6.10.2

Thin-Layer Chromatography (A2 Only)

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Thin-Layer Chromatography

Thin-layer chromatography (TLC) is a type of chromatography used to identify and separate chemicals in a mixture.

1) Setup the apparatus

1) Setup the apparatus

  • Use an aluminium TLC plate coated in silica or alumina.
  • The substances to be separated or identified must be dissolved in organic solvent and dotted along the bottom of the TLC plate.
  • The TLC plate is placed in a closed jar with a small amount of organic solvent inside.
2) Run the experiment

2) Run the experiment

  • The jar is left and the organic solvent in the jar rises up the TLC plate and over the dots.
  • The TLC plate is removed when the solvent front (top of the rising solvent on the plate) nears the top edge of the plate.
  • We can now use this TLC plate to either identify or separate the components in the mixture.
3) Evaluate the results

3) Evaluate the results

  • The mobile phase is the organic solvent (typically apolar).
  • The stationary phase is the TLC plate (typically polar).
    • The more polar substances will interact more with the stationary phase and so will be found lower down the plate.
    • The less polar substances will interact more with the mobile phase and so will rise with the solvent more quickly and will be found higher up the plate.

Separation and Identification

TLC can be used to separate and identify substances in mixtures.

Separation

Separation

  • When separation is required, substances from the mixture can be isolated by cutting up regions with just one spot from the TLC plate.
R<sub>f</sub> values

Rf values

  • We use Rf values to identify substances. These values are calculated as:
    • Rf = distance travelled by substance ÷ distance travelled by solvent
  • We can calculate the Rf value for reference substances and the tested substances.
Identification

Identification

  • Rf values depend on the solvent that they are measured in.
  • The identification process is comparing the Rf value of the reference and tested substance.
Calculation of R<sub>f</sub>

Calculation of Rf

  • We have a mixture and we suspect that it contains a particular component e.g. propanol.
  • Since Rf values are relative to the conditions, we must only compare values measured under the same conditions.
    • The best way to do this is to add a spot of the suspected component, e.g. propanol, to the same TLC plate as the mixture and run them together, then we can see if the Rf values align.
    • If the Rf values do align, there's significant evidence that the suspected component is in the mixture.

Colourless Chemicals

Some chemicals used in TLC can't be identified because they aren't visible on the TLC plate. The following are methods for locating these colourless chemicals:

Fluorescent dyes

Fluorescent dyes

  • Fluorescent dyes are visible when UV light is shone on them.
    • This allows us to see where the spot of the colourless chemical is and so we can calculate its Rf value.
Iodine

Iodine

  • Iodine turns the colourless spots purple.
    • This is another method that allows us to see where the spot of the colourless chemical is so that we can calculate its Rf value.
Jump to other topics
1

Physical Chemistry

1.1

Atomic Structure

1.1.1Fundamental Particles1.1.2Isotopes & Mass Number1.1.3Mass Spectrometry1.1.4Electron Shells, Sub-Shells & Orbitals1.1.5Electron Configuration1.1.6Ionisation Energy1.1.7Factors Affecting Ionisation Energies1.1.8Trends of Ionisation1.1.9Specific Impacts on Ionisation Energies1.1.10End of Topic Test - Atomic Structure1.1.11A-A* (AO3/4) - Atomic Structure
1.2

Amount of Substance

1.2.1Relative Masses1.2.2The Mole1.2.3The Ideal Gas Equation1.2.4Empirical & Molecular Formulae1.2.5Balanced Equations1.2.6Percentage Yield1.2.7A-A* (AO3/4) - Percentage Yield1.2.8Atom Economy1.2.9End of Topic Test - Amount of Substance1.2.10A-A* (AO3/4) - Substances & Yield1.2.11Diagnostic Misconceptions - Moles
1.3

Bonding

1.3.1Ionic Bonding1.3.2Covalent & Dative Bonding1.3.3Carbon Structures1.3.4Metallic Bonding1.3.5Physical Properties1.3.6Shapes of Molecules1.3.7Polarity1.3.8Intermolecular Forces1.3.9Intermolecular Forces 21.3.10End of Topic Test - Bonding1.3.11Exam-Style Question - Shape of Molecules1.3.12A-A* (AO3/4) - Bonding1.3.13Diagnostic Misconceptions - Ions1.3.14Diagnostic Misconceptions - Ionic & Covalent1.3.15Diagnostic Misconceptions - Phase Change1.3.16Diagnostic Misconceptions - Boiling1.3.17Diagnostic Misconceptions - Polar Bonds
1.4

Energetics

1.4.1Enthalpy Changes1.4.2Bond Breaking and Making1.4.3Enthalpy Changes: Standard Conditions1.4.4Calorimetry1.4.5Hess' Law1.4.6Bond Enthalpies1.4.7End of Topic Test - Energetics1.4.8Diagnostic Misconceptions - Calorimetry
1.5

Kinetics

1.5.1Collision Theory1.5.2Maxwell-Boltzmann Distribution1.5.3Increasing Rates1.5.4End of Topic Test - Kinetics
1.6

Equilibria

1.6.1Le Chatelier1.6.2Equilibrium Constants1.6.3A-A* (AO3/4) - Energetics, Kinetics, Equilibria1.6.4End of Topic Test - Equilibria1.6.5Diagnostic Misconceptions - Solids
1.7

Redox

1.7.1Redox1.7.2End of Topic Test - Redox
2

Physical Chemistry 2 (A2 Only)

2.1

Thermodynamics (A2 Only)

2.1.1Born-Haber Cycles (A2 Only)2.1.2Born-Haber Cycle Calculations (A2 Only)2.1.3Entropy (A2 Only)2.1.4Free Energy (A2 Only)2.1.5End of Topic Test - Thermodynamics2.1.6A-A* (AO3/4) - Thermodynamics
2.2

Rate Equations (A2 Only)

2.2.1Rate Equations (A2 Only)2.2.2Rate Equations 2 (A2 Only)2.2.3The Arrhenius Equation (A2 Only)2.2.4Experimental Methods for Rates (A2 Only)2.2.5End of Topic Test - Rate Equations2.2.6Exam-Style Question - Rates2.2.7A-A* (AO3/4) - Rate Equations
2.3

The Equilibrium Constant Kp (A2 Only)

2.3.1Properties of Kp (A2 Only)
2.4

Electrochemical Cells (A2 Only)

2.4.1Electrochemical Cells (A2 Only)2.4.2Electrochemical Series (A2 Only)2.4.3Commercial Application (A2 Only)2.4.4End of Topic Test - Kp & Electrochemistry2.4.5A-A* (AO3/4) - Electrochemical Cells2.4.6Diagnostic Misconceptions - Salt Bridges2.4.7Diagnostic Misconceptions - Electrode, Electrolyte
2.5

Acids & Bases (A2 Only)

2.5.1Brønsted-Lowry Acids & Bases (A2 Only)2.5.2pH (A2 Only)2.5.3The Ionic Product of Water (A2 Only)2.5.4Weak Acids & Bases (A2 Only)2.5.5pH Curves & Titrations (A2 Only)2.5.6pH Curves & Titrations 2 (A2 Only)2.5.7Buffer Solutions (A2 Only)2.5.8End of Topic Test - Acids & Bases2.5.9Exam-Style Question - Weak Acids2.5.10A-A* (AO3/4) - Acids & Bases2.5.11Diagnostic Misconceptions - Ammonia is an Alkali2.5.12Diagnostic Misconceptions - Water's Neutrality2.5.13Diagnostic Misconceptions - Concentrate & Strength
3

Inorganic Chemistry

3.1

Periodicity & Trends

3.1.1The Periodic Table3.1.2Trends in the Periodic Table3.1.3End of Topic Test - Periodicity & Trends3.1.4Diagnostic Misconceptions - Atomic Radius
3.2

Group 2

3.2.1Group 2 Chemistry3.2.2End of Topic Test - Group 2
3.3

Group 7

3.3.1Introduction to Halogens3.3.2Reactions of Halogens3.3.3Chlorine & Chlorate(I)3.3.4End of Topic Test - Group 73.3.5Exam-Style Question - Group 73.3.6A-A* (AO3/4) - Periodicity, Group 2 & 7
4

Inorganic Chemistry 2 (A2 Only)

4.1

Period 3 (A2 Only)

4.1.1Period 3 Elements & Oxides (A2 Only)4.1.2Period 3 Oxides (A2 Only)4.1.3End of Topic Test - Period 3
4.2

Transition Metals (A2 Only)

4.2.1General Properties (A2 Only)4.2.2Substitution Reactions (A2 Only)4.2.3Shapes of Complex Ions (A2 Only)4.2.4Colours of Ions (A2 Only)4.2.5Variable Oxidation States (A2 Only)4.2.6Titrations (A2 Only)4.2.7Homogeneous Catalysts (A2 Only)4.2.8Heterogeneous Catalysts (A2 Only)4.2.9End of Topic Test - Transition Metals4.2.10A-A* (AO3/4) - Transition Metals
4.3

Reactions of Ions in Aqueous Solutions (A2 Only)

4.3.1Acidity (A2 Only)4.3.2Identification (A2 Only)4.3.3End of Topic Test - Reactions of Ions in Solution
5

Organic Chemistry 1

5.1

Introduction

5.1.1Naming Conventions5.1.2Mechanism5.1.3Isomerism5.1.4End of Topic Test - Introduction to Organic Chem
5.2

Alkanes

5.2.1Fractional Distillation5.2.2Cracking5.2.3Combustion5.2.4Chlorination5.2.5End of Topic Test - Alkanes
5.3

Halogenoalkanes

5.3.1Substitution Reactions5.3.2Elimination Reactions5.3.3Ozone Depletion5.3.4End of Topic Test - Halogenoalkanes
5.4

Alkenes

5.4.1Introduction to Alkenes5.4.2Reactions of Alkenes5.4.3Polymerisation Reactions5.4.4Properties of Polymers5.4.5End of Topic Test - Alkenes
5.5

Alcohols

5.5.1Production of Alcohols5.5.2Oxidation of Alcohols5.5.3Oxidation of Alcohols - 25.5.4Elimination Reactions5.5.5End of Topic Test - Alcohols5.5.6Exam-Style Question - Alcohols
5.6

Organic Analysis

5.6.1Reactions5.6.2Reactions 25.6.3Mass Spectrometry5.6.4Infrared Spectroscopy5.6.5End of Topic Test - Organic Analysis
5.7

A-A* (AO3/4) - Organic 1

5.7.1A-A* (AO3/4) - Organic 1
6

Organic Chemistry 2 (A2 Only)

6.1

Optical Isomerism (A2 Only)

6.1.1Optical Isomerism (A2 Only)6.1.2End of Topic Test - Optical Isomerism
6.2

Aldehydes & Ketones (A2 Only)

6.2.1Aldehydes & Ketones (A2 Only)6.2.2End of Topic Test - Aldehydes & Ketones
6.3

Carboxylic Acids & Esters (A2 Only)

6.3.1Acids & Esters (A2 Only)6.3.2Acylation (A2 Only)6.3.3End of Topic Test - Carboxylic Acids & Esters
6.4

Aromatic Chemistry (A2 Only)

6.4.1Structure & Reactivity (A2 Only)6.4.2Reactions of Benzene (A2 Only)6.4.3End of Topic Test - Aromatic Chemistry
6.5

Amines (A2 Only)

6.5.1Nature & Preparation of Amines (A2 Only)6.5.2Basicity & Nucleophilicity (A2 Only)6.5.3End of Topic Test - Amines
6.6

Polymers (A2 Only)

6.6.1Condensation Polymers (A2 Only)6.6.2Biodegradability (A2 Only)
6.7

Biological Organic (A2 Only)

6.7.1Amino Acids (A2 Only)6.7.2Proteins (A2 Only)6.7.3DNA (A2 Only)6.7.4Anti-Cancer Drugs (A2 Only)6.7.5End of Topic Test - Biological Organic
6.8

Organic Synthesis (A2 Only)

6.8.1Organic Synthesis (A2 Only)6.8.2Examples of Synthetic Routes (A2 Only)6.8.3End of Topic Test - Polymers & Organic Synthesis
6.9

NMR Spectroscopy (A2 Only)

6.9.1Understanding NMR (A2 Only)6.9.2Carbon-13 NMR (A2 Only)6.9.3Hydrogen-1 NMR (A2 Only)6.9.4Hydrogen-1 NMR 2 (A2 Only)6.9.5End of Topic Test - NMR
6.10

Chromatography (A2 Only)

6.10.1Overview of Chromatography (A2 Only)6.10.2Thin-Layer Chromatography (A2 Only)6.10.3Column Chromatography (A2 Only)6.10.4Gas Chromatography (A2 Only)6.10.5End of Topic Test - Chromatography
6.11

A-A* (AO3/4) - Organic 2

6.11.1A-A* (AO3/4) - Organic 2

Practice questions on Thin-Layer Chromatography (A2 Only)

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  1. 1
    When do you stop the TLC?Multiple choice
  2. 2
    Nature of phases in TLC:Fill in the list
  3. 3
    A component has a great affinity for the mobile phase. <br>Where will it be found on the TLC plate?Multiple choice
  4. 4
    What does TLC stand for?Multiple choice
  5. 5
    What are R<sub>f</sub> values dependent on?Multiple choice
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