OCR A-Level Chemistry
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Development of practical skills in chemistry
1.1 - Practical skills assessed in a written examination
1.1.1 - Planning practical investigationsGood practical chemistry starts before any chemicals are mixed. In this lesson you will learn how to turn a practical problem into a method that can answer the question, using suitable apparatus, controlled variables and chemical reasoning. The aim is not to memorise one perfect method for every...
1.1.2 - Implementing measurements and observationsGood practical chemistry is not just "doing the experiment". It means choosing apparatus that matches the measurement, using it safely and correctly, recording observations precisely, and presenting raw data so that another chemist can understand what was actually measured. This lesson builds the...
1.1.3 - Analysis, graphs and significant figuresThis lesson is about turning practical results into evidence. You will learn how to process qualitative and quantitative results, choose sensible significant figures, draw and interpret graphs, and use gradients, intercepts and tangents to support a valid conclusion.
1.1.4 - Evaluation, uncertainty and improvementsGood practical chemistry does not end when the readings have been recorded. You need to decide what the results show, how much confidence the evidence deserves, and how the method could be made stronger. This lesson teaches the language for evaluating data: anomalies, limitations, accuracy, preci...
1.2 - Practical skills assessed in the practical endorsement
1.2.1 - Practical endorsement skillsPractical chemistry is not only about getting a result. It is about planning a sensible method, using equipment safely, making reliable observations, keeping records that someone else can understand, processing data correctly, and acknowledging where information came from. These skills are assess...
1.2.2(a)-(c) - Core measurement, heating and pH techniquesThis lesson is about choosing apparatus because it fits the measurement, not because it is familiar. You will learn how to record mass, time, volumes and temperature, how to heat mixtures using water baths, electric heaters and sand baths, and how to measure pH with charts, meters and probes.
1.2.2(d)-(f) - Glassware, reflux, filtration and indicatorsThis lesson is about using common wet-chemistry apparatus accurately and safely. You are not learning a long list of practical recipes; you are learning why each piece of apparatus is chosen, what accuracy it gives, and what details make an experimental method valid.
1.2.2(g)-(l) - Purification, chromatography, cells, rates, safetyThis lesson is about choosing and using practical techniques accurately. You will learn how to handle solid and liquid products differently, how to check purity or separation using melting point and chromatography, how to set up an electrochemical cell for a voltage reading, and how to measure re...
Foundations in chemistry
2.1 - Atoms and reactions
2.1.1(a)-(b) - Atomic structure and isotopesAtoms are the counting units of chemistry, but exam questions often test them by asking for exact numbers of protons, neutrons and electrons. In this lesson you will learn how atomic number, mass number and ionic charge control those numbers, and why isotopes are still atoms of the same element.
2.1.1(c)-(e) - Relative mass and mass spectrometryAtoms are far too small to weigh one by one in grams, so chemists compare their masses on a relative scale. In this lesson you will learn the carbon-12 mass scale, how isotope data from mass spectrometry is used to calculate relative atomic mass, and when to use the terms relative molecular mass...
2.1.2 - Compounds, formulae and equationsChemical formulae and equations are the shorthand language used through the rest of chemistry. In this lesson you will learn how ionic charges determine formulae, how to balance equations without changing formulae, and how to write ionic equations that show only the particles that actually react.
2.1.3(a) - The mole and chemical amountChemists need a way to count particles that are far too small to count one by one. The amount of substance, measured in moles, is the counting quantity that connects particles, mass and gas volume. In this lesson you will learn the exact language and one-step conversions that later mole calculati...
2.1.3(b)-(d) - Empirical, molecular and hydrated formulaeA chemical formula is a ratio statement. In this lesson you will learn how composition data turns into an empirical formula, how relative molecular mass can scale that into a molecular formula, and how water of crystallisation is handled in hydrated salts. The common thread is simple but powerful...
2.1.3(e), 2.1.3(g) - Reacting masses, solutions and stoichiometryChemists use amount of substance, measured in mol, as the bridge between particles and measurable quantities. In this lesson you will use mass, gas volume, and solution concentration to find amounts in mol, then use balanced equations to link the amounts of different substances in a reaction. Thi...
2.1.3(f) - The ideal gas equationGases are often measured by their pressure, volume and temperature rather than by direct weighing. The ideal gas equation links those measurements to the amount of gas in moles, so it is a powerful route from experimental gas data to chemical amount. In this lesson, the main skill is choosing com...
2.1.3(h)-(j) - Percentage yield, atom economy and measurementA balanced equation can predict the maximum amount of product a reaction could make, but real experiments rarely give that perfect amount. This lesson teaches two different percentage calculations: percentage yield, which compares the actual product made with the theoretical maximum, and atom eco...
2.1.4(a)-(c) - Acids, bases, alkalis and neutralisationAcid-base chemistry starts with a simple particle idea: acids produce hydrogen ions in water, and alkalis produce hydroxide ions in water. In this lesson you will learn the common formulae, how to compare strong and weak acids qualitatively, and how to write balanced neutralisation equations for...
2.1.4(d)-(e) - Acid-base titrationsAcid-base titration is a practical method for finding an unknown concentration by reacting a measured volume with a solution whose concentration is known accurately. The chemistry is simple neutralisation, but the result is only trustworthy if the volumes, standard solution and mole-ratio calcula...
2.1.5(a)-(c) - Oxidation numbers and redox nomenclatureOxidation numbers are a bookkeeping system for tracking electrons in formulae, compounds and ions. In this lesson, the focus is not yet on full redox reactions. You will learn the rules for assigning oxidation numbers, how to use them to write formulae, and how Roman numerals make names such as i...
2.1.5(d)-(f) - Redox reactions and electron transferRedox reactions are reactions where electrons are transferred. In this lesson you will connect the electron-transfer definition to oxidation-number changes, write full equations for metals reacting with acids, and interpret unfamiliar redox equations by tracking what loses and gains electrons.
2.2 - Electrons, bonding and structure
2.2.1 - Electron structureElectrons are not arranged around a nucleus as neat circular tracks. In this lesson you will build the model used in A-level chemistry: shells contain sub-shells, sub-shells contain orbitals, and electron configurations record which orbitals are occupied. The aim is practical: by the end, you sho...
2.2.2(a)-(c) - Ionic bonding and giant ionic latticesIonic bonding explains how many metal and non-metal elements form compounds with high melting points, solid crystal structures and state-dependent electrical conductivity. In this lesson you will build the model from ion formation to dot-and-cross diagrams, then use the giant ionic lattice model...
2.2.2(d)-(f) - Covalent bonding and dot-and-cross diagramsCovalent bonding is the bonding model used for many molecules and molecular ions. In this lesson you will define a covalent bond precisely, construct dot-and-cross diagrams for single, multiple and coordinate bonds, and use average bond enthalpy as a qualitative measure of covalent bond strength....
2.2.2(g)-(h) - Shapes of simple molecules and ionsMolecules and ions are not flat lists of atoms. Their bonds point in three dimensions because electron pairs around a central atom repel each other and settle as far apart as possible. In this lesson you will use that electron-pair-repulsion model to predict the named OCR shapes, bond angles and...
2.2.2(i)-(j) - Electronegativity, bond polarity and dipolesElectronegativity explains why a covalent bond can have a slightly negative end and a slightly positive end. In this lesson, you will learn how to interpret Pauling electronegativity values, how a polar bond forms, and why molecular shape decides whether a molecule has an overall dipole.
2.2.2(k)-(l) - Intermolecular forces and hydrogen bondingMolecules can be covalently bonded inside themselves and still attract neighbouring molecules. This lesson builds the three intermolecular-force models you need here: induced dipole-dipole interactions, permanent dipole-dipole interactions and hydrogen bonding. The aim is to name each interaction...
2.2.2(m)-(o) - Water, simple molecular lattices and propertiesWater is a small covalent molecule, but its physical properties are not what a simple "small molecule" prediction would suggest. In this lesson you will use hydrogen bonding and simple molecular lattice models to explain why ice floats, why water has relatively high melting and boiling points, an...
Periodic table and energy
3.1 - The periodic table
3.1.1(a)-(c) - Periodic table, periodicity and ionisation energyThe periodic table is more than a list of element symbols. It is a map built from atomic number, electron configuration and repeated chemical behaviour. In this lesson you will connect the layout of the table to Period 2 and Period 3 electron configurations, then use first and successive ionisati...
3.1.1(d)-(g) - Giant lattices and melting point trendsElements in the same period can have very different melting points because their particles are arranged and bonded in different ways. In this lesson you will connect metallic bonding, giant covalent lattices and simple molecular lattices to melting point, boiling point, solubility and electrical...
3.1.2(a)-(c) - Group 2 reactivity and ionisation energyMagnesium, calcium, strontium and barium are Group 2 metals. In this lesson you will connect their outer-shell electron configuration to the 2+ ions they form, write their redox reactions with oxygen, water and dilute acids, and explain why their reactivity increases down the group.
3.1.2(d)-(e) - Group 2 oxides, hydroxides and usesGroup 2 oxides and hydroxides are useful because they are basic. In this lesson you will learn how Group 2 oxides react with water, why the resulting solutions become more alkaline down the group, and how selected Group 2 compounds neutralise acids in soils and in the stomach.
3.1.3(a)-(d) - Halogen properties and reactivity trendsThe halogens chlorine, bromine and iodine show two different kinds of trend. Their boiling points increase down the group because the molecules have stronger London forces, but their redox reactivity decreases because they form 1− ions less easily. In this lesson you will learn how to connect obs...
3.1.3(e)-(f) - Disproportionation and chlorine in water treatmentChlorine is reactive enough to take part in an unusual kind of redox reaction: the same element can be oxidised and reduced in one reaction. In this lesson you will learn how to recognise disproportionation using oxidation numbers, write the two key chlorine equations in water and in cold dilute...
3.1.3(g) - Halide ion testsHalide ions are the negative ions made from Group 7 elements: chloride, bromide and iodide. In this lesson you will learn the test-tube reactions used to distinguish aqueous Cl⁻, Br⁻ and I⁻: first with aqueous silver ions, then with aqueous ammonia. The skill is not just remembering colours; it i...
3.1.4 - Inorganic qualitative analysisQualitative analysis is about identifying which ions are present from visible test-tube evidence. In this lesson you will learn the exact OCR sequence for carbonate, sulfate and halide ions, plus the test for ammonium ions. The key skill is to connect a reagent and observation to a secure inferen...
3.2 - Physical chemistry
3.2.1(a)-(d) - Enthalpy profiles and standard enthalpy changesChemical reactions often transfer energy between the reacting chemicals and their surroundings. In this lesson you will learn how to decide whether an enthalpy change is exothermic or endothermic, how to read and construct enthalpy profile diagrams, and how to use the key thermochemistry definiti...
3.2.1(e), 3.2.1(h) - Calorimetry and enthalpy determinationCalorimetry turns a temperature change into an enthalpy change. In this lesson you will learn how to use q = mcΔT, how to scale the energy change to kJ mol⁻¹, and how practical choices affect the result. The aim is not just to get a number: it is to know what the number means, why the sig...
3.2.1(f) - Average bond enthalpiesAverage bond enthalpies let chemists estimate the enthalpy change of a reaction by looking at covalent bonds broken and covalent bonds made. This lesson teaches the exact energy account used in OCR-style questions: bond breaking absorbs energy, bond making releases energy, and the overall enthalp...
3.2.1(g) - Hess' law and enthalpy cyclesSome enthalpy changes are awkward or impossible to measure directly, but they can still be calculated from other enthalpy changes. This lesson teaches the cycle method: compare a direct route with an indirect route, keep the same start and finish, and use signs and coefficients carefully. You do...
3.2.2(a)-(b) - Collision theory and rate graphsReaction rate tells you how quickly a reaction changes a measurable quantity. In this lesson you will connect concentration and gas pressure to collision frequency, then calculate reaction rates from graph gradients. The key skill is to keep the chemistry idea and the graph method joined together...
3.2.2(c)-(e) - Catalysts and rate practicalsCatalysts are used because they make reactions faster without being used up in the overall reaction. In this lesson you will learn how to show catalytic behaviour on an enthalpy profile, how to distinguish homogeneous and heterogeneous catalysts, and how rate practicals collect evidence using mas...
3.2.2(f)-(g) - Boltzmann distributionsBoltzmann distributions help you explain why changing temperature or adding a catalyst can change the rate of reaction. The graph is a model: it shows how molecular kinetic energies are spread out in a sample, and it lets you compare the proportion of molecules with enough energy to react. The ke...
3.2.3(a)-(d) - Dynamic equilibrium and Le Chatelier's principleEquilibrium is what happens when a reversible reaction stops changing in appearance, even though particles are still reacting both ways. In this lesson you will learn how to recognise dynamic equilibrium, predict qualitative shifts when conditions change, and explain why catalysts speed up equili...
3.2.3(e) - Industrial equilibrium compromisesIndustrial equilibrium chemistry is not just about predicting which side of an equilibrium is favoured. In a chemical plant, the conditions must also give a useful reaction rate, be safe to operate, and make economic sense. In this lesson, the Haber process is the main example of how chemists bal...
3.2.3(f)-(g) - Equilibrium constant KcQualitative equilibrium ideas tell you which way a reversible reaction tends to move. The equilibrium constant, Kc, puts a number on the composition of a homogeneous equilibrium mixture at a fixed temperature. In this lesson you will write Kc expressions, calculate Kc from equilibrium...
Core organic chemistry
4.1 - Basic concepts and hydrocarbons
4.1.1(a)-(b) - Organic nomenclature and formula representationsOrganic chemistry uses names and formulae as precise maps of molecules. In this lesson you will learn how a systematic organic name encodes the carbon chain, branches and important groups, and how to move between structural, displayed and skeletal formulae without losing atoms. That skill matters...
4.1.1(c)-(d) - Homologous series and functional groupsOrganic chemistry becomes much easier when molecules are sorted into families. In this lesson you will learn the OCR vocabulary for those families, how to classify carbon skeletons, and how to use a general formula to predict the formula of a member of a homologous series.
4.1.1(e) - Structural isomerismOrganic formulae can be a little deceptive: two compounds may contain exactly the same numbers of each atom, but those atoms may be joined in different ways. In this lesson you will learn the OCR definition of structural isomers and a systematic way to determine possible structural formulae from...
4.1.1(f)-(i) - Covalent fission, radicals and curly arrowsOrganic mechanisms are a way of explaining reactions by following electrons. In this lesson, you will learn how covalent bonds can break, what a radical is, and how OCR expects electron-pair movement to be shown with curly arrows. This is the notation foundation for later organic reactions, so th...
4.1.2(a)-(c) - Alkane structure, shape and physical propertiesAlkanes are the first hydrocarbon family in OCR organic chemistry. In this lesson, you will connect their bonding model to their 3-D shape and then use that structure to explain boiling-point trends. The aim is not just to remember that alkanes are "single-bonded", but to explain why that matters...
4.1.2(d)-(e) - Combustion and low reactivity of alkanesAlkanes look simple, but OCR expects a precise explanation for why they usually react so little and why they are still useful fuels. In this lesson, you will connect their strong, almost non-polar sigma bonds to low reactivity, then compare complete combustion with incomplete combustion in limite...
4.1.2(f)-(g) - Radical substitution of alkanesAlkanes are usually unreactive because their C-C and C-H bonds are strong and non-polar. One important exception is their reaction with chlorine or bromine in ultraviolet radiation, where a hydrogen atom is replaced by a halogen atom through a radical chain reaction. In this lesson, the key is no...
4.1.3(a)-(b), 4.1.3(e) - Alkene bonding, shape and reactivityAlkenes are the first hydrocarbons where a carbon-carbon double bond changes both shape and reactivity. In this lesson, you will build the C=C model from two different bond components, use that model to explain restricted rotation, then connect the shape and bonding to why alkenes react more read...
4.1.3(c)-(d) - Stereoisomerism in alkenesSome alkenes can exist as two different spatial arrangements even though the atoms are connected in the same order. OCR expects you to recognise when this is possible, use the Cahn-Ingold-Prelog priority rules to decide E or Z, and know when the older cis-trans language is safe. The central habit...
4.1.3(f)-(i) - Addition reactions and electrophilic additionAlkenes are useful because the C=C double bond can be turned into several different functional groups. In this lesson, you will learn the addition reactions OCR expects for alkenes, how bromine water tests for unsaturation, why electrophiles react with the double bond, and how Markownikoff's rule...
4.1.3(j)-(l) - Addition polymers and polymer sustainabilityAddition polymers are made when alkene molecules join together to form very long saturated chains. In this lesson, you will learn the two structural skills OCR expects: deducing a repeat unit from an alkene monomer, and working backwards from a polymer section to the monomer. You will then connec...
4.2 - Alcohols, haloalkanes and analysis
4.2.1(a)-(b) - Alcohol properties, classification and combustionAlcohols look a lot like alkanes with one important change: an -OH group has replaced a hydrogen atom. That hydroxyl group makes alcohols polar, able to form hydrogen bonds, and much less volatile than comparable alkanes. In this lesson you will use that same structural idea to explain solubility...
4.2.1(c) - Oxidation of alcoholsAlcohol oxidation is one of the first places where organic chemistry becomes a controlled choice rather than a single fixed reaction. The same primary alcohol can give an aldehyde or a carboxylic acid, depending on the conditions used. In this lesson you will learn how acidified dichromate(VI) ox...
4.2.1(d)-(e) - Elimination and substitution of alcoholsAlcohols are useful because the -OH functional group can be changed into other functional groups. In this lesson, you will learn two OCR routes: eliminating water from an alcohol to make an alkene, and substituting the -OH group using acidified halide ions to make a haloalkane. The exam focus is...
4.2.2(a)-(d) - Haloalkanes and nucleophilic substitutionHaloalkanes are useful because the carbon-halogen bond can be replaced by other groups. In this lesson, the replacement is hydrolysis: a haloalkane forms an alcohol by a substitution reaction. You will learn the reagent conditions, the meaning of nucleophile, the primary haloalkane mechanism, and...
4.2.2(e) - Organohalogens and ozone depletionSome organohalogen compounds are useful because they are chemically stable, but that stability can let them survive long enough to reach the upper atmosphere. In this lesson you will learn how ultraviolet radiation makes radicals from CFCs, how those radicals catalyse ozone breakdown, and why sci...
4.2.3(a) - Organic liquid preparation and purificationPreparing an organic liquid is not just about making a product. The practical skill is to heat the reaction safely, keep volatile substances under control, separate the organic product from water-soluble material, remove traces of water, and finally collect a purer liquid by redistillation. This...
4.2.3(b)-(c) - Two-stage organic synthesisOrganic synthesis is the planning side of organic chemistry: you start with one molecule and choose reactions that turn it into another. In this lesson, you will learn how to recognise several functional groups in the same molecule, predict the reactions each group can undergo, and build two-stag...
4.2.4(a)-(b), 4.2.4(e) - IR absorption, greenhouse gases and usesInfrared spectroscopy begins with a simple idea: covalent bonds can absorb infrared radiation and vibrate more. That idea explains why some atmospheric gases are linked with global warming, and why IR instruments can monitor pollutant gases and measure ethanol in breath. This lesson keeps to the...
4.2.4(c)-(d) - IR spectrum interpretationAn infrared spectrum is evidence about bonds in an organic molecule. In this lesson you will learn how to use the supplied IR data to identify alcohols, aldehydes or ketones, and carboxylic acids from their characteristic absorptions. The skill is not to memorise a whole table; it is to read a sp...
4.2.4(f)-(g) - Organic mass spectrometryMass spectrometry helps chemists identify an organic compound by weighing ions made from its molecules. In this lesson, you will learn how to read the molecular ion peak to find molecular mass, how to avoid being misled by a small M+1 peak, and how fragment peaks can suggest pieces of a structure.
4.2.4(h) - Combined organic analysisOrganic analysis questions are often small detective stories. One piece of data gives a formula, another gives a mass, another gives functional groups, and the correct structure is the one that makes all of them agree. In this lesson you will learn a repeatable OCR-style route for combining eleme...
Physical chemistry and transition elements
5.1 - Rates, equilibrium and pH
5.1.1(a)-(c) - Rate equations, orders and rate constantsRate equations let you turn rate data into a compact mathematical model for a reaction. In this lesson you will learn the required rate terms, use initial-rates data to deduce orders, write rate equations, and calculate the rate constant with its units. The important habit is to let the evidence...
5.1.1(d)-(g) - Concentration-time and rate-concentration graphsGraphs are one of the main ways chemists turn rate data into evidence for reaction order. In this lesson you will learn how to read concentration-time graphs, measure rates from gradients, use constant half-life for first-order reactions, and identify zero-, first- and second-order behaviour from...
5.1.1(h) - Initial rates, continuous monitoring and colorimetryRate experiments turn a visible change into numerical evidence. In this lesson you will learn how chemists measure reaction rates using initial-rate methods, continuous monitoring, and colorimetry, then how those methods feed into the rate graphs and rate equations used elsewhere in 5.1.1. The em...
5.1.1(i) - Rate-determining stepA rate equation is more than a calculation tool: it is experimental evidence about the pathway of a reaction. In this lesson you will use the rate-determining step to connect a multi-step mechanism with the observed rate equation, then work backwards from a rate equation and overall equation to s...
5.1.1(j)-(k) - Arrhenius equation and temperature effectsTemperature changes can make a reaction seem suddenly faster or slower, even when the concentrations have not changed. In this lesson you will connect that observation to the rate constant, k, and then use the Arrhenius equation to turn temperature-rate data into a straight-line graph. The go...
5.1.2(a)-(c) - Equilibrium amounts and partial pressuresEquilibrium calculations begin before the equilibrium constant appears. In this lesson you will learn how to describe the amounts present in an equilibrium mixture, how gas amounts connect to mole fractions and partial pressures, and how chemists can measure equilibrium quantities experimentally....
5.1.2(d)-(e) - Kc and Kp expressions, calculations and unitsEquilibrium constants let you turn an equilibrium mixture into a number. In this lesson you will learn how to write Kc and Kp expressions, how to handle homogeneous and heterogeneous equilibria, and how to calculate values and units without losing the chemistry inside the algebra.
5.1.2(f)-(h) - Equilibrium constants and position of equilibriumEquilibrium constants turn "the equilibrium lies to the right" into a precise chemical idea. In this lesson, you will learn which changes alter the value of an equilibrium constant and which changes only alter the amounts present at equilibrium. The key distinction is simple but often tested: tem...
5.1.3(a)-(c) - Brønsted–Lowry acids, bases and KaAcids and bases are not just substances with certain formulae. At this level, the important model is proton transfer: an acid gives an H⁺ to something that can accept it. This lesson builds that model, uses it to write ionic equations for acid reactions, and introduces Ka and \(...
5.1.3(d)-(f) - pH, Kw and strong acid-base calculationspH is a compact way of communicating very small hydrogen ion concentrations. In this lesson you will turn between pH and [H+], use the ionic product of water, Kw, and calculate pH for strong monobasic acids and strong bases. The main skill is choosing the right ion concentration befo...
5.1.3(g)-(h) - Weak acid pH calculations and approximationsWeak acid calculations are equilibrium calculations written in pH language. You will use Ka, pH and concentration data to find pH, Ka, or a related quantity for a weak monobasic acid. The important skill is knowing exactly when the usual shortcut is sensible, because OCR expects you to un...
5.1.3(i)-(m) - Buffer solutions and blood pHA buffer solution is useful because it keeps the hydrogen ion concentration from changing much when a small amount of acid or base is added. In this lesson, you will learn how an acidic buffer is made, how the conjugate acid-base pair controls pH, how OCR-style buffer calculations use Ka, and...
5.1.3(n)-(o) - pH titration curves, indicators and pH metersA pH titration curve shows how pH changes as one acid-base solution is added to another. In this lesson, you will learn how to read the shape of these curves, choose a suitable indicator from a given pH range, explain indicator colour changes using an acid-base equilibrium, and measure pH accurat...
5.2 - Energy
5.2.1(a)-(b) - Lattice enthalpy and Born-Haber cyclesLattice enthalpy connects the giant ionic lattice from bonding with the energy calculations from Hess' law. In this lesson, you will define lattice enthalpy using OCR's formation convention, build Born-Haber cycles for simple ionic solids, and calculate a missing lattice enthalpy from given data...
5.2.1(c)-(e) - Solution, hydration enthalpy and ionic modelsWhen an ionic solid dissolves in water, two energy ideas compete. Energy is needed to separate ions from the solid lattice, but energy is released when water molecules attract and surround the ions. In this lesson, you will define solution and hydration enthalpies, build the enthalpy cycle that c...
5.2.2(a)-(c) - Entropy and entropy changeEntropy describes how energy is dispersed and helps explain thermodynamic stability when considered alongside enthalpy and conditions. In this lesson, you will learn entropy as a model for energy dispersal and disorder, compare entropy in solids, liquids and gases, and calculate the entropy chang...
5.2.2(d)-(f) - Free energy, feasibility and kinetic limitsSome chemical changes are favoured by energy being released, some by entropy increasing, and many by a balance between the two. This lesson teaches how OCR links those ideas using Gibbs free energy, ΔG, so that you can calculate whether a process is thermodynamically feasible at a state...
5.2.3(a)-(c) - Redox agents, half-equations and predictionsRedox at this stage is about controlling the electron bookkeeping well enough to build equations and make predictions. You already know that oxidation is loss of electrons and reduction is gain of electrons; this lesson turns that into a reliable method for identifying oxidising and reducing agen...
5.2.3(d)-(e) - Redox titrationsRedox titrations use electron transfer to find an unknown amount or concentration. The practical skill is not just "do a titration"; it is choosing the right endpoint signal, using the redox equation for the mole ratio, and processing experimental results without losing the link between the chemi...
5.2.3(f)-(i) - Electrode potentials and feasibilityElectrode potentials let you compare how strongly different redox systems tend to gain electrons. In this lesson, you will learn how standard electrode potentials are measured, how cell potentials are calculated from supplied data, and why a positive prediction still needs practical judgement abo...
5.2.3(j)-(k) - Storage cells and fuel cellsStorage cells and fuel cells are electrochemical cells used as practical sources of electrical energy. In this lesson, you will use supplied electrode-potential data to work out what happens in a modern storage cell, then explain how a fuel cell turns the reaction of a fuel with oxygen into a vol...
5.3 - Transition elements
5.3.1(a)-(c) - Transition element propertiesTransition element chemistry starts with electron configurations. In this lesson, you will learn how to write configurations for Period 4 d-block atoms and ions, decide which of Sc–Zn count as transition elements in OCR Chemistry, and use examples to show their variable oxidation states, coloured...
5.3.1(d)-(e) - Ligands, complex ions and coordination numberTransition metal ions often do not sit alone in solution: they are surrounded by molecules or ions that bond to them using lone pairs. In this lesson, you will learn the exact OCR language for ligands, complex ions and coordination number, then use it to recognise octahedral, tetrahedral and squa...
5.3.1(f)-(g) - Transition metal stereoisomerism and cisplatinTransition metal complexes can have the same atoms bonded in the same order but arranged differently in 3-D space. In this lesson you will learn the two OCR-required types of stereoisomerism in complexes: cis-trans isomerism and optical isomerism. You will then use cis-platin as the key applicati...
5.3.1(h)-(i) - Ligand substitution and haemoglobinLigand substitution is one reason transition-metal chemistry is so visually distinctive: a new ligand can replace an old ligand around a metal ion, forming a new complex with a different colour. In this lesson you will learn the specific copper(II) and chromium(III) substitutions required by OCR,...
5.3.1(j) - Transition metal precipitation reactionsTransition-metal ions in solution often give very distinctive test-tube observations. In this lesson you will learn the precipitation reactions of aqueous Cu²+, Fe²+, Fe³+, Mn²+ and Cr³+ with aqueous sodium hydroxide and aqueous ammonia, then the...
5.3.1(k)-(l) - Transition metal redox and unfamiliar reactionsTransition metal ions often change colour when their oxidation state or ligand environment changes. In this lesson you will learn the OCR-required redox interconversions for iron, chromium and copper, then use half-equations and oxidation numbers to interpret unfamiliar reactions without relying...
5.3.2 - Transition metal qualitative analysisQualitative analysis identifies which ions are present in an unknown compound from test-tube observations. In this lesson you will combine the earlier carbonate, sulfate, halide and ammonium tests with the transition-metal cation tests for Cu²+, Fe²+, Fe³+, \(Mn^..
Organic chemistry and analysis
6.1 - Aromatic compounds, carbonyls and acids
6.1.1(a)-(c) - Benzene models, evidence and aromatic nomenclatureBenzene is the starting point for aromatic chemistry. In this lesson, you will compare the older Kekulé model with the delocalised model, use experimental evidence to decide which model is better, and name simple substituted aromatic compounds using systematic locants.
6.1.1(d)-(g) - Electrophilic substitution of aromatic compoundsAromatic rings react differently from alkenes because their pi electrons are delocalised over the ring. In this lesson you will learn the OCR electrophilic substitution reactions of arenes, the nitration and halogenation mechanisms, and how to use the same pattern when an unfamiliar aromatic subs...
6.1.1(h)-(j) - Phenols, acidity and electrophilic substitutionPhenol looks a little like an alcohol because it contains an OH group, but its chemistry is different because the OH group is attached directly to a benzene ring. In this lesson, you will learn how phenol shows weak acidity, how it reacts with bromine and dilute nitric acid, and why its ring is m...
6.1.1(k)-(l) - Directing effects in aromatic synthesisA substituted benzene ring does not usually react as if every position is equally likely. In this lesson, you will learn how OH, NH₂ and NO₂ groups direct the position of a new electrophilic substitution, and why this matters when chemists plan an aromatic synthesis route.
6.1.2(a)-(c) - Carbonyl reactions and nucleophilic additionCarbonyl compounds contain the C=O group, and that polar double bond controls their reactions. In this lesson, you will learn why aldehydes and ketones are attacked by nucleophiles, how aldehydes are oxidised, and how NaBH₄ or HCN adds to carbonyl compounds. The mechanism detail...
6.1.2(d)-(e) - Carbonyl identification testsCarbonyl tests are a small but high-value part of OCR organic analysis. You will learn how 2,4-dinitrophenylhydrazine detects aldehydes and ketones, how a derivative melting point can identify the particular carbonyl compound, and how Tollens' reagent distinguishes aldehydes from ketones. The exa...
6.1.3(a)-(b) - Carboxylic acid properties and reactionsCarboxylic acids are organic molecules containing the -COOH group. In this lesson you will explain why small carboxylic acids dissolve in water, then use the acidic hydrogen in -COOH to predict reactions with metals and bases in aqueous conditions. The same chemistry als...
6.1.3(c)-(d) - Esterification and ester hydrolysisEsters are made by joining an acid-derived part to an alcohol-derived part, and they are broken apart again by hydrolysis. In this lesson, you will learn the OCR-required esterification routes from carboxylic acids and acid anhydrides, then compare acid and alkaline hydrolysis of esters. The main...
6.1.3(e)-(f) - Acyl chlorides in synthesisAcyl chlorides are reactive carboxylic acid derivatives. In this lesson, you will learn how to make an acyl chloride from a carboxylic acid using SOCl₂, then use the acyl chloride as a short synthetic stepping stone to esters, carboxylic acids, primary amides and secondary amides.
6.2 - Nitrogen compounds, polymers and synthesis
6.2.1 - Basicity and preparation of aminesAmines are organic nitrogen compounds whose reactions are controlled by a lone pair on nitrogen. In this lesson, you will use that lone pair to explain why amines behave as bases, how amines form salts with dilute inorganic acids, and how amines are prepared from haloalkanes or nitroarenes.
6.2.2(a)-(b) - Amino acids and amidesAmino acids contain two reactive functional groups in the same molecule: a carboxylic acid group and an amine group. In this lesson, you will use that structure to predict the OCR-required reactions with alkalis, alcohols and acids. You will also learn how to recognise primary and secondary amide...
6.2.2(c)-(d) - Chirality and optical isomerismSome organic molecules can have the same atoms joined in the same order but still exist as different 3-D arrangements. In this lesson, you will learn optical isomerism as non-superimposable mirror images about a chiral centre, then practise finding chiral centres in condensed and displayed organi...
6.2.3 - Polyesters, polyamides and condensation polymersPolyesters and polyamides are condensation polymers: their chains grow when functional groups react together and a small molecule is eliminated. In this lesson, you will learn how ester and amide links form, how those links are hydrolysed in acid or base, and how to work between monomers, repeat...
6.2.4 - Carbon-carbon bond formationMaking a new C-C bond is one of the most powerful ideas in organic synthesis because it lets chemists build a larger carbon skeleton from a smaller one. In this lesson, you will use cyanide ions, carbonyl compounds and Friedel-Crafts reactions as OCR's required C-C bond-forming routes. The key sk...
6.2.5(a) - Organic solid preparation and purificationOrganic synthesis is only useful if the product can be separated and checked. In this lesson you will learn the practical sequence used for an organic solid: prepare the product safely, isolate the crude solid, purify it by recrystallisation, and use melting point data to judge purity. The focus...
6.2.5(b)-(c) - Multistage organic synthesisMultistage organic synthesis is the skill of planning a route from one organic compound to another. In this lesson, you will learn how to read molecules with several functional groups, predict which reactions are possible, and build routes using transformations from across the OCR specification....
6.3 - Analysis
6.3.1(a)-(b) - ChromatographyChromatography is a family of analytical techniques used to separate and interpret mixtures. In this lesson, the required OCR focus is narrow and practical: one-way TLC chromatograms using Rf values, and gas chromatograms using retention times, peak integration values, proportions and externa...
6.3.1(c) - Organic functional group testsOrganic functional group tests turn small-scale observations into evidence. In this lesson, you will learn the exact OCR test-tube tests for identifying key organic functional groups in an unknown compound. The main skill is not just remembering colours: it is linking reagent, observation and inf...
6.3.2(a) - Carbon-13 NMR spectroscopyCarbon-13 NMR is a structural analysis method for organic molecules. In this lesson you will learn how a carbon-13 spectrum tells you how many different carbon environments are present, how chemical shift values suggest the types of carbon environment, and how to combine those clues to suggest po...
6.3.2(b) - Proton NMR spectroscopyProton NMR spectroscopy lets you use hydrogen atoms as labels inside an organic molecule. In this lesson you will learn how to analyse a high-resolution proton NMR spectrum to predict proton environments, use chemical shift and integration data, apply the n + 1 splitting rule, and build possible...
6.3.2(c)-(d) - Predicting NMR spectra and running NMRNMR is not only a way to identify an unknown molecule. If you already know the structure, you should be able to predict what its carbon-13 and proton NMR spectra would look like. In this lesson, you will turn a molecule into expected NMR signals, then learn why TMS, deuterated solvents and D₂O ar...
6.3.2(e) - Combined spectroscopic structure deductionStructure deduction is the point where the analytical techniques start working as a team. Elemental analysis and mass spectrometry restrict the formula, IR identifies key bonds, and NMR shows how the atoms are arranged into environments and fragments. The skill is not to spot one dramatic peak an...