Uv-Vis Spectroscopy (1)

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VCE Chemistry

Unit 3 2013Chapter 7 UV-Visible Spectroscopy

Week commencing 18th FebMs Lennard


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Overview

Chapter 7 spectroscopy

The electromagnetic spectrum

UV-visible spectroscopy Theory for SAC Prac #1 Determination of the

P content of lawn food


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Chapter 7 - spectroscopy

We will study AA after we have completed

theory for the 1st SAC (EEI)

We will complete and IR, NMR after we have

completed Chapter 9 (organic chemistry)


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keywords

Electromagnetic spectrum UV (ultra violet) visible spectroscopy

Colorimetry (visible spectroscopy)

Calibration curve

Monochromator

Absorbance

Transmittance

Spectrum

photon


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wavelength


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Electromagnetic spectrum


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Electromagnetic spectrum

http://www.youtube.com/watch?v=kfS5Qn0w

n2o


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spectroscopy


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UV-Visible spectroscopy

Measures the light absorbed by substances as

their electrons jump to higher energy levels

The colour of a solution is the result of the

light transmitted by that solution after certain

components of visible light have been

absorbed through electron transitions

A coloured substance absorbs its complementary

colour eg. A solution appears yellow because the

blue and violet light has been absorbed and the

transmitted light is yellow


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UV-Visible spectroscopy

The position of a peak in a UV-vis spectrum shows

the energy of the light most strongly absorbed by

that substance

The amount of light absorbed is directly proportionalto the concentration of the compound

A calibration curve (generated from the

absorbance of samples of known concentration) is

used to determine the concentration of the

compound

UV-vis spectroscopy is used to determine

concentration of solutions of coloured compounds


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Beer - Lambert Law


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Visible light and complementary colours


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Visible light


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UV - vis


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UV- vis spectrophotometer


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faculty.sdmiramar.edu


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www.snypa.co.uk/OSR/UV/Resources/UV_spec.jpg


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http://www.youtube.com/watch?v

=0n-dbLzj_HM

You tube UV/Vis Spectroscopy


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Visible spectrum of the green pigment chlorophyll


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Using UV-Vis spectrum to choose the wavelength for analysis

choose a wavelength where the substance absorbs strongly

eg. 420nm or 660nm


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Calibration curves Enable unknown concentrations to be determined by

comparing with known standards (of concentration)

A series of standard solutions are tested using the

equipment under the same conditions

The response to these standards is measured andplotted to form a calibration curve (which is usually a

straight line)

The measurement of the unknown sample is plottedon the same curve and its position is used to find its

concentration

Calibration curves are used in AA and UV-Vis

spectroscopy


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Calibration curves


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Worked example 7.4 p. 87


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Worked example 7.4 p. 87


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Questions p. 88

Q6, 7, 9, 10, 11, 12


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2008 June Exam


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2008 June Exam


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2008 June Exam


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2008 June Exam


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2008 June Exam


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Uv-Vis Spectroscopy (1)