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14 Cards in this Set
- Front
- Back
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How does matter interact with electromagnetic radiation to give color?
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- A sample absorbs electromagnetic radiation from source and the amount absorbed is related to the analyte in solution
- Cu ions are blue because they asborb the complementary color yellow from white light and transmit the remaining blue |
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What is electromagnetic radiation?
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Wave form produced by oscillating electric and magnetic field.
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What factors affect wavelength region of choice?
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1. availability of instruments
2. Is analyte colored or can be converted to colored derivative 3. Contains functional groups that absorb in the UV and IR regions 4. Other absorbing species are present in solution |
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What is the relation between wavelength and frequency?
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λ (lamda) = c/v
Wavelength = λ Frequency = v Speed of light = c = 3x 10^10 cm/s |
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How does matter absorb radiation?
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When polychromatic light (white) which contains whole spectrum of wavelengths in the visible region is passed thru an object, the object --> absorbs certain wavelengths, leaving unabsorbed wavelengths to be transmitted.
-These unabsorbed wavelengths (transmitted) will be seen as color. - Absorption of one color results in transmission of a complimentary color. |
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What are three ways in which photons are absorbed?
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1) rotation transition: rotate about covalent bonds
- occur in far-IR an microwave region 2) Vibration transition: molecule's covalent bond vibrate - mid and far IR region 3) Electronic transition: electron of molecules raise to higher electron energy. - visible and UV region. |
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What happens in energy loss when photons return to their ground state?
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the energy is emitted as:
- Fluorescence: relaxation transition in reverse emits a photon. - Raditionless: heat or vibration, rotation is passed to neighbors in media, very rapid in general. |
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What is Beer's law?
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the concentration of a substance is directly proportional to the amount of radiant energy absorbed (absorbance); also proportional to pathlength
A = abc a = absorptivity b = pathlength c = concentration of the substance |
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What to convert Absorbance and %Transmittance?
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A = 2.00 - log (%T)
%T = 10^(2.00 - A) |
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A sample in a 1.0 cm cell is determined with a soectrometer to transmit 80% light at certain wavelength. If the absorptivity of this substance at this wavelength is 2.0, what is the concentration of the substance?
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The %T is 80% so T = 0.80:
Log (1/T) = abc Log (1/0.80) = (2.0 cm-1g-1L)(1 cm)(c) Log 1.2 = (2.0g-1L)(c) c = (0.10/2.0) = 0.050 g/L OR A = abc A = 2 - log%T = 2 - log 80 = 0.1 c = A/ab = 0.1/(1cm x 2.0 g/L) = 0.050 g/L |
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A solution containing 1.00 mg ion in 100 mL, was observed to transmit 70% of the incident light compared to blank
What is the absorbance of this solution? |
A = 2 - log%T
%T = 70 A = 2 - log 70 = 0.155 |
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A solution containing 1.00 mg ion in 100 mL, was observed to transmit 70% of the incident light compared to blank
What is the fraction of light would be transmitted by a solution of iron 4 times as concentrated? |
A = 0.155
A = abc 0.155 = ab (0.0100 g/L) --> ab = 15.5 L/g A = 15.5 L/g (4 x 0.0100 g/L) = 0.620 Log 1/T = abc = A --> Log 1/T = 0.620 --> T = 0.240 |
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Describe the linear relationship between absorbance and concentration?
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As/Au = Cs/Cu
--> Cu = (Au/As) x Cs |
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What are conditions for Beer's law to be true?
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1. The solution is sufficiently dilute, less than 0.01 M
2. The radiation of one wavelength is used (monochromatic radiation) 3. The solvent absorbance is significant compared to the solute absorbance. 4. Stray light is minimized. 5. The sides of the cells are parallel. |
