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Questions and Answers
What happens to the wavelength as the energy of electromagnetic radiation increases?
What happens to the wavelength as the energy of electromagnetic radiation increases?
- It remains the same
- It becomes zero
- It decreases (correct)
- It increases
What type of transition is affected by X-rays?
What type of transition is affected by X-rays?
- Nuclear magnetic resonance
- Outer electronic transition
- Molecular vibration
- Inner electronic transition (correct)
What is the color of an object that absorbs all wavelengths of visible light?
What is the color of an object that absorbs all wavelengths of visible light?
- Red
- Transparent
- Black (correct)
- White
What type of electromagnetic radiation has the highest energy and frequency?
What type of electromagnetic radiation has the highest energy and frequency?
What is the relationship between wavenumber and wavelength?
What is the relationship between wavenumber and wavelength?
What type of electromagnetic radiation is involved in nuclear magnetic resonance?
What type of electromagnetic radiation is involved in nuclear magnetic resonance?
What is the color of an object that reflects or transmits all wavelengths of visible light?
What is the color of an object that reflects or transmits all wavelengths of visible light?
What is the effect of UV and visible light on matter?
What is the effect of UV and visible light on matter?
What type of radiation can a phototube detect?
What type of radiation can a phototube detect?
What is the purpose of a blank in UV-visible spectroscopy?
What is the purpose of a blank in UV-visible spectroscopy?
What is the process of amplifying electrons in a photomultiplier tube?
What is the process of amplifying electrons in a photomultiplier tube?
What is the function of the beam splitter in a double beam spectrophotometer?
What is the function of the beam splitter in a double beam spectrophotometer?
What is the component that absorbs radiation in a phototube?
What is the component that absorbs radiation in a phototube?
What is the purpose of the amplifier in a single beam spectrophotometer?
What is the purpose of the amplifier in a single beam spectrophotometer?
What is the result of one photon hitting the photoemissive cathode in a photomultiplier tube?
What is the result of one photon hitting the photoemissive cathode in a photomultiplier tube?
What is the voltage difference between the anode and cathode in a photomultiplier tube?
What is the voltage difference between the anode and cathode in a photomultiplier tube?
What is the main advantage of Double Beam Systems?
What is the main advantage of Double Beam Systems?
What is the relationship between absorbance and transmittance?
What is the relationship between absorbance and transmittance?
What is the purpose of the reference solution in a Double Beam System?
What is the purpose of the reference solution in a Double Beam System?
What is the advantage of Single Beam Systems?
What is the advantage of Single Beam Systems?
What is the limitation of Single Beam Systems?
What is the limitation of Single Beam Systems?
What is the definition of transmittance?
What is the definition of transmittance?
Which solution has less transmitted light?
Which solution has less transmitted light?
What is the purpose of Beer's Law?
What is the purpose of Beer's Law?
What is the purpose of plotting a standard curve?
What is the purpose of plotting a standard curve?
Why is it important for the chemical matrix of the standards and sample to be the same?
Why is it important for the chemical matrix of the standards and sample to be the same?
What is the comparison method used for?
What is the comparison method used for?
What is the standard addition method used for?
What is the standard addition method used for?
What is the assumption made when applying Beer's Law to mixtures?
What is the assumption made when applying Beer's Law to mixtures?
What is the total absorbance of a multicomponent system at a single wavelength?
What is the total absorbance of a multicomponent system at a single wavelength?
What is the purpose of adding different amounts of standard to the unknown sample in the standard addition method?
What is the purpose of adding different amounts of standard to the unknown sample in the standard addition method?
What is the advantage of using the standard addition method?
What is the advantage of using the standard addition method?
What is an example of a forensic application of chemistry?
What is an example of a forensic application of chemistry?
What is a characteristic of spectrophotometric titrations?
What is a characteristic of spectrophotometric titrations?
What is the purpose of potassium permanganate in the analysis of hydrogen peroxide?
What is the purpose of potassium permanganate in the analysis of hydrogen peroxide?
How does the absorbance change as titrant is added in the analysis of hydrogen peroxide?
How does the absorbance change as titrant is added in the analysis of hydrogen peroxide?
Why is it not necessary to have a data point at the equivalence point in spectrophotometric titrations?
Why is it not necessary to have a data point at the equivalence point in spectrophotometric titrations?
What is the role of the acidic solution in the analysis of hydrogen peroxide?
What is the role of the acidic solution in the analysis of hydrogen peroxide?
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Study Notes
Electromagnetic Spectrum
- Electromagnetic radiation: energy, frequency, wavenumber, and wavelength are related
- Gamma rays: affect and excite atomic nuclei, high energy, high frequency, short wavelength
- X-rays: effect inner electronic transitions, high energy, high frequency, short wavelength
- UV and visible light: effect outer electronic transitions
- IR: molecular vibration
- Microwave: molecular rotation, electronic spin resonance
- Radio waves: low energy, low frequency, long wavelength
Interaction of EMR with Matter
- Absorption of light: if a sample absorbs all wavelengths in the visible region, it will appear black; if it absorbs none, it will appear white
- Colors of light: the color of an object we see is due to the wavelengths transmitted or reflected
Photodetectors
- Phototubes and photomultipliers: contain a photosensitive surface that absorbs radiation, producing an electrical current proportional to the number of photons
- Phototube: emits electrons from a negatively charged cathode when struck by visible or UV radiation
- Photomultiplier tube: amplifies electrons through a series of dynodes, producing a large current
UV-Visible Instruments
- Single beam instruments: less expensive, high energy throughput, but sample and blank must be placed alternately in the light path
- Double beam instruments: more accurate, automatically corrects for blank absorption, but more expensive
Relationship between Absorbance and Transmittance
- Transmittance (T): the amount of light that passes through a sample
- Absorbance (A): related to transmittance by A = -log(T)
Beer's Law
- Relates absorbance to concentration and path length
- Can be used to determine the concentration of an unknown sample
- Methods for using Beer's Law:
- Calibration curve: measure absorbance of a series of standard solutions and plot a standard curve
- Comparison method: use a single standard solution
- Standard addition method: add different amounts of standard to the unknown sample
- Applying Beer's Law to mixtures: the total absorbance is the sum of the individual absorbances
Applications of Molecular Absorption Spectrometry
- Quantitative analysis: determining the concentration of a substance
- Spectrophotometric titrations: following a reaction if at least one substance is colored
- Forensic chemistry: determining blood alcohol levels using a Breathalyzer test
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