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

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Presentation on theme: "ANALYSING SUBSTANCES A guide for GCSE students KNOCKHARDY PUBLISHING 2010 SPECIFICATIONS."— Presentation transcript:

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

2 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... 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. HOPTON

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

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

5 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 HOPTON

6 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 PHASEMOBILE PHASE papersolid (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 HOPTON

7 PAPER CHROMATOGRAPHY HOPTON

8 PAPER CHROMATOGRAPHY Stationary phasechromatography paper Mobile phasesuitable solvent (water, ethanol, organic solvent) HOPTON

9 PAPER CHROMATOGRAPHY Stationary phasechromatography paper Mobile phasesuitable solvent (water, ethanol, organic solvent) SeparationAs 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. HOPTON

10 PAPER CHROMATOGRAPHY Stationary phasechromatography paper Mobile phasesuitable solvent (water, ethanol, organic solvent) SeparationAs 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. UsesSeparating the colours in Smarties® Separating the colours in, and identifying, inks HOPTON

11 PAPER CHROMATOGRAPHY Stationary phasechromatography paper Mobile phasesuitable solvent (water, ethanol, organic solvent) SeparationAs 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. HOPTON

12 PAPER CHROMATOGRAPHY Stationary phasechromatography paper Mobile phasesuitable solvent (water, ethanol, organic solvent) SeparationAs 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. Allow the solvent to rise up the paper. Each component dissolves in the solvent. Those which are more soluble travel further up the paper. SOLVENT FRONT

13 HOPTON PAPER CHROMATOGRAPHY Stationary phasechromatography paper Mobile phasesuitable solvent (water, ethanol, organic solvent) SeparationAs 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. 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 SOLVENT FRONT

14 PAPER CHROMATOGRAPHY R f 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. R f = distance travelled by the component = Y distance travelled by the solvent X X Y SOLVENT FRONT HOPTON

15 PAPER CHROMATOGRAPHY R f 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. R f = distance travelled by the component = Y distance travelled by the solvent X Comparison can be a problem if… a) components have similar R f values b) the unknown substance is new and there is no previous chemical to compare it with X Y HOPTON

16 GAS LIQUID CHROMATOGRAPHY (GLC) HOPTON

17 GAS LIQUID CHROMATOGRAPHY (GLC) Stationary phaseliquid adsorbed onto a solid support material Mobile phasegas HOPTON

18 GAS LIQUID CHROMATOGRAPHY (GLC) Stationary phaseliquid adsorbed onto a solid support material Mobile phasegas 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 HOPTON

19 GAS LIQUID CHROMATOGRAPHY (GLC) Stationary phaseliquid adsorbed onto a solid support material Mobile phasegas 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. HOPTON

20 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. HOPTON

21 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 pointhigh boiling point = long retention time HOPTON

22 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 pointhigh boiling point = long retention time solubility in the liquid phasegreater solubility = long retention time HOPTON

23 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 pointhigh boiling point = long retention time solubility in the liquid phasegreater solubility = long retention time ANIMATION HOPTON

24 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. HOPTON

25 GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS) HOPTON

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

27 GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS) ProcessWhen 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. HOPTON

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

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

30 GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS) ProcessWhen 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 ANALYSER DETECTOR HOPTON

31 GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS) ProcessWhen 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 IONISER ANALYSER DETECTOR PARTICLES MUST BE IONISED SO THEY CAN BE ACCELERATED AND DEFLECTED

32 GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS) ProcessWhen 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 IONISER ANALYSER DETECTOR HOPTON

33 GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS) ProcessWhen 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 IONISER ANALYSER DETECTOR HOPTON

34 GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS) ProcessWhen 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 IONISER ANALYSER DETECTOR

35 HOPTON GAS CHROMATOGRAPHY – MASS SPECTROMETRY (GCMS) ProcessWhen 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 IONISER ANALYSER DETECTOR

36 IONISATION FRAGMENTION RE-ARRANGEMENT 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. MOLECULAR ION MASS SPECTROMETRY - FRAGMENTATION HOPTON

37 QUESTIONS

38 MASS SPECTRUM OF AN ORGANIC COMPOUND HOPTON

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

40 HOPTON MASS SPECTRUM OF AN ORGANIC COMPOUND Which signal is caused by the molecular ion? The final signal in the spectrum is that of 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 C 4 H 10 What is the relative molecular (formula) mass of the compound?

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


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