Definitions YR13 Flashcards
What is NMR spectroscopy?
An analytical technique that allows the structure of a molecule to be determined by analysing bond and atom environments.
What is an environment (NMR)?
The environment of an atom depends on the surrounding atoms and bonds in the molecule.
What are stereoisomers?
Molecules that have the same structural formula but a different arrangement of atoms in space (E-Z/optical)
What are optical isomers?
Non-superimposable mirror images which rotate the plane of plane-polarised light in an equal amount but opposite directions.
What is plane-polarised light?
Light which oscillates in one plane.
What is a polarimeter?
Apparatus which can be used to measure the rotation of plane-polarised light.
What is a chiral carbon?
A chiral carbon has four different groups bonded to it (chiral centre/asymmetric carbon).
What are enantiomers?
Optical isomers of the same molecule
What is a racemic mixture?
A racemic mixture (racemate) is a 50-50 mixture of the two enantiomers of an optical isomer, so doesn’t rotate the plane of plane-polarised light as the rotations cancel.
What are carbonyl compounds?
Aldehydes or ketones (at A Level). The carbonyl group is C=O.
What are hydrolysis reactions?
Reactions in which a compound is split apart in a reaction involving water.
What are condensation reactions?
Reactions which join two molecules together via the removal of a small molecule (usually water).
What are condensation polymers?
Condensation polymers are produced when monomers join together via condensation reactions. This produces the polymer and a small molecule.
What is a dynamic equilibrium?
Where the rates of forwards and backwards reactions are equal, so the relative quantities of reactants and products are unchanging.
What is a closed system?
One in which the reactants and products (or anything else) cannot enter of leave
What is Le Chatilier’s principle?
This states that if a constraint (new condition) is imposed upon a system, the system will act to counteract that constraint.
What is the equilibrium constant?
Symbol Kc or Kp, it is a ratio between the reactants and products at equilibrium. It is constant unless the temperature of the equilibrium system is changed.
What is a homogenous system?
One in which all reactants and products are in the same states.
What is a heterogenous system?
One in which not all reactants and products are in the same state.
What is the partial pressure of a gas?
The pressure it would exert if it alone filled its container. Calculated via mole fraction of gas x total pressure.
What is a Brønsted-Lowry acid?
A proton donor.
What is a Brønsted-Lowry base?
A proton acceptor.
What is a conjugate acid?
Formed when a base accepts a proton.
What is a conjugate base?
Formed when an acid donates a proton.
What is a conjugate acid-base pair?
A pair of species on opposite sides of an equation which are related, and differ only by their number of protons.
What is monoprotic (monobasic) acid?
Can donate one proton per molecule (e.g. HCl).
What is a diprotic (dibasic) acid?
Can donate two protons per molecule (e.g. H2SO4).
What is a triprotic (tribasic) acid?
Can donate three protons per molecule (e.g. H3PO4).
What is pH?
-log[H+]
What are strong acids?
Acids which fully ionise (dissociate) to produce H+ ions when in solution in water.
What are weak acids?
Acids which partially ionise (dissociate) to produce H+ ions when in solution in water
What is the ionic product of water?
Kw = [H+][OH-]
What is the acid dissociation constant?
Ka = [H+][A-]/[HA]
What is pKa?
-log(Ka)
What is the enthalpy change of neutralisation?
The enthalpy change when one mole of water is formed by neutralisation between an acid and a base under standard condition (298K).
What is the equivalence point?
The point during a titration at which the reactants have fully reacted (for acid/base, mol H+=mol OH-)
What is the half-equivalence point?
The point during a titration where exactly half the reactant in the conical flask has been reacted.
What is a pH curve?
A graph drawn of pH (y axis) against volume of acid or alkali added (x axis).
What is the buffer region of a pH curve?
The region where pH only changes slightly as acid/alkali is added.
What are indicators?
Weak acids where the protonated species and the deprotonated salt species have different colours.
What is a buffer solution?
A mixture of a weak acid and its salty that will resist changes in pH when small amounts of acid or alkali are added.
What is the enthalpy of atomisation?
The enthalpy change when one mole of gaseous atoms are produces from an element in its standard state under standard conditions.
What is the standard enthalpy of solution?
The enthalpy change when one mole of a solute dissolves completely in a solvent to form a solution in which the ions are far enough apart not to interact with each other, under standard conditions.
What is the enthalpy of hydration?
The enthalpy change when water molecules surround one mole of gaseous ions, under standard conditions.
What is the first electron affinity?
The enthalpy change when one mole of electrons is added to a mole of gaseous atoms to form ions with a 1- charge.
What is the second electron affinity?
The enthalpy change when a mole of electrons is added to a mole of gaseous 1- ions to form ions with a 2- charge.
What is the enthalpy of lattice formation?
The enthalpy change when one mole of a solid ionic compound is formed from its gaseous ions.
What is the enthalpy of lattice dissociation?
The enthalpy change when one mole of a solid ionic compound is dissociated into its gaseous ions.
What is entropy (S)?
A measure of disorder
What is the entropy of a system (Ssystem)?
The entropy within a chemical reaction (system).
What is the entropy of surroundings (Ssurroundings)?
The entropy of the surroundings of a chemical reaction (system).
What is the Gibbs free energy?
The change is Gibbs energy (deltaG) is used to determine if a reaction is feasible.
What is a half-cell/electrode?
An equilibrium system consisting of a solid metal in a solution of its own ions.
What is the electrode potential (E)?
A measure of the equilibrium position for a half-cell/electrode.
What is the standard electrode potential?
The voltage produced by a half-cell when connected to a standard hydrogen electrode., under standard conditions (298K, 100KPa, all solutions 1 mol dm-3)
What is the standard hydrogen electrode?
Defined as having an electrode potential of 0.00V - consistst of a platinum electrode over which H2 gas is passed at 100KPa pressure in a solution of 1 mol dam-3 H+ ions, all at 298K.
What is an electrochemical cell?
Produces a potential difference or electromotive force from a redox reaction. It is constructed from two half-cells with different electrode potentials joined together.
What is the electromotive force (emf or Ecell)?
A measure of the voltage of an electrochemical cell.
What is a salt bridge?
An ionic connection between the solutions of two half-cells
What is a storage cell?
A rechargeable cell.
What is a fuel cell?
A cell which uses a constant supply of fuel and oxidising agent to produce a voltage via a chemical reaction (without burning the fuel).
What is the anode?
The electrode where oxidation occurs?
What is the cathode?
The electrode where reduction occurs.
What is a redox titration?
A titration in which the concentration of a reducing or oxidising agent is determined via a redox reaction.
What does it mean to be amphoteric?
A substance is unable to act as an acid or as a base.
What is a zwitterion?
A molecule containing a positive charge on one group and a negative charge on another.
What is the isoelectric point of an amino acid?
The point at which the amino acid exists as a zwitterion in aqueous solution.
What is a d-block element?
An element which has its highest energy electron is a d-subshell
What is a transition metal?
A metal which forms at least one stable ion with partially filled d orbitals
What is a complex ion?
Consists of a central transition metal ion surrounded by ions or other molecules (ligands) that form co-ordinate (dative) bonds with it.
What is a ligand?
A species (ion or molecule) with a lone pair which is able to form co-ordinate bonds with transition metal ions.
What is the co-ordination number of a transition metal ion in a complex ion?
The number of coordinate bonds accepted by the transition metal ion.
What is a monodentate ligand?
A species that is only able to form one co-ordinate bond to a transition metal ion.
What is a bidentate ligand?
A species which can form two coordinate bonds to a transition metal ion.
What is a multidentate ligand?
A species which can form multiple (2 or more) coordinate binds to a transition metal ion.
What is the denticity of a ligand?
How many coordinate bonds it can form with a transition metal ion.
What is the chelate effect?
This occurs when multiple ligands of low denticity exchange for a lower number of ligands of higher denticity.
What is a catalyst?
It speeds up the rate of reaction by providing an alternative mechanism for a reaction with a lower activation energy (not used up).
What are heterogenous catalysts?
Catalysts which are in a different phase to the reactants.
What are homogenous catalysts?
Catalysts which are in the same phase as the reactants.
What is adsorption?
This is when a substance binds to the surface of another.
What is desorption?
When an adsorbed substance is released from a surface.
What is catalyst poisoning?
When some substances (impurities in the reaction mixture), permanently adsorb to the surface of the catalyst, reducing the surface area and number of available active sites on the catalysts.
What is autocatalysis?
This occurs when a reaction is catalysed by one of its own products.
What are aryl (aromatic) compounds?
Compounds which contain at least one benzene ring
What are alkyl (aliphatic) compounds?
Compounds which do not contain a benzene ring
What are delocalised electrons?
Bonding electrons which are not fixed between two atoms in a bond, but shared between three or more atoms.
What is resonance?
A way of describing the delocalisation of electrons
What is reflux?
A technique where a mixture is continuously boiled and condensed, usually via the use of a reflux condenser (vertical).
What is distillation?
A technique used to separate compounds with different boiling points.
What is fractional distillation?
Uses a fractionating column to ensure separation of compounds with similar boiling points.
What are anti bumping granules?
Used to ensure smooth boiling, by providing a nucleation site for bubbles to form during boiling.
What is solvent extraction?
This involves using a solvent to extract a desired compound from a mixture. The extraction solvent must be immiscible with the original solvent, and the desired compound must be more soluble in the extraction solvent than the original solvent (uses a separating funnel).
What are drying agents?
Used to absorb water from organic liquids (e.g. anhydrous MgSO4)
What is recrystallisation?
The process of purifying an organic liquid by dissolving it in the minimum volume of hot solvent needed to produce a saturated solution and then cooling it to cause crystals to form.
