A-LEVEL OCR CHEMISTRY A PAPER 2: SYNTHESIS AND ANALYTICAL TECHNIQUES | JUNE 2025 EXAM | LA, Exams of Nursing

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A-LEVEL OCR CHEMISTRY A PAPER 2:

SYNTHESIS AND ANALYTICAL

TECHNIQUES | JUNE 2025 EXAM | LATEST

2024 – 2025 QUESTION PAPER WITH MARK

SCHEME AND DETAILED ANSWERS\

ALREADY GRADED A+

Empirical Formula - --ANSWER IS -- - The formula that shows the simplest whole-number ratio of atoms of each element present in a compound Enantiomers - --ANSWER IS -- - Stereoisomers that are nonsuperimposable mirror images of each other; also called optical isomers End Point - --ANSWER IS -- - The point in a titration at which an indicator changes colour; the end point indicates when the reaction is just complete Endothermic reaction - --ANSWER IS -- - A reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat being taken in from the surroundings (∆H is positive). Enthalpy H - --ANSWER IS -- - The heat content that is stored in a chemical system Enthalpy change ΔH - --ANSWER IS -- - The difference between the enthalpy of the products and the enthalpy of the reactants Enthalpy Cycle - --ANSWER IS -- - A diagram showing alternative routes between reactants and products which allows the indirect

determination of an enthalpy change from other known enthalpy changes using Hess' law. Enthalpy Profile Diagram - --ANSWER IS -- - A diagram for a reaction to compare the enthalpy of the reactants with the enthalpy of the products. Entropy - --ANSWER IS -- - The measurement used for the dispersal of energy and disorder within the chemicals making up the chemical system Equilibrium Constant Kc - --ANSWER IS -- - A measure of the position of equilibrium; the magnitude of an equilibrium constant indicates whether there are more reactants or more products in an equilibrium system. Equivalence Point - --ANSWER IS -- - The point in a titration at which the volume of one solution has reacted exactly with the volume of the second solution Esterification - --ANSWER IS -- - A reaction in which a carboxylic acid reacts with an alcohol to form an ester and water.

Fragmentation - --ANSWER IS -- - The process in mass spectrometry that causes a positive ion to split into pieces, one of which is a positive fragment ion. Free Energy Change ΔG - --ANSWER IS -- - The balance between enthalpy, entropy and temperature for a process given by ΔG = ΔH − TΔS. A process is feasible when ΔG < 0. Functional Group - --ANSWER IS -- - The part of the organic molecule responsible for its chemical reactions. General Formula - --ANSWER IS -- - The simplest algebraic formula of a member of a homologous series. For example, the general formula of the alkanes is CnH2n+ Giant Covalent Lattice - --ANSWER IS -- - A three-dimensional structure of atoms, bonded together by strong covalent bonds. Giant Ionic Lattice - --ANSWER IS -- - A three-dimensional structure of oppositely charged ions, bonded together by strong ionic bonds. Giant Metallic Lattice - --ANSWER IS -- - A three-dimensional structure of positive ions and delocalised electrons, bonded together by strong metallic bonds.

Group - --ANSWER IS -- - A vertical column in the periodic table. Elements in a group have similar chemical properties and their atoms have the same number of outer shell electrons Half-Life - --ANSWER IS -- - The time taken for the concentration of a reactant to decrease by half Hess's Law - --ANSWER IS -- - If a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route. Heterogenous Catalysis - --ANSWER IS -- - A reaction in which the catalyst has a different physical state from the reactants; frequently reactants are gases whilst the catalyst is a solid. Hetergenous Equilibrium - --ANSWER IS -- - An equilibrium in which the species making up the reactants and products have different physical states. Heterolytic Fission - --ANSWER IS -- - The breaking of a covalent bond with both of the bonded electrons going to one of the atoms, forming a cation and an anion

one molecule and a lone pair of electrons on a highly electronegative atom containing N, O or F on a different molecule. Hydrolysis - --ANSWER IS -- - A reaction with water that breaks a chemical compound into two compounds, the H and OH in a water molecule becomes incorporated into the two compounds. Induced Dipole-Dipole Interaction - --ANSWER IS -- - Attractive forces between induced dipoles in different molecules- also called London Forces Infrared Spectroscopy - --ANSWER IS -- - An instrumentation method of analysis that identifies bonds from absorption of the infrared radiation of different wavelengths Initial Rate of Reaction - --ANSWER IS -- - The change in concentration of a reactant or product per unit time at the start of the reaction when t= Initiation - --ANSWER IS -- - The first stage in a radical reaction in which radicals are generated when a covalent bond is broken by homolytic fission Intermediate - --ANSWER IS -- - A species formed during a reaction that reacts further and is not present in the final products

Intermolecular force - --ANSWER IS -- - An attractive force between molecules. Intermolecular forces can be London forces, permanent dipole-dipole interactions or hydrogen bonding. Ion - --ANSWER IS -- - A positively or negatively charged atom or a (covalently bonded) group of atoms (a polyatomic ion), where the number of electrons is different from the number of protons Ionic Bonding - --ANSWER IS -- - The electrostatic attraction between oppositely charged ions Ionic Product of Water Kw - --ANSWER IS -- - The product of the ions formed in the partial dissociation of water, given by Kw = [H+ (aq)] [OH− (aq)]. Isotopes - --ANSWER IS -- - Atoms of the same element with different numbers of neutrons and different masses Lattice Enthalpy - --ANSWER IS -- - The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions

Molar Gas Volume Vm - --ANSWER IS -- - The volume per mole of gas molecules at a stated temperature and pressure Molar Mass M - --ANSWER IS -- - The mass per mole of a substance, in units of gmol^- 1 Mole - --ANSWER IS -- - The amount of any substance containing as many elementary particles as there are carbon atoms in exactly 12 g of the carbon-12 isotope, that is, 6.02 × 1023 particles. Molecular Formula - --ANSWER IS -- - A formula that shows the number and type of atoms of each element present in a molecule Molecular Ion - --ANSWER IS -- - The positive ion formed in mass spectrometry when a molecule loses an electron. Molecule - --ANSWER IS -- - The smallest part of a covalent compound that can exist while retaining its chemical identity, consisting of 2 or more atoms covalently bonded together Monomer - --ANSWER IS -- - A small molecule that combines with many other monomers to form a polymer.

Neutralisation - --ANSWER IS -- - A chemical reaction in which an acid and a base react together to produce a salt and water Nomenclature - --ANSWER IS -- - A system of naming compounds Non-Polar - --ANSWER IS -- - No charge separation across a bond or in a molecule Nucleophile - --ANSWER IS -- - An atom (or group of atoms) that is attracted to an electron- deficient centre or atom, where it donates a pair of electrons to form a new covalent bond. Nucleophilic Substitution - --ANSWER IS -- - A reaction in which a nucleophile is attracted to an electron-deficient carbon atom, and replaces an atom or group of atoms on the carbon atom Optical Isomers - --ANSWER IS -- - Stereoisomers that are non- superimposable mirror images of each other; also called 'enantiomers' Order - --ANSWER IS -- - The power to which the concentration of a reactant is raised in the rate equation

Pauling Electronegativity Value - --ANSWER IS -- - A value assigned as a measure of the relative attraction of a bonded atom for the pair of electrons in a covalent bond Percentage Yield - --ANSWER IS -- - % yield = ((actual amount, in mol, of product)/( theoretical amount, in mol, of product)) × 100. Period - --ANSWER IS -- - A horizontal row of elements in the periodic table. Elements show trend in properties across a period Periodicity - --ANSWER IS -- - A repeating trend in properties of the elements across each period of the periodic table Permanent Dipole - --ANSWER IS -- - A small charge difference that does not change across a bond, with δ+ and δ− partial changes on the bonded atoms: the result of the bonded atoms having different electrongativities. Permanent Dipole-Dipole Interaction - --ANSWER IS -- - An attractive force between permanent dipoles in neighbouring polar molecules. pH - --ANSWER IS -- - pH = −log[H+ (aq)]

Polar molecule - --ANSWER IS -- - δ+ and δ− charges at different ends of the molecule. Has an overall dipole, having taken into account any dipoles across bonds and the shape of the molecule Polar Covalent Bond - --ANSWER IS -- - A bond with a permanent dipole, having δ+ and δ− partial changes on the bonded atoms Polyatomic Ion - --ANSWER IS -- - An ion composed of more than one atom Polymer - --ANSWER IS -- - A large molecule formed from many thousands of repeat units of smaller molecules known as monomers Position of Equilibrium - --ANSWER IS -- - The relative quantities of reactants and products, indicating the extent of a reversible reaction at equilibrium Precipitation Reaction - --ANSWER IS -- - The formation of a solid from a solution during a chemical reaction. Precipitates are often formed when two aqueous solutions are mixed together. Primary - --ANSWER IS -- - On a carbon atom at the end of a chain

Rate of Reaction - --ANSWER IS -- - the change in concentration of a reactant or product in a given time Rate-Determining Step - --ANSWER IS -- - The slowest step in the reaction mechanism of a multi-step reaction Reaction Mechanism - --ANSWER IS -- - The sequence of bond breaking and bond-forming steps that shows the path taken by electrons during a reaction. Redox Reaction - --ANSWER IS -- - A reaction involving reduction and oxidation Reducing Agent - --ANSWER IS -- - A reagent that reduces (adds electrons to) another species Reduction - --ANSWER IS -- - Gain of electrons or a decrease in oxidation number Reflux - --ANSWER IS -- - The continual boiling and condensing of a reaction mixture back to the original container to ensure that the reaction takes place without the contents of the flask boiling dry.

Relative Atomic Mass Ar - --ANSWER IS -- - The weighted mean mass of an atom of an element compared with 1/12 of the mass of an atom of carbon- 12 Relative Formula Mass - --ANSWER IS -- - The weighted mean mass of the formula unit of a compound compared with 1/12 of the mass of an atom of carbon-12. Relative Isotopic Mass - --ANSWER IS -- - The mass of an atom of an isotope compared with 1/12 of the mass of an atom of carbon- 12 Relative Molecular Mass Mr - --ANSWER IS -- - The weighted mean mass of a molecule of a compound compared with 1/12 of the mass of an atom of carbon- 12 Repeat Unit - --ANSWER IS -- - A specific arrangement of atoms that occurs in the structure over and over again. Repeat units are included in brackets, outside of which is the symbol n. Retention Time - --ANSWER IS -- - In gas chromatography. The time for a component to pass from the column inlet to the detector Reversible Reaction - --ANSWER IS -- - A reaction that takes place in both forward and reverse directions