MODERN_ANALYTICAL_TECHNIQUES_SYLLABUS_plus_QUICK_and_DIRTY_(NXPowerLite) Opp

MODERN_ANALYTICAL_TECHNIQUES_SYLLABUS_plus_QUICK_and_DIRTY_(NXPowerLite) Opp

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1 Modern Analytical Techniques Compiled by MAH 2008 100’s of free ppt’s from www.pptpoint.com library
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2 IB OPTION A SL & HL
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3 A1 Analytical techniques
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4 A2 Principles of spectroscopy
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5 The Electromagnetic Spectrum:
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6
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7 Absorption spectra have parts ‘missing’. In the diagram below the troughs indicate energy absorbed by the molecules
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8 Observing with a hand held spectroscope gives you evidence for line emission spectra similar to the one shown below Here light is being emitted as the excited electrons drop down to lower ‘allowed’ energy levels.
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9
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10 a beam of infra red radiation is passed through the sample a similar beam is passed through the reference cell the frequency of radiation is varied bonds vibrating with a similar frequency absorb the radiation the amount of radiation absorbed by the sample is compared with the reference the results are collected, stored and plotted The Infra-red Spectrophotometer
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11 SYMMETRIC STRETCHING BENDING AND STRETCHING IN WATER MOLECULES
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12 ASYMMETRIC STRETCHING BENDING AND STRETCHING IN WATER MOLECULES
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13 BENDING AND STRETCHING IN WATER MOLECULES BENDING
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14 Vertical axis Absorbance the stronger the absorbance the larger the peak Horizontal axis Frequency wavenumber (waves per centimetre) / cm -1 Wavelength microns (m); 1 micron = 1000 nanometres INFRA RED SPECTRA - INTERPRETATION
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15 FINGERPRINT REGION organic molecules have a lot of C-C and C-H bonds within their structure spectra obtained will have peaks in the 1400 cm -1 to 800 cm -1 range this is referred to as the “fingerprint” region the pattern obtained is characteristic of a particular compound the frequency of any absorption is also affected by adjoining atoms or groups.
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16 IR SPECTRUM OF A CARBONYL COMPOUND carbonyl compounds show a sharp, strong absorption between 1700 and 1760 cm -1 this is due to the presence of the C=O bond
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17 IR SPECTRUM OF AN ALCOHOL alcohols show a broad absorption between 3200 and 3600 cm -1 this is due to the presence of the O-H bond
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18 WHAT IS IT! WHAT IS IT! O-H STRETCH C=O STRETCH O-H STRETCH C=O STRETCH AND ALCOHOL ALDEHYDE CARBOXYLIC ACID One can tell the difference between alcohols, aldehydes and carboxylic acids by comparison of their spectra.
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19 A4 Mass spectrometry
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20
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21 An outline of what happens in a mass spectrometer
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22 Peaks appear due to characteristic fragments (e.g. 29 due to C 2 H 5 + ) and  differences between two peaks also indicates the loss of certain units (e.g.  18 for H 2 O, 28 for CO and 44 for CO 2 ). Many of the fragments do not  show up themselves on the spectrum because they are not ions.
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23 FRAGMENTATION PATTERNS OF FUNCTIONAL GROUPS Interpretation of thousands of spectra has shown that many classes of organic compound show characteristic fragmentation patterns due to their functional groups. It is often possible to identify the type of compound from its spectrum by looking at the . .. • position of peaks
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