Quantitative Chemical Analysis: CH 18 Fundamentals of Spectrophotometry Flashcards


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Chapter Outline • Section 181 Properties of Light • Section 182 Absorption of Light • Section 183 Measuring Absorbance • Section 184 Beer's Law in Chemical Analysis • Section 185 Spectrophotometric Titrations • Section 186 What Happens When a Molecule Absorbs Light?
updated 3 weeks ago by c_mylinh
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1

Spectroscopy

the theoretical approach to the science of studying the interaction between matter and radiated energy

2

Spectrometry

the practical application of spectroscopy

3

Spectrometry uses instruments called

spectrometers

4

Spectrophotometry

the method used to measure how much achemical substance absorbs light as a beam of light passes through asample solution

5

Spectrophotometers

the instruments used to quantitatively measure the reflection or transmission properties of a material as a function of wavelength (a spectrum)

6

Spectrum

the reflection or transmission properties of a material as a function of wavelength

7

Light behaves as: (2)

a WAVE and a PARTICLE

8

Light as a WAVE

- has a wavelength and frequency

- exhibits the wave phenomena of interference, diffraction, and reflection.

- Wave properties govern light behavior such as interference and diffraction

9

Wave properties govern light behavior such as

interference and diffraction

10

Light as a PARTICLE (a photon)

- carries a discrete energy that can be absorbed or emitted by a molecule.

- The interaction of light with chemicals is described using the particle nature of light—the photon and its energy

11

Light waves consist of

card image

perpendicular, oscillating electric and magnetic fields

12

Wavelength, λ

the distance between wave crests

13

Wavelength units

m, µm, nm

14

Wavenumber (v)

card image

a measure of spatial frequency

(v = 1/λ)

15

Frequency, ν

  • the number of oscillations per second of the wave
  • Frequency has
    units of hertz (s-1).
  • 1 Hz = 1 oscillation per second

16

Speed of light, c, formula

  • The product of wavelength times frequency
  • νλ = c
  • In a vacuum, all light travels at the same speed.
    c = 2.998 × 108 m/s

17

Light has a duality of

Wave-Particle

18

What is the smallest amount of light that can be generated by a light source?

A photon is the smallest amount of light that can be generated by a light source.
A photon is a particle of light.

19

The energy of a photon can be calculated from its

frequency

20

Photon energy formula

Ephoton = hν

where

h = Planck’s constant = 6.626 × 10-34 J∙s
ν = the frequency of the photon in units of hertz, s-1
E = the energy of the photon in units of joules, J

21

Constants

c = 2.998 × 108 m/s (the speed of light in a vacuum)
h = 6.626 × 10-34 J∙s (Planck’s constant)

22

Equations

v = 1/λ (conversion equation between wavelength and wavenumbers)

λν = c (equation for speed of light in a vacuum)

Ephoton = hν (equation for energy of a photon of light)

E = hν = hc/λ = hcv

23

Our eyes only see a fraction of the light in the universe. T/F?

True

24

Spectrophotometry

Any technique that uses light to measure chemical concentrations

25

Absorption Spectrophotometry

Any technique that uses the absorption of light to measure chemical
concentrations