Define refluxing as a laboratory technique.

Heating a reaction mixture continuously while vapours are condensed by a vertical condenser and returned to the flask, allowing prolonged heating without loss of volatile components.

What is purification by washing in organic synthesis?

Shaking the organic product with aqueous solutions in a separating funnel to remove water-soluble impurities.

Define solvent extraction.

A technique using a separating funnel to partition a compound between two immiscible solvents based on the compound's relative solubility in each solvent.

What happens during the cooling stage of recrystallisation?

The solution becomes supersaturated and pure crystals form slowly, while impurities remain dissolved in the solvent.

Edexcel A-Level Chemistry 9CH0

Atomic Structure and the Periodic Table

Topic overview Protons, neutrons, electrons and isotopes Relative atomic mass and the mass spectrum Ionisation energy and the evidence for sub-shells Orbitals and electron configuration Periodicity across a period and down a group

Bonding and Structure

Topic overview Ionic bonding Covalent bonding, dative bonding and the shapes of molecules Electronegativity, polarity and intermolecular forces Structure and properties

Redox I

Topic overview Oxidation numbers Oxidation, reduction, disproportionation and half-equations

Inorganic Chemistry and the Periodic Table

Topic overview Flame tests and how they work Thermal decomposition of nitrates and carbonates Carrying out flame tests and testing the gases Group 2 elements and their compounds Trends in Group 7 and predicting fluorine and astatine Halogen displacement reactions Disproportionation and the reactions of chlorine Halides with concentrated sulfuric acid, and the hydrogen halides Testing for halide ions with silver nitrate Testing for carbonate and hydrogencarbonate ions Testing for sulfate and ammonium ions

Formulae, Equations and Amounts of Substance

Topic overview The mole, molar mass and empirical formula The ideal gas equation and molar volume Equations, concentration and reacting quantities Standard solutions, titration and uncertainty Percentage yield, atom economy and acid reactions Core practicals 1 to 3 Empirical formula and water of crystallisation by experiment Apparatus, uncertainty and mathematical skills

Organic Chemistry I

Topic overview Formulae, homologous series and functional groups IUPAC nomenclature Types of organic reaction and structural isomerism Stereoisomerism and E/Z nomenclature Practical techniques in organic chemistry Alkanes, crude oil and combustion pollutants Radical substitution Alkenes, the double bond and hydrogenation Electrophilic addition, Markovnikov's rule and the test for an alkene Addition polymers and waste polymers Nucleophilic substitution of halogenoalkanes Rates of hydrolysis and the SN1 and SN2 mechanisms Classifying and oxidising alcohols Alcohols: practical techniques and the core practicals

Modern Analytical Techniques I

Topic overview Mass spectrometry Infrared spectroscopy and the characteristic absorptions Deducing functional groups from an infrared spectrum

Energetics I

Topic overview Enthalpy changes, standard definitions and calorimetry Hess's law and bond enthalpies

Kinetics I

Topic overview Collision theory and factors affecting rate Maxwell-Boltzmann distribution and temperature Catalysts, reaction profiles and measuring rate

Equilibrium I

Topic overview Dynamic equilibrium and Le Chatelier's principle The equilibrium constant Kc

Equilibrium II

Topic overview Partial pressures and Kp Calculating Kp and the effect of conditions

Acid-Base Equilibria

Topic overview Bronsted-Lowry acids and bases, and the pH scale Strong and weak acids, Ka and Kw Calculating pH, and titration curves Buffer solutions and the Henderson-Hasselbalch equation Buffers in blood, and the core practical

Energetics II

Topic overview Lattice energy Born-Haber cycles and electron affinity Entropy and the direction of change Gibbs free energy and thermodynamic feasibility

Redox II

Topic overview Standard electrode potentials and the hydrogen electrode Electrochemical cells, emf and cell diagrams Feasibility, the electrochemical series and disproportionation Storage cells, fuel cells and redox titrations

Transition Metals

Topic overview Electron configuration and what makes a transition metal Complex ions, ligands and the colour of transition metal ions Coordination number, monodentate ligands and the shapes of complexes Bidentate and multidentate ligands, and ligand exchange Vanadium and chromium chemistry Reactions with sodium hydroxide and ammonia Cobalt and copper complexes Ligand exchange, amphoteric behaviour and the chelate effect Transition metals as catalysts

Kinetics II

Topic overview Rate equations, orders and the rate constant Determining orders from experiments Rate-determining step and mechanisms Arrhenius equation and activation energy

Organic Chemistry II

Topic overview Chirality Aldehydes, ketones and their oxidation Reduction and nucleophilic addition of HCN Testing for a carbonyl group: 2,4-DNPH and the iodoform reaction Carboxylic acids and their reactions Esters and acyl chlorides Reflux, extraction and recrystallisation Distillation, melting temperature and working safely

Organic Chemistry III

Topic overview The structure of benzene and the evidence for it Electrophilic substitution of benzene Nitration, halogenation, Friedel-Crafts and phenol Amines: structure and basicity Reactions of amines and preparing them Amides and condensation polymers Amino acids, zwitterions and proteins Empirical and molecular formulae from analytical data Grignard reagents and multi-step synthesis Purification techniques and the aspirin preparation

Modern Analytical Techniques II

Topic overview Carbon-13 and proton NMR Splitting, integration and the reference standard Chromatography High-resolution mass spectrometry

Organic Chemistry III

Purification techniques and the aspirin preparation

3 things to know
Papers 2 and 3

Overview

Reflux, washing, solvent extraction, recrystallisation and drying, simple and steam distillation, judging purity from melting and boiling temperatures, and preparing aspirin by acetylating 2-hydroxybenzoic acid with ethanoic anhydride, then purifying it and checking its purity.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

During recrystallisation, why might hot filtration be performed before cooling?

Key term

How is crude aspirin purified after synthesis, and how is its purity assessed?

Key term

In recrystallisation, why is the impure solid dissolved in a minimum volume of hot solvent?

Questions from this subtopic

Each one with the model answer underneath.

1
Define refluxing as a laboratory technique.
Model answer
Heating a reaction mixture continuously while vapours are condensed by a vertical condenser and returned to the flask, allowing prolonged heating without loss of volatile components.
2
What is purification by washing in organic synthesis?
Model answer
Shaking the organic product with aqueous solutions in a separating funnel to remove water-soluble impurities.
3
Define solvent extraction.
Model answer
A technique using a separating funnel to partition a compound between two immiscible solvents based on the compound's relative solubility in each solvent.
4
In recrystallisation, why is the impure solid dissolved in a minimum volume of hot solvent?
Model answer
To ensure the solution is saturated, so that upon cooling, the maximum amount of pure product crystallises out.
5
During recrystallisation, why might hot filtration be performed before cooling?
Model answer
To remove any insoluble impurities that would otherwise contaminate the crystals.
6
What happens during the cooling stage of recrystallisation?
Model answer
The solution becomes supersaturated and pure crystals form slowly, while impurities remain dissolved in the solvent.

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Atomic Structure and the Periodic Table

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Inorganic Chemistry and the Periodic Table

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