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45 Cards in this Set

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The spectronic 20 spectrophotomer is used for
to measure ability of a liquid sample to absorb light (in a visible region of electromagnetic spectrum) at a set wavelength
To obatin chemical or physical information you must have:
Signal generator
input transducer
signal modifier
output transducer
SISO for spect 20
s-tungsten lap
I-measuring phototube
S-analog amplifier
O-analog abs meter
Sensitivity limits
the abilit to separate signifcant data-containing signals from meaningless noise
define senisitivity
change in instrument response w/change in stimulus
fo absorption spectroscopy, sensitivity formula is
s=da/dc=
a is sample absorbance valu
c is saple concentration
sensitivity is affected by (3 things)
-physical & chemical properties of the analyte
-ddetector response
-composition of sample matrix
sensitivity is determined from...
the slope of the calibration curve:
absorbance vs concentration
At low concentrations, noise..
limits the lowest concentration of analyte that can be detected. aka it has hit the detection limit.
At high concentrations, noise..
fixes the precision of measurements.
for signal/noise signal enhancement, theres hardware that
-filters-blocks out unwanted
-integrators-increases coherent nonrandom sigover random noise
-modulators-shifts import freq away from noice
for signal/noice signal enhancement, software...
-boxcar averaging-lots of data points
-ensemble avearaging
-fourier transformations
define boxcar averaging
avg of a small series of data points to get one datapoint then use to get a curve.
mosteffectve w/fast signal
fourier transformation is used to
-convert time domain data f(t) into frequency domain data F(v)
-much faster than old frequ domain methods
FT's takes a single waveform and converts it into
a single line at frequ vo w/an amp a.
The FT conversion takes multicomponent waveforms that are generated by ____ & the sampling freq should by at least___
superposition of individual single frequ waves
&
2x that of the highest frequ component
define spectroscopy:
the measurement & interpretation of electromagnetic radiation (energy)absorbed/emitted when mcules of a sample move from 1 allowed energy state to another
electromagnetic radiation (light) has properties of:
-a microscopic particle having a discrete energy
-a wave extending over a broad area of space
light ineracts w/matter in only 3 fundamental ways:
reflectoin
transmission
absorption
=all 3 happen simutaneously
in the absorption process, the photon
is consumed & its energy is converted into an atomic or mcular process
in the absorption process its coverted into an atomic or mcular process meaning
-a nucleus spins in an altered manner
-a mcule vibrates differently
-an electron changes orbit
wavelength
λ-is measured as distance between 2 crests
period
T-is time elapsed between crests
T=1/V
frequency
V=# of waves that pass a fixed point in a given unit of time
amplitude
A- is max magnitued of the displacement
Intensity
I=proportional to the amplitude squared
A wave of electromagnetic radiation contains
electric field vectors
magnetic field vectors
plane polaraized light
electric field vectors
have periodic maxima perpendicular to direction of propagation
magnetic field vectors
orthogonal to electric field vectors
Plane polarized light
has its periodic field oscillations occuring in a set plane
The wavelength & frequency are related to energy E of a photon by Plank's constant,h, such that:
E=hv
In absorption or emission spectroscopy, the energy difference between the low energy state & high energy state is given by
bohr frequency condition:
{}E=hv
The only true characteristic of a particular wave of electromagnetic radiation is
frequency
the index of refraction depends on the
wavelength
frequency of electromagmetic radiation remains
constant, meaning photon energy is constant & waveletngth shorens as wave travels through matter
short wavelength(which means---energy) waves interact w/electrons----than long wavelength waves
high energy, more strongly
greater interaction of the waves gives a
larger n-index of refraction
monochromatic light
contains a single wavelength (or frequency) ex color, laser light
polychromatic light
contains spectral range of many wavelengths (ex white light)
constructive interference
in phase combination increases resulting amplitude
desturctive interference
out of phase combination decreaes resulting amp
the phase angle defines
period shift in periodic wave oscillations
define NMR
study of molcular sturcture by means of interaciton of radio frequency of e.r.w/a collection of nuclei immersed in a magnetic field,Ho
quantum mechanics- for a particle to absorb a photon of e.r., it must
first be in some uniform periodic motion
frequency of motion for e.r.must exactly match frequ of----& is true of all absorption spectroscopies
absorbed radiation
vmotion=vphoton