《基础化学》英文教学课件:chapter-13.ppt
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1、Chapter 13.13-1.Absorption Spectrum 13-2.Quantitative calculations 13-3.Spectrometric instrumentation 13-4.Spectrometric error in measurementsIntroduction,particularly visible spectroscopy,is probably the most widely used analytical technique.It is based on the of the absorption of radiation(light)b
2、y molecules.Visible spectroscopy:380 nm 780 nm:200 nm 380 nmInfrared spectroscopy:780 nm 3105 nm1.Absorption SpectrumI.How does matter absorb radiation?When electromagnetic radiation(light)falls on a molecule,the molecule can be (from a ground state,)to a higher energy state(a excited state,),which
3、is called a.If the frequency of the radiation is (mu),it can raise the molecule to a state that differs in energy by an amount E,wherehE A molecule absorbs a photon(光子光子)by undergoing an energy transition exactly equal to the energy of the photon.The photon must have the right energy for this quanti
4、zed transition.1.Absorption SpectrumThere are three basic processes by which a molecule can absorb radiation:1.A molecule rotates about various axes,the energy of rotation being at definite energy levels,so the molecule may absorb radiation and be raised to a higher rotational energy level,in a.2.Th
5、e atoms or groups of atoms within a molecule vibrate relative to each other,and the energy of this vibration occurs at definite quantized levels.The molecule may then absorb a discrete amount of energy and be raised to a higher vibrational energy level,in a.1.Absorption SpectrumRotational transition
6、s can take place at very low energies(long wavelengths,that is,the microwave or far-infrared region),but vibrational transitions require higher energies in the near-infrared region,while.3.The electrons of a molecule may be raised to a higher electron energy,corresponding to an.KULeuvenAfdeling Foto
7、chemie en SpectroscopieProf.Dr.F.C.De SchryverSymmetricalstretchingAsymmetricalstretchingScissoring RockingWaggingTwisting Vibrations of methylene group(-CH2-)in a molecule for illustration:1.Absorption SpectrumAll the colors around us arise from the selective absorption and reflection of visible li
8、ght.When white light is passed through an object,the object will absorb certain of the wavelengths,leaving the unabsorbed wavelengths to be transmitted.These residual transmitted wavelengths will beseen as a color.This color is to the absorbed colors.In this color wheel,complementary colors are oppo
9、site each other.The numbers are approximate wavelength in nanometer.白光白光白光白光绿光绿光红光红光IntroductionI cannot pretend to be impartial about colors.I rejoice with the brilliant ones and am genuinely sorry for the poor browns.(30 November 1874-24 January 1965)KMnO4CuSO4KULeuvenAfdeling Fotochemie en Spectr
10、oscopieProf.Dr.F.C.De SchryverChemical structure of-carotene(-胡萝卜素).The eleven conjugated double bonds that form the chromophore(发色基团)of the molecule are highlighted in red.OHRetinol视黄醇视黄醇 -carotene-胡萝卜素胡萝卜素KULeuvenAfdeling Fotochemie en SpectroscopieProf.Dr.F.C.De SchryverGolden Rice 珀曲克斯 1.Absorpt
11、ion SpectrumII.Absorption spectrum:The extent that a matter or solution absorbs monochromatic light()。A plot of absorbance as a function of wavelength is called a an.The absorption spectra of chlorophyll a and chlorophyll b.1.Absorption Spectrum3003504004505005506006500.00.30.60.91.2 G2R1 G2R2 G2R3
12、G2R4AbsorbanceWavelength(nm)max:Qualitative analysisAbsorbance is proportional to the concentration:Quantitative analysis2.Quantitative CalculationsI.Transmittance and absorbanceItI。I0=Ia+It I0:Intensity of incident light()Ia:Intensity of absorbed light()It:Intensity of transmitted light()0tIIT 0tII
13、lglgTT1lgAThe fraction of radiant energy transmitted.2.Quantitative CalculationsII.Lambert-Beers LawThe amount of monochromatic light absorbed by a sample is described by the,commonly called.It says that the absorbance of a sample is proportional to the product of its concentration and the pathlengt
14、h(the thickness of the sample).bcAThis is not a beverage law!2.Quantitative CalculationsbcA:molar extinction coefficient(),unit:Lmol-1cm-1.It is dependent on the nature of the substance,the solvent,the wavelength of the incident light,and the temperature.c:concentration,unit:molL-1.b:pathlength,unit
15、:cm.Beers law is simple as abc.2.Quantitative CalculationsExample 13-1:A solution of Co(H2O)62+in a 1.00-cm cell was determined with a spectrometer to have an absorbance of 0.200 at 530nm.The extinction coefficient of Co(H2O)62+at this wavelength is known to be 1.00103 Lmol-1cm-1.Calculate the conce
16、ntration of Co(H2O)62+solution.bcAcm1.00cmmolL 101.000.200bAc-1-13Solution:-14Lmol102.002.Quantitative CalculationsExample 13-2:A solution containing 1.00 10-3 molL-1 Fe complex was observed to transmit 70.0%of the incident light using a 1.00-cm cell.(a)What is the absorbance of the solution at this
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