In Augment’s notes, a marked term shows its definition when you hover or tap it, and each page ends with the terms it introduces.
131 terms from What are the mechanisms of chemical change?, each defined in a sentence or two, with the part of the syllabus where you first meet it. 55 of them are HL only, and marked.
A weak acid, HInd, whose un-ionized form and conjugate base have different colours; it changes colour over a pH range of roughly .
A buffer made of a weak acid and a salt of its conjugate base, such as ethanoic acid with sodium ethanoate; its pH is below 7.
An electrode that takes part in the electrode reaction, such as a copper anode that is oxidized and dissolves during electrolysis.
A reaction in which two reactants combine to form a single product, as when a molecule adds across the double bond of an alkene.
A single species formed when a Lewis acid and a Lewis base combine through a coordination bond without any atoms being lost, such as from and .
A base that dissolves in water to form hydroxide ions, , such as sodium hydroxide or aqueous ammonia. Every alkali is a base, but insoluble bases such as are not alkalis.
Able to act as both a Brønsted–Lowry acid and a Brønsted–Lowry base, by donating or accepting a proton; examples are , and .
The insoluble residue of less reactive metals, such as silver, gold and platinum, that collects beneath the anode during electrolytic refining.
A base taken to neutralize excess hydrochloric acid in the stomach, such as calcium carbonate, magnesium hydroxide or sodium hydrogencarbonate.
The reaction in which water molecules transfer protons to each other, ; it occurs to a very small extent and is endothermic.
Approach of a nucleophile to a carbon atom from the side directly opposite the leaving group, as in the mechanism.
The equilibrium constant for the reaction of a weak base with water, ; the larger its value, the stronger the base.
A buffer made of a weak base and a salt of its conjugate acid, such as ammonia with ammonium chloride; its pH is above 7.
A concentrated aqueous solution of sodium chloride, electrolysed in industry to make chlorine, hydrogen and sodium hydroxide.
An orange solution of bromine in water used to test for C=C double bonds: an alkene decolourizes it rapidly, even in the dark, while an alkane does not.
A species that donates a proton, , to another species in a reaction.
A species that accepts a proton, , from another species; it needs a lone pair of electrons to bond to the proton.
The amount of acid or alkali a buffer can absorb before its pH changes significantly; it is larger for more concentrated buffers and falls when a buffer is diluted.
The flat part of a pH curve, before equivalence for a weak acid titrated with a strong base, where both the weak acid and its conjugate base are present and the pH changes only slowly.
A solution that resists a change in pH when small amounts of acid or alkali are added; it contains a weak acid and its conjugate base, or a weak base and its conjugate acid.
An ion with a negative charge on a carbon atom, which carries a lone pair, such as .
An ion with a positive charge on a carbon atom that has only three bonds, such as . It is planar round the positive carbon; stability increases from primary to secondary to tertiary.
A reaction in which a reactive intermediate, such as a radical, is regenerated in each cycle of steps, so one initiation event leads to many product molecules.
The industrial electrolysis of brine, producing chlorine at the anode and hydrogen and sodium hydroxide at the cathode.
A compound of carbon, chlorine and fluorine, such as , once used as a refrigerant and aerosol propellant; in the stratosphere UV light releases chlorine atoms from it that destroy ozone.
A reaction in which bond breaking and bond making happen at the same time in a single step, with no intermediate, as in the mechanism.
The species formed when a base has gained one proton: the conjugate acid of is .
Two species that differ by a single proton, , such as and , or and .
The species left when an acid has lost one proton: the conjugate base of is .
The gradual oxidation of a metal at its surface by substances in its surroundings, such as oxygen and water.
A curved arrow with a full arrowhead, used in mechanisms to show the movement of a pair of electrons, from a lone pair or bond to the atom or bond where the pair ends up.
A voltaic cell made of a zinc electrode in zinc sulfate solution and a copper electrode in copper(II) sulfate solution, joined by a salt bridge; zinc is the anode.
The number of multiple bonds and rings in a molecule; each mole of added in hydrogenation removes one degree of unsaturation.
A redox reaction in which atoms of the same element in one species are both oxidized and reduced, as in , where chlorine goes from 0 to −1 and to +1.
The bubbling seen when a gas is produced in a liquid, for example when a reactive metal reacts with a dilute acid.
An arrangement in which oxidation and reduction take place at two separate electrodes joined by an external circuit; voltaic and electrolytic cells are the two types.
A list of redox couples in order of their standard electrode potentials; oxidizing agents become stronger towards the positive end and reducing agents towards the negative end.
A conductor, usually a metal or graphite, through which electrons enter or leave the electrolyte in an electrochemical cell; oxidation or reduction takes place at its surface.
An electrochemical cell in which an external dc supply drives a non-spontaneous redox reaction, converting electrical energy into chemical energy; its anode is positive and its cathode negative.
Purifying a metal by electrolysis with the impure metal as the anode and a thin sheet of pure metal as the cathode, in a solution of the metal's ions.
A reactant that forms a bond to its reaction partner (the nucleophile) by accepting both bonding electrons from it; it is electron-deficient and may be positive, such as and , or neutral, such as and .
An addition reaction in which an electrophile attacks the electron-rich C=C double bond of an alkene and the two parts of the reagent add to the two carbon atoms, giving a saturated product.
Using electrolysis to coat an object with a thin layer of metal; the object is the cathode, the plating metal the anode, and the electrolyte contains ions of the plating metal.
The wire and any meter or device that connect the two electrodes of a cell; electrons flow through it from the anode to the cathode.
The charge carried by one mole of electrons, ; it is the Avogadro constant multiplied by the charge of one electron.
A curved arrow with half an arrowhead, used in mechanisms to show the movement of one electron, as in homolytic fission.
A substitution reaction that proceeds by a radical chain mechanism (initiation, propagation, termination), such as the reaction of an alkane with chlorine or bromine in UV light.
Coating iron or steel with a layer of zinc. The zinc is oxidized in preference to the iron, so it protects the iron even where the coating is scratched.
One half of a voltaic cell: an electrode in contact with an electrolyte, such as a metal dipping into a solution of its own ions, where either oxidation or reduction occurs.
The point in a titration at which half the volume needed for equivalence has been added. For a weak acid, there, so .
A Lewis acid catalyst such as or that accepts an electron pair from a halogen molecule, polarizing it so that it can substitute into a benzene ring.
A reaction that introduces one or more halogen atoms into a molecule, for example the chlorination of methane to chloromethane.
The logarithmic form of the expression used for buffers: .
The breaking of a covalent bond in which both bonding electrons stay with one fragment, forming a cation and an anion, for example .
A voltmeter that lets almost no current flow, so that no reaction occurs in the cell and the maximum potential difference between its electrodes is measured.
An apparatus with two graduated tubes joined to a central reservoir, used to electrolyse water and collect and measure the hydrogen and oxygen formed.
The addition of water across a C=C double bond to form an alcohol, as in with an acid catalyst.
A compound of carbon, hydrogen and fluorine, such as , used in place of CFCs; it contains no chlorine so does not destroy ozone, but many are strong greenhouse gases.
The addition of hydrogen across a carbon–carbon double or triple bond, using a metal catalyst such as nickel; it is a reduction that lowers the degree of unsaturation.
A reaction in which a bond is broken by reaction with water (or hydroxide ions), as when a halogenoalkane is converted into an alcohol.
The shift of electron density along σ bonds towards a more electronegative atom or away from an electron-releasing group such as an alkyl group. Electron-withdrawing chlorine atoms make chloroethanoic acids stronger than ethanoic acid.
An electrode, usually graphite or platinum, that conducts electricity but does not itself take part in the reaction at its surface.
The first step of a radical chain reaction, in which radicals are formed from a molecule with none, usually by homolytic fission in UV light or heat: .
A property that does not depend on the amount of substance, such as temperature, density or electrode potential.
The turning inside out of the arrangement of groups round a carbon atom during an reaction, so that the product has the opposite three-dimensional arrangement to the reactant.
, equal to at 298 K; it applies to every aqueous solution and increases with temperature.
A secondary cell with a lead negative electrode and a lead(IV) oxide positive electrode in sulfuric acid; both electrodes form lead(II) sulfate on discharge, and each cell gives about 2 V.
The atom or group that leaves a substrate in a substitution reaction, taking the bonding pair with it, such as a halide ion from a halogenoalkane.
An electron-pair acceptor. Examples include , , and transition element ions such as ; many Lewis acids have no proton to donate.
An electron-pair donor: a species with a lone pair that it shares to form a coordination bond, such as , , or . Every Brønsted–Lowry base is also a Lewis base.
A reaction in which the ligands of a complex ion are replaced by other ligands, such as .
A secondary cell in which lithium ions move through an organic electrolyte between a graphite electrode and a metal oxide electrode such as ; it gives about 3.7 V.
The product formed in the greater amount when a reaction can give more than one product; the other is the minor product. In additions to unsymmetrical alkenes it forms through the more stable carbocation.
When HX or water adds to an unsymmetrical alkene, the hydrogen atom adds to the double-bond carbon that already has more hydrogen atoms. It is explained by the greater stability of the more substituted carbocation.
An electrolytic cell for the chlor-alkali process in which a membrane that lets only cations through separates the anode and cathode compartments, so chlorine and sodium hydroxide are kept apart.
An acid that can donate one proton per molecule, such as , or ; sulfuric acid, which can donate two, is diprotic.
The international agreement of 1987 that phased out the production of CFCs and other ozone-depleting substances.
The reaction of an acid with a base to form a salt and, usually, water; for strong acids and bases in water the ionic equation is .
A mixture of concentrated nitric acid and concentrated sulfuric acid, which generates the nitronium ion and is used to nitrate benzene below about 50 °C.
The linear cation (O=N⁺=O), the electrophile in the nitration of benzene, formed from concentrated nitric and sulfuric acids.
A reactant that forms a bond to its reaction partner (the electrophile) by donating both bonding electrons; it has a lone pair and may be neutral, such as and , or negative, such as .
A reaction in which a nucleophile donates an electron pair to form a new bond to an atom (usually a δ+ carbon) while another bond to that atom breaks and releases a leaving group, as in .
The extra voltage, beyond the value predicted from electrode potentials, needed to make an electrode reaction take place at a useful rate; it is large for the formation of oxygen.
The ion , formed when a water molecule accepts a proton; it is how a hydrogen ion exists in aqueous solution, so and are used interchangeably.
The region of the stratosphere, mostly 15–35 km up, where ozone absorbs most of the Sun's harmful ultraviolet radiation; its thinning by chlorine atoms from CFCs is called ozone depletion.
The acid (or base) from which a salt can be made by neutralization: sodium ethanoate has the parent acid and the parent base .
Reaction of a weak acid with less than the equivalent amount of strong base (or of a weak base with too little strong acid), leaving a mixture of the weak species and its conjugate: a buffer.
The percentage of the molecules of a weak acid or base that are ionized at equilibrium, for an acid . It increases as the solution is diluted.
A logarithmic measure of acidity: , so . A fall of one pH unit is a tenfold increase in .
A graph of the pH of the solution in a titration against the volume of titrant added; its steep section marks the equivalence point.
An instrument whose glass-membrane probe measures pH precisely, usually to two decimal places; it is calibrated with buffer solutions of known pH before use.
. The smaller the pKa, the stronger the acid; one unit corresponds to a tenfold change in .
. The smaller the pKb, the stronger the base. For a conjugate pair at 298 K, .
A finely divided form of platinum coated onto a platinum electrode to give a large surface area, on which the equilibrium between hydrogen gas and hydrogen ions is reached quickly.
The negative logarithm to base 10 of the hydroxide ion concentration: . At 298 K, .
In electrolysis, the conversion of one ion or molecule rather than another into a neutral product at an electrode; it depends on electrode potentials, concentration and the electrode material.
A voltaic cell whose redox reaction cannot be reversed in practice, so it is used once and discarded; an alkaline zinc–manganese(IV) oxide cell is an example.
A halogenoalkane in which the carbon bonded to the halogen is bonded to one other carbon atom (or none), such as 1-bromobutane, .
A step in a chain reaction in which a radical reacts with a molecule to form a new molecule and a new radical, so the number of radicals does not change.
A species with an unpaired electron, shown with a dot, for example ; radicals are formed by homolytic fission and are usually very reactive.
The sequence of elementary steps by which reactants are converted into products. The steps must add up to the overall stoichiometric equation.
A list of metals in order of how easily they are oxidized to their positive ions; a metal higher in the series displaces a lower one from a solution of its ions.
The oxidized and reduced forms of one species that are converted into each other by gaining or losing electrons, such as or .
A reaction in which oxidation and reduction occur together: one species loses electrons (its oxidation state increases) and another gains them (its oxidation state decreases).
A half-cell of known, stable potential against which the potentials of other half-cells are measured; the standard hydrogen electrode is the primary reference.
Continuous boiling of a reaction mixture with a vertical condenser above it, so that vapours condense and return to the flask; it allows prolonged heating without loss of volatile substances.
The corrosion of iron or steel in the presence of both oxygen and water, forming hydrated iron(III) oxide, (rust).
Protecting iron from corrosion by connecting it to a more easily oxidized metal, such as zinc or magnesium, which is oxidized instead of the iron.
An ionic compound formed when the hydrogen of an acid is replaced by a metal ion or an ammonium ion, for example in neutralization.
A tube or strip of filter paper containing a solution of an unreactive salt, such as , that joins the two half-cells of a voltaic cell; its ions move to keep each solution electrically neutral and complete the circuit.
The reaction of an ion from a salt with water, in which a proton is transferred and or forms, so that the solution is acidic or basic; for example .
A voltaic cell whose redox reaction can be reversed by supplying electrical energy, so it can be recharged and reused; examples are the lead–acid and lithium-ion cells.
A halogenoalkane in which the carbon bonded to the halogen is bonded to two other carbon atoms, such as 2-bromobutane, .
A two-step nucleophilic substitution: the C–X bond breaks heterolytically in the slow step to give a carbocation, which then bonds to the nucleophile; rate . Typical of tertiary halogenoalkanes.
A one-step (concerted) nucleophilic substitution in which the nucleophile attacks the carbon from the side opposite the leaving group as the C–X bond breaks; rate . Typical of primary halogenoalkanes.
The potential difference between the electrodes of a voltaic cell under standard conditions with no current flowing: . It is positive for a spontaneous reaction.
The potential difference between a half-cell and the standard hydrogen electrode under standard conditions (298 K, 100 kPa, ), quoted for the reduction half-equation; symbol .
The reference half-cell, assigned a potential of exactly 0.00 V: hydrogen gas at 100 kPa bubbled over a platinized platinum electrode in a solution with at 298 K.
A reaction in which a particular stereoisomer of the reactant gives one particular stereoisomer of the product, such as the reaction, which inverts the configuration.
The slowing of a reaction because bulky groups get in the way of an approaching species, as when three methyl groups block backside attack on a tertiary halogenoalkane.
The layer of the atmosphere from about 10 to 50 km above the Earth's surface, which contains the ozone layer.
An acid that ionizes (dissociates) completely in aqueous solution, such as , , , and .
A base that is completely ionized in aqueous solution, such as the group 1 hydroxides.
A reaction in which one atom or group in a molecule is replaced by another atom or group, as when a chlorine atom replaces a hydrogen atom of methane.
The organic molecule that is attacked in a reaction, such as the halogenoalkane in a nucleophilic substitution.
A step in a chain reaction in which two radicals combine to form a molecule, removing radicals and ending a chain.
A halogenoalkane in which the carbon bonded to the halogen is bonded to three other carbon atoms, such as 2-bromo-2-methylpropane, .
A mixture of indicators that shows a range of colours across the pH scale, used to estimate pH to about the nearest whole unit.
An alkene whose two double-bonded carbon atoms carry different groups, such as propene, so that an adding molecule HX can give two different products.
An electrochemical cell that converts the chemical energy of a spontaneous redox reaction into electrical energy; its anode is negative and its cathode positive.
A base that is only partially protonated in aqueous solution, so its solution contains an equilibrium; examples are ammonia and amines.