Why must a dye bond to a fibre rather than simply sit on its surface?

Without bonding the dye would rub off or wash out, so the bonds are what give a dyed fabric its fastness.

Name the three broad kinds of bonding by which dyes attach themselves to fibres.

Intermolecular bonds, ionic bonds and covalent bonds.

State the three types of intermolecular bond that can hold a dye onto a fibre.

Instantaneous dipole–induced dipole bonds, permanent dipole–permanent dipole bonds and hydrogen bonds.

Why are dyes that rely on intermolecular bonding usually long, flat molecules?

A long flat molecule can lie closely alongside the fibre chains, maximising contact so that many intermolecular bonds form.

Which groups on a dye and on cotton allow hydrogen bonding between them?

–OH and –NH₂ groups on the dye hydrogen bond to the –OH groups of the cellulose chains in cotton.

Explain why a dye held only by instantaneous dipole–induced dipole bonds washes out readily.

Each such bond is weak, so water molecules competing for the fibre and for the dye can easily pull the dye away.

OCR A-Level Chemistry B H433

Development of Practical Skills in Chemistry

Topic overview Planning experiments Implementing: apparatus, units and recording data Significant figures and titration calculations Graphs, gradients and drawing a conclusion Anomalous results, precision, accuracy and types of error Calculating uncertainties and improving a method Hazards, risk and control measures Recording, processing and judging data Measuring pH, mass and volume, and choosing an indicator Reflux, distillation, purification and the standard tests PAG1 to PAG6: moles, enthalpy, qualitative analysis and organic synthesis PAG7 to PAG12: electrochemistry, rates and pH

Elements of Life

Topic overview The mole, relative masses and empirical formulae Concentration, titration and writing balanced equations Orbitals, sub-shells and electron configurations Sub-atomic particles and the evidence for the model of the atom Fusion reactions and the origin of the elements Ionic, covalent, dative and metallic bonding and the four structures Melting point, conductivity and solubility of each structure Shapes of molecules and ions The periodic table, the blocks and trends in melting point Ion charges, the common polyatomic ions and writing formulae Group 2 chemistry and charge density Ionisation enthalpy and trends in reactivity Solubility rules and the tests for the common anions Hydroxide precipitates, ionic equations and identifying an unknown salt Acids, bases and preparing salts The electromagnetic spectrum and photon energy calculations Emission and absorption spectra, and flame tests Mass spectrometry and relative atomic mass

Developing Fuels

Topic overview Molar gas volume and the ideal gas equation Gas volume calculations and measuring a gas in the laboratory Bonding and shape in organic molecules Enthalpy changes: definitions and standard conditions Bond enthalpies q = mcΔT and measuring an enthalpy change in solution Burning a fuel, correcting for heat loss, and the assumptions made Hess' law and enthalpy cycles Catalysts, heterogeneous catalysis and catalyst poisons Cracking and how it is carried out The pollutants from burning fuels and their effects Catalytic converters and cutting emissions Aliphatic and aromatic compounds, functional groups and general formulae Deducing formulae and naming a branched compound Combustion of organic compounds Addition of bromine and hydrogen halides, and the test for unsaturation Hydrogenation and hydration of alkenes Addition polymerisation Electrophilic addition mechanism Displayed, shortened and skeletal formulae Chain, position and functional group isomerism Why alkenes show stereoisomerism, and the E/Z and cis/trans rules Naming and comparing the stereoisomers Sustainable fuels: benefits and risks

Elements From the Sea

Topic overview Atom economy Extraction of the halogens from sea minerals Electrolysis of molten salts and writing electrode half-equations Electrolysis of aqueous solutions and the electrolysis of brine Redox as electron transfer The rules for assigning oxidation states Oxidation state calculations, and defining oxidation and reduction Balancing a redox equation with oxidation states The iodine-thiosulfate titration and its calculations Systematic nomenclature of inorganic compounds Physical properties of the halogens Halogen reactivity and the displacement equations Observing a displacement, and using an organic solvent or starch Silver halide precipitation and tests Preparation of the hydrogen halides Properties of the hydrogen halides Chlorine: risks, benefits and uses Dynamic equilibrium Writing a Kc expression and calculating Kc What the magnitude of Kc tells you, and what changes it Using the Kc expression to explain a shift in position Temperature, pressure and catalysts on an equilibrium

The Ozone Story

Topic overview Electronegativity and bond polarity Intermolecular bonds Boiling points and intermolecular bonds Activation enthalpy and enthalpy profiles Collision theory and the Boltzmann distribution Following a reaction and finding the rate from a graph Catalysts and alternative reaction routes Homogeneous catalysis and intermediates Composition of gas mixtures by volume Recognising and naming haloalkanes Primary, secondary and tertiary haloalkanes, and the amines Properties and nucleophilic substitution of haloalkanes Substitution, nucleophiles and the SN2 mechanism Relative reactivity of the haloalkanes Homolytic and heterolytic fission, radicals and half curly arrows Initiation, propagation and termination in a radical chain reaction Ozone depletion by haloalkanes Ozone in the stratosphere and troposphere Radiation of the Earth and the Sun Effects of UV and visible radiation on molecules Calculations with frequency, wavelength and energy

What's in a Medicine?

Topic overview Formulae of oxygen-containing homologous series Primary, secondary and tertiary alcohols The acidity of phenol compared with alcohols and carboxylic acids The iron(III) chloride test and esterifying a phenol Esterification and oxidising primary, secondary and tertiary alcohols Dehydration, halogenation and planning a two-step synthesis Preparing aspirin, filtering under reduced pressure and recrystallisation Thin layer chromatography, Rf values and percentage yield Reflux and distillation in an organic preparation Washing, drying and redistilling a liquid product The aims of green chemistry and atom economy Catalysts, renewable feedstocks and measuring greenness Elimination reactions The molecular ion and fragment ions Identifying a compound from its fragments and the M+1 peak How infrared absorption works and the characteristic absorptions Reading a spectrum, the fingerprint region and combining techniques

The Chemical Industry

Topic overview Rate equations, order and the rate constant Deducing the units of k and rate calculations Half-lives Continuous monitoring, quenching and the initial rates method Reading order from concentration-time and rate-concentration graphs The Arrhenius equation and what each symbol means The ln k against 1/T plot and finding the activation enthalpy Rate-determining step and mechanism Effect of conditions on the magnitude of the equilibrium constant Economic operating conditions for an industrial process Writing a Kc expression and deducing its units ICE-table calculations and measuring Kc experimentally Chemical reactions in industrial processes Nitrogen, ammonia and the ammonium ion Oxidation states of nitrogen and the tests for nitrate and ammonium Costs, benefits and risks of industrial processes

Polymers and Life

Oceans

Topic overview Solubility in aqueous and non-aqueous solvents Lattice, hydration and solution enthalpies and how they relate Measuring an enthalpy change of solution Charge density and the size of enthalpy terms Entropy: qualitative treatment Total entropy change and the condition for feasibility The limiting temperature, and why a feasible reaction may not happen Calculating the entropy change of the system The solubility product expression, its units and calculations Predicting precipitation and the common ion effect Bronsted-Lowry theory of acids and bases Strong acids and strong bases Weak acids, Ka and pKa pH of strong acids and strong bases pH of weak acids, dilution and the limits of the approximation What a buffer is and how it resists a change in pH Buffer calculations, capacity and the natural buffers How the greenhouse effect works and which gases cause it Why a molecule absorbs, concentrations in ppm, and ocean chemistry

Developing Metals

Topic overview Manganate(VII) titrations and their calculations Thiosulfate titrations, recording results and good technique Shapes of complexes and coordination number Balancing redox equations involving acid-base reactions Simple electrochemical cells Action of an electrochemical cell Standard electrode potentials and calculating E°cell Rusting and how it is prevented Transition metals: definition, oxidation states and colours d-block electron configurations of the atoms and their ions Why transition metals show variable oxidation states Ligands and complex ions Coordinate bonding and what makes a ligand Bidentate and multidentate ligands, and finding a complex's formula Reactions of Fe2+, Fe3+ and Cu2+ with hydroxide and ammonia Catalytic activity of transition metals Origin of colour in transition metal complexes Colorimetry

Colour by Design

Topic overview How dyes attach to fibres Structure of a dye molecule Fats and oils Arenes and delocalisation Representations of benzene and enthalpy of hydrogenation Tests for the common functional groups Identifying a polyfunctional molecule from a set of test results Halogenation and nitration of benzene and the electrophiles involved The nitration mechanism, sulfonation and the Friedel-Crafts reactions Diazotisation and why it is done cold Coupling reactions, azo dyes and the route from benzene Oxidising an aldehyde and the three carbonyl tests Cyanohydrin formation and its use in synthesis Using the Data Sheet reactions to plan a route Choosing between routes on yield and atom economy Nucleophilic addition mechanism Classifying organic reactions and unfamiliar mechanisms Origins of colour in organic molecules How gas-liquid chromatography separates a mixture Retention time, peak area and the limits of the technique

Chemical Literacy

Topic overview Extracting and using data and information from a scientific text Written communication and comprehension

Mathematical Skills in Chemistry

Topic overview Units, standard form and the mole in calculations Yield, atom economy and logarithmic quantities Significant figures, means and handling data Symbols, and rearranging the standard equations Substituting into rearranged equations Reading spectra and kinetics graphs Gradients, calibration lines and the Arrhenius plot Shapes and bond angles from electron pair repulsion Chiral centres, E/Z isomerism and optical activity

Colour by Design

20 subtopics
45 things to know
Components 01, 02 and 03

What Colour by Design covers

The final storyline, which carries the arenes and the rest of the organic chemistry: how a dye attaches to a fibre, fats and oils, benzene and electrophilic substitution, azo dyes, the carbonyl compounds, planning a synthetic route, why organic molecules are coloured, and gas-liquid chromatography.

Where it is assessed

Components 01, 02 and 03

Storyline content, drawn on by all three written papers.

Check the OCR specification ↗

The 20 subtopics

Each one has its own page.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Process

Why must a dye bond to a fibre, why are such dyes long and flat, and why do the weakest-bound ones wash out?

Process

Wool and nylon take acid dyes well but polyester does not. Explain why.

Key term

Why are fibre-reactive dyes the most wash-fast of all?

Process

What does an NH₂ group do to a conjugated system, why does an NO₂ group deepen the colour of an azo dye, and why can too many solubilising groups be a problem?

Process

Which groups let a dye hydrogen bond to a fibre, why is a dye molecule best seen as several parts, and why does adding a sulfonate group hardly change the colour?

Numbers

State the structural feature common to almost all azo dyes.

Key term

What is a fatty acid, what structural difference separates a fat from an oil, and which is solid at room temperature?

Key term

What is the difference between a monounsaturated and a polyunsaturated chain, and what test shows an oil is unsaturated?

Key term

How is a liquid oil hardened industrially, and what does hydrolysing a fat with alkali and with acid give?

Numbers

What is an arene, and what are the molecular and empirical formulae of benzene and the formula of methylbenzene?

Numbers

What are the formulae of phenylamine and benzoic acid, and what is meant by an aromatic compound?

Numbers

What is delocalisation, why does cyclohexene decolourise bromine water when benzene does not, and what does benzene give with bromine over a halogen carrier?

Key term

State the bond angle at each carbon atom in benzene.

Numbers

Two isolated double bonds would predict an enthalpy change of hydrogenation of what value for cyclohexa-1,3-diene, and what is found?

Key term

Why does the hydrogenation of benzene need more forcing conditions than that of cyclohexene?

Key term

Which reagent tests for a C=C bond, how is a carboxylic acid told apart from a phenol in a test tube, and why does sodium hydroxide not distinguish them?

Key term

What is seen with a carboxylic acid and magnesium, and why does acidified dichromate not separate an aldehyde from a primary alcohol?

Key term

Which alcohol gives no colour change with dichromate, what is seen when an acyl chloride meets water, and which test makes a new ester?

Key term

Why should functional group tests be carried out one at a time, with observations recorded before the next reagent is added?

Key term

Name the organic product and a suitable catalyst for the chlorination of benzene.

Numbers

Why is the temperature of a nitration kept near 50 °C?

Numbers

Which compound starts a diazonium salt, why is nitrous acid made in the mixture, and what is the formula of benzenediazonium chloride?

Numbers

Where does coupling occur on a phenol ring, which group joins the two rings, and what is an azo dye?

Key term

Why must alkali be added after the tin and hydrochloric acid reduction?

Key term

What is observed when a cold diazonium solution is run into alkaline phenol solution?

Numbers

What do ethanal and propanal give on oxidation, and what colour change accompanies it?

Process

Why are ketones not oxidised by acidified dichromate, what is Tollens' reagent, and what does an aldehyde do to it?

Numbers

What does ethanal give with Tollens', which species is reduced, and what does a ketone do with Tollens' and Fehling's?

Process

Explain how the three carbonyl tests work together to place an unknown compound.

Numbers

What conditions hydrolyse a nitrile, which acid comes from bromoethane by that route, and what does NaBH₄ do?

Numbers

What does NaBH₄ give with propanone, why convert an acid to its acyl chloride, and what do tin and hydrochloric acid do to a nitroarene?

Numbers

Adding HCN to ethanal has an atom economy of 100%, while CH₃CH₂Br + KCN → CH₃CH₂CN + KBr has 31.6%. Why might a chemist still choose the cyanide substitution route?

Numbers

What is a nucleophile, why is the carbonyl carbon electron-deficient, and what partial charges does the group carry?

Numbers

What does ethanal give with hydrogen cyanide, and why is the reaction classed as nucleophilic addition?

Process

Where must a curly arrow begin, why does cyanide addition to an unsymmetrical carbonyl give two optical isomers, and how do alkenes and carbonyl compounds differ in how their additions start?

Key term

What is always lost from the reactant molecule in an elimination, and what feature appears in the product?

Numbers

What happens when a molecule absorbs a visible photon, and how is the energy related to frequency and wavelength?

Process

Which part of a molecule absorbs, what does extending the delocalisation do, and why is extensive delocalisation needed for colour?

Process

What is conjugation, what does an NH₂ group do to it, and which of dye A (absorbing at 430 nm) and dye B (at 520 nm) has the more extended delocalisation?

Numbers

Why does an intensely coloured dye give a strong colour even at very low concentration?

Key term

Why is the injection port heated, which component leaves the column first, and what is retention time?

Evaluation

State the main limitation of identifying a compound by retention time alone.

Evaluation

How is the limitation of identifying a compound by retention time alone overcome in modern instruments?

Key term

What is formed when benzene is hydrogenated completely?

Key term

State the conditions used to react a halogenoalkane with cyanide ions.

Take Colour by Design further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

Chromophore vs Solubilising group
Chromophore: the delocalised part of a molecule responsible for absorbing visible light. Solubilising group: a polar group attached to a dye so that it dissolves and bonds to the fibre.
Electrophilic substitution vs Electrophilic addition
Electrophilic substitution: the characteristic reaction of arenes, in which a hydrogen atom is replaced. Electrophilic addition: the characteristic reaction of alkenes, in which the double bond opens.
Friedel-Crafts alkylation vs Friedel-Crafts acylation
Friedel-Crafts alkylation: attaching an alkyl group to a benzene ring using a haloalkane and a halogen carrier. Friedel-Crafts acylation: attaching an acyl group to a benzene ring using an acyl chloride and a halogen carrier.

Questions from this topic

Each one with the model answer underneath.

1
Why must a dye bond to a fibre rather than simply sit on its surface?
Model answer
Without bonding the dye would rub off or wash out, so the bonds are what give a dyed fabric its fastness.
2
Name the three broad kinds of bonding by which dyes attach themselves to fibres.
Model answer
Intermolecular bonds, ionic bonds and covalent bonds.
3
State the three types of intermolecular bond that can hold a dye onto a fibre.
Model answer
Instantaneous dipole–induced dipole bonds, permanent dipole–permanent dipole bonds and hydrogen bonds.
4
Why are dyes that rely on intermolecular bonding usually long, flat molecules?
Model answer
A long flat molecule can lie closely alongside the fibre chains, maximising contact so that many intermolecular bonds form.
5
Which groups on a dye and on cotton allow hydrogen bonding between them?
Model answer
–OH and –NH₂ groups on the dye hydrogen bond to the –OH groups of the cellulose chains in cotton.
6
Explain why a dye held only by instantaneous dipole–induced dipole bonds washes out readily.
Model answer
Each such bond is weak, so water molecules competing for the fibre and for the dye can easily pull the dye away.

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Development of Practical Skills in Chemistry

Elements of Life

Developing Fuels

Elements From the Sea

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A acid is formed.

carboxylicnitricfatty

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A3 ⁴₂He → ¹²₆C.

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Nitrogen is +2 in NO and +4 in NO₂.

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Colour by Design revision questions

What does Colour by Design cover in OCR A-Level Chemistry B?: 20 subtopics: how dyes attach to fibres, structure of a dye molecule, fats and oils, arenes and delocalisation, representations of benzene and enthalpy of hydrogenation, tests for the common functional groups, identifying a polyfunctional molecule from a set of test results, halogenation and nitration of benzene and the electrophiles involved, the nitration mechanism, sulfonation and the friedel-crafts reactions, diazotisation and why it is done cold, coupling reactions, azo dyes and the route from benzene, oxidising an aldehyde and the three carbonyl tests, cyanohydrin formation and its use in synthesis, using the data sheet reactions to plan a route, choosing between routes on yield and atom economy, nucleophilic addition mechanism, classifying organic reactions and unfamiliar mechanisms, origins of colour in organic molecules, how gas-liquid chromatography separates a mixture and retention time, peak area and the limits of the technique. Each one has its own page with questions and model answers.
How is Colour by Design organised?: By the OCR H433 specification, subtopic by subtopic, so it matches the order you are taught it in.

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