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ANALYSING SUBSTANCES A guide for GCSE students

ANALYSING SUBSTANCES A guide for GCSE students. 2010 SPECIFICATIONS. KNOCKHARDY PUBLISHING. HOPTON. ANALYSING SUBSTANCES. INTRODUCTION

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ANALYSING SUBSTANCES A guide for GCSE students

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  1. ANALYSING SUBSTANCES A guide for GCSE students 2010 SPECIFICATIONS KNOCKHARDY PUBLISHING

  2. HOPTON ANALYSING SUBSTANCES INTRODUCTION This Powerpoint show is one of several produced to help students understand selected GCSE Chemistry topics. It is based on the requirements of the AQA specification but is suitable for other examination boards. Individual students may use the material at home for revision purposes and it can also prove useful for classroom teaching with an interactive white board. Accompanying notes on this, and the full range of AS and A2 Chemistry topics, are available from the KNOCKHARDY WEBSITE at... www.knockhardy.org.uk All diagrams, photographs and any animations in this Powerpoint are original and created by Jonathan Hopton. Permission must be obtained for their use in any work that is distributed for financial gain.

  3. HOPTON ANALYSING SUBSTANCES • CONTENTS • What is chromatography? • Paper chromatography • Gas liquid chromatography • Mass spectrometry • Questions

  4. HOPTON CHROMATOGRAPHY Chromatography is used to separate and analyse small amounts of mixtures

  5. HOPTON CHROMATOGRAPHY Chromatography is used to separate and analyse small amounts of mixtures Methods involve a stationary phase (stays where it is) and a mobile phase (moves) There are several forms of chromatography

  6. HOPTON CHROMATOGRAPHY Chromatography is used to separate and analyse small amounts of mixtures Methods involve a stationary phase (stays where it is) and a mobile phase (moves) There are several forms of chromatography TYPE STATIONARY PHASE MOBILE PHASE paper solid (filter paper) liquid thin layer (tlc) solid (silica) liquid column solid (silica) liquid gas liquid (glc) solid or liquid gas However, they all work in the same way

  7. HOPTON PAPER CHROMATOGRAPHY

  8. HOPTON PAPER CHROMATOGRAPHY Stationary phase chromatography paper Mobile phase suitable solvent (water, ethanol, organic solvent)

  9. HOPTON PAPER CHROMATOGRAPHY Stationary phase chromatography paper Mobile phase suitable solvent (water, ethanol, organic solvent) Separation As the solvent moves up the paper it dissolves the components and moves them up the paper. The more soluble a component is, the further it moves.

  10. HOPTON PAPER CHROMATOGRAPHY Stationary phase chromatography paper Mobile phase suitable solvent (water, ethanol, organic solvent) Separation As the solvent moves up the paper it dissolves the components and moves them up the paper. The more soluble a component is, the further it moves. Uses Separating the colours in Smarties® Separating the colours in, and identifying, inks

  11. HOPTON PAPER CHROMATOGRAPHY Stationary phase chromatography paper Mobile phase suitable solvent (water, ethanol, organic solvent) Separation As the solvent moves up the paper it dissolves the components and moves them up the paper. The more soluble a component is, the further it moves. Place small a spot of the mixture to be analysed (and any possible component for comparison purposes) on the paper. Dip the paper in the solvent.

  12. HOPTON PAPER CHROMATOGRAPHY Stationary phase chromatography paper Mobile phase suitable solvent (water, ethanol, organic solvent) Separation As the solvent moves up the paper it dissolves the components and moves them up the paper. The more soluble a component is, the further it moves. SOLVENT FRONT Place small a spot of the mixture to be analysed (and any possible component for comparison purposes) on the paper. Dip the paper in the solvent. Allow the solvent to rise up the paper. Each component dissolves in the solvent. Those which are more soluble travel further up the paper.

  13. HOPTON PAPER CHROMATOGRAPHY Stationary phase chromatography paper Mobile phase suitable solvent (water, ethanol, organic solvent) Separation As the solvent moves up the paper it dissolves the components and moves them up the paper. The more soluble a component is, the further it moves. SOLVENT FRONT Place small a spot of the mixture to be analysed (and any possible component for comparison purposes) on the paper. Dip the paper in the solvent. Allow the solvent to rise up the paper. Each component dissolves in the solvent. Those which are more soluble travel further up the paper. Finished chromatogram

  14. HOPTON PAPER CHROMATOGRAPHY Rf value Under similar conditions, a component should always travel at the same speed. Its identity can be found by comparing the distance it moves relative to the solvent. Rf = distance travelled by the component = Y distance travelled by the solvent X SOLVENT FRONT X Y

  15. HOPTON PAPER CHROMATOGRAPHY Rf value Under similar conditions, a component should always travel at the same speed. Its identity can be found by comparing the distance it moves relative to the solvent. Rf = distance travelled by the component = Y distance travelled by the solvent X Comparison can be a problem if… a) components have similar Rf values b) the unknown substance is new and there is no previous chemical to compare it with X Y

  16. HOPTON GAS LIQUID CHROMATOGRAPHY (GLC)

  17. HOPTON GAS LIQUID CHROMATOGRAPHY (GLC) Stationary phase liquid adsorbed onto a solid support material Mobile phase gas

  18. HOPTON GAS LIQUID CHROMATOGRAPHY (GLC) Stationary phase liquid adsorbed onto a solid support material Mobile phase gas Method • a very small amount of a sample is injected into the machine • the injector is contained in an oven • the sample boils and is carried along a thin column by an inert carrier gas

  19. HOPTON GAS LIQUID CHROMATOGRAPHY (GLC) Stationary phase liquid adsorbed onto a solid support material Mobile phase gas Method • a very small amount of a sample is injected into the machine • the injector is contained in an oven • the sample boils and is carried along a thin column by an inert carrier gas • the column contains a liquid stationary phase, adsorbed on an inert solid • the time taken to travel through the tube will depend on how much time is spent moving with the gas rather than being attached to the liquid.

  20. HOPTON GAS LIQUID CHROMATOGRAPHY (GLC) Retention time The time taken for a compound to travel through the column to the detector. It is measured from the time the sample is injected to the time its peak shows maximum height.

  21. HOPTON GAS LIQUID CHROMATOGRAPHY (GLC) Retention timeThe time taken for a compound to travel through the column to the detector. It is measured from the time the sample is injected to the time its peak shows maximum height. For a particular compound, the retention time depends on... boiling point high boiling point = long retention time

  22. HOPTON GAS LIQUID CHROMATOGRAPHY (GLC) Retention timeThe time taken for a compound to travel through the column to the detector. It is measured from the time the sample is injected to the time its peak shows maximum height. For a particular compound, the retention time depends on... boiling point high boiling point = long retention time solubility in the liquid phase greater solubility = long retention time

  23. HOPTON GAS LIQUID CHROMATOGRAPHY (GLC) Retention timeThe time taken for a compound to travel through the column to the detector. It is measured from the time the sample is injected to the time its peak shows maximum height. For a particular compound, the retention time depends on... boiling point high boiling point = long retention time solubility in the liquid phase greater solubility = long retention time ANIMATION

  24. HOPTON GAS LIQUID CHROMATOGRAPHY (GLC) Interpretation • each compound in the mixture will produce a peak • the areas under the peaks are proportional to the amount of a compound • retention times are used to identify compounds – they are found out by putting known compounds through the system under similar conditions The area under a peak is proportional to the amount present. Because each compound responds differently, the machine is calibrated beforehand to show the actual mount. Each component has a different retention time.

  25. HOPTON GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS)

  26. HOPTON GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS) Process When a peak is detected in gas chromatography, some of the component is sent to a mass spectrometer

  27. HOPTON GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS) Process When a peak is detected in gas chromatography, some of the component is sent to a mass spectrometer Mass spectrometers were first used to identify the presence of different isotopes. Today, they are mainly used to work out relative molecular (formula) mass and identify unknown molecules.

  28. HOPTON GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS) Process When a peak is detected in gas chromatography, some of the component is sent to a mass spectrometer

  29. HOPTON GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS) Process When a peak is detected in gas chromatography, some of the component is sent to a mass spectrometer A mass spectrometer has three main parts...

  30. HOPTON GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS) Process When a peak is detected in gas chromatography, some of the component is sent to a mass spectrometer A mass spectrometer has three main parts... ANALYSER DETECTOR IONISER

  31. HOPTON GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS) Process When a peak is detected in gas chromatography, some of the component is sent to a mass spectrometer A mass spectrometer has three main parts... Ioniser - the sample is bombarded with electrons and ionised - a positive molecular ion is formed - the molecular ion can break up into smaller ions ANALYSER DETECTOR IONISER PARTICLES MUST BE IONISED SO THEY CAN BE ACCELERATED AND DEFLECTED

  32. HOPTON GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS) Process When a peak is detected in gas chromatography, some of the component is sent to a mass spectrometer A mass spectrometer has three main parts... Ioniser- the sample is bombarded with electrons and ionised - a positive molecular ion is formed - the molecular ion can break up into smaller ions - positive ions are accelerated towards the analyser ANALYSER DETECTOR IONISER

  33. HOPTON GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS) Process When a peak is detected in gas chromatography, some of the component is sent to a mass spectrometer A mass spectrometer has three main parts... Ioniser - the sample is bombarded with electrons and ionised - a positive molecular ion is formed - the molecular ion can break up into smaller ions - positive ions are accelerated towards the analyser Analyser - positive ions separate according to mass/charge ratio - higher mass/charge ratio (heavier) = smaller deflection ANALYSER DETECTOR IONISER

  34. ANALYSER DETECTOR IONISER HOPTON GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS) Process When a peak is detected in gas chromatography, some of the component is sent to a mass spectrometer A mass spectrometer has three main parts... Ioniser - the sample is bombarded with electrons and ionised - a positive molecular ion is formed - the molecular ion can break up into smaller ions - positive ions are accelerated towards the analyser Analyser - positive ions separate according to mass/charge ratio - higher mass/charge ratio (heavier) = smaller deflection Detector - records the identity and abundance of each ion - compounds have a unique mass spectrum - the final peak (molecular ion) gives the molecular mass

  35. HOPTON GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS) Process When a peak is detected in gas chromatography, some of the component is sent to a mass spectrometer A mass spectrometer has three main parts... Ioniser - the sample is bombarded with electrons and ionised - a positive molecular ion is formed - the molecular ion can break up into smaller ions - positive ions are accelerated towards the analyser Analyser - positive ions separate according to mass/charge ratio - higher mass/charge ratio (heavier) = smaller deflection Detector - records the identity and abundance of each ion - compounds have a unique mass spectrum - the final peak (molecular ion) gives the molecular mass ANALYSER DETECTOR IONISER

  36. HOPTON MASS SPECTROMETRY - FRAGMENTATION Mass spectrometry is used to identify unknown or new compounds. The mass spectra of compounds are much more complicated than that of atoms because of fragmentation. When a molecule is ionised it forms a MOLECULAR ION which can undergo FRAGMENTATION or RE-ARRANGEMENT to produce particles of smaller mass. Only particles with a positive charge will be deflected and detected. The resulting spectrum has many peaks. The final peak shows the molecular ion and indicates the molecular mass. The rest of the spectrum provides information about the structure. IONISATION MOLECULAR ION FRAGMENTION RE-ARRANGEMENT FRAGMENTION

  37. HOPTON QUESTIONS

  38. HOPTON MASS SPECTRUM OF AN ORGANIC COMPOUND

  39. HOPTON MASS SPECTRUM OF AN ORGANIC COMPOUND Which signal is caused by the molecular ion?

  40. HOPTON MASS SPECTRUM OF AN ORGANIC COMPOUND The final signal in the spectrum is that of the molecular ion. Which signal is caused by the molecular ion?

  41. HOPTON MASS SPECTRUM OF AN ORGANIC COMPOUND What is the relative molecular (formula) mass of the compound?

  42. HOPTON MASS SPECTRUM OF AN ORGANIC COMPOUND 58 What is the relative molecular (formula) mass of the compound?

  43. HOPTON MASS SPECTRUM OF AN ORGANIC COMPOUND If the compound is a hydrocarbon, what is its molecular formula?

  44. HOPTON MASS SPECTRUM OF AN ORGANIC COMPOUND What is the relative molecular (formula) mass of the compound? C4H10

  45. ANALYSING SUBSTANCES THE END ©2011 JONATHAN HOPTON & KNOCKHARDY PUBLISHING

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