energy that reacting particles need to collide successfully and start a reaction. Catalysts work by lowering it.
Where you use it
Used in kinetics and on energy diagrams. You calculate it from rate data with the Arrhenius equation; its symbol is Eₐ, usually in kJ/mol. A high activation energy means a slow reaction at room temperature.
Examples
The catalyst lowers the activation energy, so the reaction runs at room temperature.
Determine the activation energy from a plot of ln k against 1/T.
Common phrases
lower the activation energy · high activation energy · energy barrier · Arrhenius equation
How fast reactants are used up or products are formed, usually measured as a change in concentration per unit time, for example in mol/L per second.
Where you use it
Used in kinetics and when planning experiments. Temperature, concentration, surface area and catalysts increase or decrease the reaction rate. You measure, follow or compare rates; 'rate of reaction' is also common.
Examples
Raising the temperature by 10 °C roughly doubled the reaction rate.
We followed the reaction rate by measuring the volume of gas every minute.
Common phrases
increase the reaction rate · rate of reaction · initial rate · rate constant · rate law
The state of a reversible reaction in which the forward and reverse reactions run at the same rate, so the amounts of reactants and products stay constant.
Where you use it
Used in general, physical and analytical chemistry. A system reaches or is at equilibrium, and the equilibrium position shifts to the left or right. It is dynamic, because both reactions keep going. The double arrow ⇌ shows it.
Examples
At chemical equilibrium, the concentrations no longer change, but both reactions continue.
The esterification reaches chemical equilibrium after several hours.
Usage note
Turkish 'denge' (equilibrium) and 'denk' (balanced, as in a balanced equation) are easy to mix up in translation; they are different ideas.
Common phrases
reach equilibrium · at equilibrium · equilibrium position · shift the equilibrium · dynamic equilibrium
The heat content of a system at constant pressure. Chemists usually measure its change, ΔH, which shows how much heat a reaction gives out or takes in.
Where you use it
Used in thermochemistry and physical chemistry. You calculate the enthalpy change of a reaction, use standard enthalpies of formation or combustion, and apply Hess's law. Values are given in kJ/mol, and ΔH is read 'delta H'.
Examples
The enthalpy change for the combustion of methane is about −890 kJ/mol.
Use Hess's law to calculate the enthalpy of formation.
Usage note
Stress the first syllable: EN-thal-py. Don't confuse it with 'entropy' (a measure of disorder), which sounds similar.
Common phrases
enthalpy change · standard enthalpy of formation · enthalpy of combustion · Hess's law
The rule that when a system at equilibrium is disturbed by a change in concentration, pressure or temperature, the equilibrium shifts in the direction that reduces the effect of the change.
Where you use it
Used to predict how to get more product from equilibrium reactions, such as the Haber process for ammonia. You apply the principle and say the equilibrium 'shifts to the right' (toward products) or 'to the left'.
Examples
By Le Chatelier's principle, removing water will push the esterification toward the products.
Use Le Chatelier's principle to explain why high pressure favors ammonia formation.
Usage note
The name is French, so the final r is silent: roughly 'luh sha-TEL-yay'.
Common phrases
apply Le Chatelier's principle · shift the equilibrium · according to Le Chatelier's principle
A number, K, that relates the concentrations or pressures of the products to those of the reactants when a reaction is at equilibrium. A large value means the products are favored.
Where you use it
Used in general, analytical and physical chemistry. You write the expression for K, calculate it and compare it with the reaction quotient Q. Kc uses concentrations and Kp partial pressures; Ka and Kb describe acid and base strength. K changes only with temperature.
Examples
Write the equilibrium constant expression for the formation of ammonia.
Because the equilibrium constant is very small, almost no product forms.
Common phrases
equilibrium constant expression · Kc and Kp · acid dissociation constant · large equilibrium constant
A simple cylindrical glass or plastic container with a flat bottom and a small spout, used for mixing, heating and holding liquids. Its volume marks are only approximate.
Where you use it
Used every day in teaching and research labs. You pour into, stir in, heat or rinse a beaker. It is not for accurate measuring: use a graduated cylinder, pipette or volumetric flask for that.
Examples
Dissolve the solid in about 50 mL of water in a 100 mL beaker.
Don't use the beaker markings to measure volumes for your titration.
Common phrases
glass beaker · 250 mL beaker · pour into a beaker · rinse the beaker
A thin glass or plastic tube used to measure and transfer a precise volume of liquid. Volumetric types deliver one fixed volume; micropipettes handle microliters.
Where you use it
Used constantly in analytical and biochemistry labs, also as a verb: 'pipette 10 mL of the sample'. You use a pipette filler or bulb, change the tip and never pipette by mouth. US texts sometimes spell it 'pipet'.
Examples
Pipette 25 mL of the acid into a clean conical flask.
Never use your mouth to fill a pipette; use a pipette filler.
A long, graduated glass tube with a tap (stopcock) at the bottom, used to add a liquid gradually and measure exactly how much was added, mainly in titrations.
Where you use it
A standard titration tool. You rinse, fill, clamp and read a burette, record the initial and final readings, and read it at eye level at the bottom of the meniscus. The US spelling is 'buret'.
Examples
Rinse the burette with a little of the NaOH solution before filling it.
The burette reading was 23.45 mL at the endpoint.
Common phrases
burette reading · fill the burette · burette stand · burette tap · 50 mL burette
A pear-shaped flask with a long narrow neck and a single line marked on it. Filled to that line, it holds one exact volume, so it is used to prepare standard solutions.
Where you use it
Used in analytical work. You dissolve the solid, 'make up to the mark' with solvent, then stopper the flask and invert it to mix. It is never heated, because heat changes its calibrated volume.
Examples
Transfer the solution to a 250 mL volumetric flask and make up to the mark with water.
Don't heat the volumetric flask; dissolve the solid in a beaker first.
Common phrases
make up to the mark · 250 mL volumetric flask · stopper the flask · Class A volumetric flask
A glass flask with a flat bottom, a cone-shaped body and a narrow neck. Its shape lets you swirl liquids without spilling, so it is the standard flask for titrations.
Where you use it
Used daily in teaching and analytical labs. You swirl, heat, stopper or titrate in an Erlenmeyer flask. British labs usually call it a conical flask; Turkish lab staff often just say 'erlen'.
Examples
Swirl the Erlenmeyer flask gently while you add the titrant.
Put a white tile under the Erlenmeyer flask so you can see the color change.
Usage note
Write Erlenmeyer with a capital E: it is named after the German chemist Emil Erlenmeyer.
Common phrases
250 mL Erlenmeyer flask · conical flask · swirl the flask · stopper the flask
A tall, narrow cylinder with volume markings on its side, used to measure liquids more accurately than a beaker but less accurately than a pipette or burette.
Where you use it
Used for routine volumes, such as solvent for a reaction or for washing. You measure out a liquid, read the volume at the bottom of the meniscus and pour it out. British English calls it a measuring cylinder.
Examples
Measure 50 mL of ethanol with a graduated cylinder.
A graduated cylinder is fine for the washing solvent, but use a pipette for the sample.
Common phrases
100 mL graduated cylinder · measuring cylinder · read the meniscus · measure out
A very sensitive electronic scale, usually reading to 0.1 mg, kept inside a glass draft shield so that air currents do not disturb the reading.
Where you use it
Used to weigh samples and standards accurately. You tare or zero the balance, weigh by difference, close the doors and wait for the reading to settle. In English you 'weigh' a sample; the 'balance' is the instrument.
Examples
Weigh about 0.2 g of the standard accurately on the analytical balance.
Close the doors of the analytical balance before you note the mass.
Usage note
'Weigh' is the verb (tartmak) and 'weight' is the noun (ağırlık). Turkish speakers often write 'weight the sample', which is wrong.
Common phrases
tare the balance · weigh by difference · top-pan balance · four-place balance
A machine that spins samples at high speed so that heavier particles or solids collect at the bottom of the tube and can be separated from the liquid.
Where you use it
Used in analytical, inorganic and biochemistry labs. It is both a noun and a verb: you centrifuge or spin down samples, balance the rotor and set the speed in rpm or g. The clear liquid on top is the supernatant.
Examples
Always balance the tubes in the centrifuge before you start it.
Centrifuge the suspension for five minutes and pour off the supernatant.
Common phrases
centrifuge tube · spin down · balance the centrifuge · centrifuge at 3000 rpm
A method of separating or purifying liquids by boiling a mixture and cooling the vapor so that it condenses and is collected separately. It relies on differences in boiling point.
Where you use it
Used in organic labs and in industry. You set up or carry out a distillation; simple distillation separates liquids with very different boiling points, fractional distillation separates close ones. The collected liquid is the distillate.
Examples
We purified the crude ester by distillation under reduced pressure.
A method of separating a solid from a liquid by passing the mixture through filter paper or another porous material that lets only the liquid through.
Where you use it
One of the most common lab steps. You filter a mixture or filter off a solid, by gravity filtration or by vacuum filtration with a Büchner funnel. The liquid that passes through is the filtrate; the solid left behind is the residue.
Examples
Collect the crystals by vacuum filtration and wash them with cold solvent.
After filtration, the filtrate was clear and colorless.
Common phrases
vacuum filtration · gravity filtration · filter paper · filter off · Büchner funnel
A purification method in which a solid is dissolved in a small amount of hot solvent and left to cool slowly, so that pure crystals form and impurities stay in solution.
Where you use it
The standard way to purify solids in organic labs. You recrystallize a product 'from ethanol', use the minimum amount of hot solvent and check purity by melting point. The British spelling is 'recrystallisation'.
Examples
Recrystallization from hot water gave white needles with a sharp melting point.
Use as little hot solvent as possible during recrystallization.
Common phrases
recrystallize from · purify by recrystallization · recrystallization solvent · melting point
Boiling a reaction mixture for a long time with a condenser fitted on top, so that the vapor condenses and drips back into the flask and no solvent is lost.
Where you use it
Very common in organic synthesis procedures. You heat a mixture 'at reflux' or 'under reflux', reflux it for two hours, or bring it to reflux. The glassware on top is a reflux condenser, usually cooled with running water.
Examples
Heat the mixture under reflux for two hours, then let it cool to room temperature.
Check that water is running through the reflux condenser before you turn on the heat.
Usage note
In medicine 'reflux' means stomach acid flowing back up; in the lab it always means this boiling setup.
Common phrases
heat under reflux · reflux condenser · bring to reflux · reflux overnight
A ventilated cabinet with a sliding glass front that draws fumes away from the user. Work with volatile, toxic or strong-smelling chemicals is done inside it.
Where you use it
Heard in every lab induction. You work in the hood, keep the sash low and check the airflow. Lab staff often just say 'the hood'; British labs call it a fume cupboard.
Examples
Open the bottle of bromine only inside the fume hood.
The fume hood alarm went off because someone left the sash fully open.
Usage note
Turkish 'çeker ocak' is not a cooker: never translate it as 'oven' or 'stove'.
Common phrases
work in the fume hood · fume hood sash · lower the sash · fume hood airflow
A standard document from the supplier that describes a chemical's hazards, safe handling, storage, first aid and disposal. It is usually shortened to SDS.
Where you use it
Required reading before you use a new chemical. You check or consult the SDS, which has 16 standard sections under the GHS. Older documents and many people still say MSDS (material safety data sheet).
Examples
Read the safety data sheet before you use any chemical for the first time.
According to the safety data sheet, this solvent must be stored away from oxidizers.
Common phrases
check the safety data sheet · SDS section · up-to-date SDS · according to the SDS
Short for personal protective equipment: the items you wear to protect yourself from hazards in the lab, such as a lab coat, safety goggles and gloves.
Where you use it
Heard in every safety briefing and written on lab doors. You wear, put on, take off and choose appropriate PPE; nitrile gloves, splash goggles and face shields are typical. It is uncountable: say 'PPE', not 'PPEs'.
Examples
Appropriate PPE must be worn at all times in the lab.
Check which PPE the safety data sheet recommends for this acid.
Common phrases
wear PPE · appropriate PPE · PPE requirements · remove PPE
A small symbol in a red-bordered diamond on a chemical label that warns of a specific danger, such as flammable, toxic, corrosive or harmful to the environment.
Where you use it
Part of the GHS system used around the world, which has nine standard pictograms. You check them on the label and the safety data sheet, together with the signal word ('Danger' or 'Warning') and the hazard statements (H-statements).
Examples
The flame hazard pictogram on the bottle means the solvent is flammable.
New students must learn all nine hazard pictograms before their first lab session.
Common phrases
GHS pictogram · hazard statement · signal word · warning label
Describes a substance that can destroy or badly damage skin, eyes, metals or other materials on contact. Concentrated acids and strong bases are typical examples.
Where you use it
Common on labels, safety data sheets and in safety briefings. Corrosive chemicals are stored low down, in secondary containers, and handled with goggles and gloves. It is also a noun: 'store corrosives separately'.
Examples
Concentrated sulfuric acid is highly corrosive, so wear goggles and a face shield.
Keep corrosive liquids on the lowest shelf, below eye level.
Describes a substance that catches fire easily and burns quickly. Many organic solvents, such as acetone, diethyl ether and ethanol, belong to this group.
Where you use it
Seen on labels, storage cabinets and safety data sheets. Flammable liquids are kept in a flammables cabinet away from heat and sparks, and a low flash point means a higher fire risk. The opposite is 'non-flammable'.
Examples
Diethyl ether is extremely flammable, so there must be no open flames in the room.
Put the flammable solvents back in the cabinet at the end of the day.
Usage note
'Inflammable' means the same as 'flammable', not 'non-flammable'. Safety labels use 'flammable' to avoid exactly this confusion.
Unwanted chemicals and materials contaminated with them, such as used solvents, reaction residues and dirty gloves, that must be collected and disposed of safely.
Where you use it
Every lab has rules for it. You collect, segregate, label and dispose of chemical waste, and halogenated and non-halogenated solvents usually go into separate containers. Nothing goes down the sink unless the lab's rules allow it.
Examples
Pour the chlorinated solvents into the halogenated chemical waste container.
Label every chemical waste bottle with its contents and the date.
Common phrases
chemical waste container · dispose of chemical waste · hazardous waste · waste segregation
An accident in which a chemical is dropped or leaks out of its container. As a verb, the word means to let a liquid or powder fall out by accident.
Where you use it
Part of every lab safety plan. You report, contain, absorb and clean up a spill with a spill kit; trained staff handle small spills, and a large one may mean leaving the lab. The past tense is 'spilled' (US) or 'spilt' (UK).
Examples
If there is an acid spill, cover it with neutralizer from the spill kit.
I spilled some ethanol on the bench; can you pass me the paper towels?
Common phrases
spill kit · clean up a spill · report a spill · chemical spill · contain a spill
A method for finding the unknown concentration of a solution by adding a solution of known concentration from a burette until the reaction between them is just complete.
Where you use it
A classic teaching experiment and a routine quality-control method. You do or run a titration, 'titrate the sample with NaOH', record the burette readings and repeat until two results agree closely.
Examples
We did three titrations and the results agreed within 0.1 mL.
Use phenolphthalein as the indicator for this titration.
Common phrases
acid–base titration · carry out a titration · back titration · titration curve · titrate with
The study of how matter absorbs or emits light and other radiation, used to identify substances and measure their amounts. UV-Vis, IR and NMR are common types.
Where you use it
Used in analytical and organic chemistry to find structures and concentrations. You record or run a spectrum and analyze a sample by spectroscopy. The instrument is a spectrometer or spectrophotometer; the plural of 'spectrum' is 'spectra'.
Examples
We confirmed the structure using IR and NMR spectroscopy.
UV-Vis spectroscopy is a quick way to measure the concentration of colored solutions.
Usage note
Spectroscopy studies how light interacts with matter. Mass spectrometry measures the masses of ions and does not use light, although people often group the two together.
Common phrases
IR spectroscopy · UV-Vis spectroscopy · NMR spectroscopy · record a spectrum
A solution whose concentration is known accurately. It is used to find the concentration of other solutions in titrations or to build calibration curves.
Where you use it
Used in quantitative analysis. You prepare a standard solution by weighing a primary standard, or you standardize a solution against one. For calibration you make a series of standards at different concentrations.
Examples
Prepare a standard solution of potassium hydrogen phthalate to standardize the NaOH.
We made five standard solutions between 1 and 10 ppm for the calibration.
Common phrases
prepare a standard solution · primary standard · standardize a solution · working standard
The point in a titration where the indicator changes color or the signal changes sharply, showing that the reaction is complete and you should stop adding titrant.
Where you use it
Used in titration practice and reports. You approach, reach, detect or overshoot the endpoint. Strictly, the equivalence point is where the amounts react exactly; a good indicator puts the endpoint very close to it.
Examples
Add the titrant drop by drop as you approach the endpoint.
I overshot the endpoint, so the solution is dark pink instead of pale pink.
Usage note
Also written 'end point'. People often use endpoint (what you observe) and equivalence point (the theoretical point) loosely as synonyms, but keep them apart in reports.
Common phrases
reach the endpoint · overshoot the endpoint · endpoint detection · sharp endpoint · equivalence point
A group of methods that separate the parts of a mixture as they travel at different speeds through a stationary phase, carried by a moving liquid or gas called the mobile phase.
Where you use it
Used daily for analysis and purification. Common types are TLC (thin-layer), column chromatography, GC (gas) and HPLC (high-performance liquid chromatography). You run, load or elute a column and read retention times or Rf values.
Examples
We separated the two products by column chromatography on silica gel.
Gas chromatography showed that the sample was 98% pure.
Common phrases
column chromatography · thin-layer chromatography · gas chromatography · run a column · mobile phase
An analysis method that turns molecules into ions, separates the ions by their mass-to-charge ratio (m/z) and uses the result to find molecular mass and structure.
Where you use it
Used for identification, purity checks and trace analysis, often coupled with chromatography as GC-MS or LC-MS. You run a sample on the mass spectrometer and look for the molecular ion peak. Short forms: MS or, in speech, 'mass spec'.
Examples
Mass spectrometry showed a molecular ion at m/z 46, which fits ethanol.
Send the sample for mass spectrometry to confirm the molecular weight.
Common phrases
GC-MS · LC-MS · mass spectrum · molecular ion peak · high-resolution mass spectrometry
Short for nuclear magnetic resonance: a method that places a sample in a strong magnetic field and uses radio waves to show how the hydrogen or carbon atoms in a molecule are arranged.
Where you use it
The main structure-checking tool in organic labs. You run or take an NMR, a proton (¹H) or carbon (¹³C) NMR, dissolve the sample in a deuterated solvent such as CDCl₃, and discuss peaks, chemical shifts and integration.
Examples
The proton NMR shows a three-proton singlet at 2.1 ppm, typical of a methyl ketone.
Can you run an NMR of the crude product before we purify it?
Common phrases
proton NMR · carbon-13 NMR · run an NMR · NMR spectrum · NMR tube
A graph of instrument signal against the known concentrations of several standards. The concentration of an unknown sample is read from it using the sample's signal.
Where you use it
Used in UV-Vis, AAS, HPLC and many other quantitative methods. You prepare standards, plot the calibration curve, check its linearity (R²) and make sure your samples fall within its range. It is also called a standard curve.
Examples
The calibration curve was linear from 1 to 20 mg/L, with an R² of 0.999.
This sample is above the top standard, so dilute it and read it again against the calibration curve.
Common phrases
plot a calibration curve · linear calibration curve · standard curve · calibration range
Ten questions from this glossary. Pick the right meaning for each term and see your score.
How to learn chemistry vocabulary
Read real texts from the field: lab manuals, the experimental sections of research papers, safety data sheets and instrument guides show how chemists actually use these words.
Learn verbs together with their nouns, the way procedures are written: 'dissolve the solid', 'filter off the precipitate', 'make up to the mark', 'heat under reflux'.
Practice reading formulas, equations and numbers aloud: 'H two O', 'two H two plus O two gives two H two O', 'zero point one molar'. English uses a decimal point, not a comma.
Learn the English names of common elements and ions early, because many differ from Turkish: iron, copper, lead, tin, nitrogen, sulfur, chloride, sulfate.
After each experiment, write a few lines of lab notes in English: what you did, what you observed and what you think it means.
Frequently asked questions
How can I learn English for chemistry?
Read real texts from the field and notice how the words are used: textbook chapters, lab manuals, the experimental sections of papers and safety data sheets. Learn terms with their usual partners (prepare a solution, filter off a precipitate, adjust the pH) and use them straight away in your own lab notes and reports.
Which chemistry terms should I learn first?
Start with the words you meet in every lecture and every lab session: atom, element, compound, molecule, mole, solution, concentration, acid, base, pH, reaction, catalyst, beaker, pipette, fume hood and safety data sheet. Then move on to bonding, stoichiometry, organic chemistry and analytical methods. This glossary follows the same order, from the most essential terms to more specialist ones.
How do you read chemical formulas and equations aloud in English?
Say the symbols as letters and the numbers as numbers: H₂O is 'H two O', CO₂ is 'C O two' and H₂SO₄ is 'H two S O four'. For common substances chemists usually say the name instead: water, carbon dioxide, sulfuric acid. Read the arrow as 'gives', 'forms' or 'reacts to form', the plus sign as 'plus' or 'and', and a charge such as Fe³⁺ as 'F E three plus' or 'iron three ion'.
Why are some element names so different in English and Turkish?
Turkish took many element names from French, so they look close to English: sodyum and sodium, potasyum and potassium, kalsiyum and calcium. Metals known since ancient times, however, have old English names: iron (demir), copper (bakır), silver (gümüş), gold (altın), lead (kurşun) and tin (kalay). Their symbols come from Latin, which is why iron is Fe and lead is Pb. Turkish 'azot' is 'nitrogen' and 'kükürt' is 'sulfur' (UK: sulphur) in English.
