Electromagnetic Radiation and Interactions

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Questions and Answers

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?

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?

Red

Transparent

Black (correct)

White

What type of electromagnetic radiation has the highest energy and frequency?

Gamma Rays Signup and view all the answers

What is the relationship between wavenumber and wavelength?

Wavenumber is inversely proportional to wavelength Signup and view all the answers

What type of electromagnetic radiation is involved in nuclear magnetic resonance?

Radio waves Signup and view all the answers

What is the color of an object that reflects or transmits all wavelengths of visible light?

White Signup and view all the answers

What is the effect of UV and visible light on matter?

It causes outer electronic transition Signup and view all the answers

What type of radiation can a phototube detect?

UV or visible Signup and view all the answers

What is the purpose of a blank in UV-visible spectroscopy?

To set the absorbance to zero Signup and view all the answers

What is the process of amplifying electrons in a photomultiplier tube?

Electrons are amplified at each dynode Signup and view all the answers

What is the function of the beam splitter in a double beam spectrophotometer?

To split the beam into two Signup and view all the answers

What is the component that absorbs radiation in a phototube?

Cathode Signup and view all the answers

What is the purpose of the amplifier in a single beam spectrophotometer?

To amplify the signal Signup and view all the answers

What is the result of one photon hitting the photoemissive cathode in a photomultiplier tube?

106-107 electrons are emitted Signup and view all the answers

What is the voltage difference between the anode and cathode in a photomultiplier tube?

900V Signup and view all the answers

What is the main advantage of Double Beam Systems?

They correct for blank absorption Signup and view all the answers

What is the relationship between absorbance and transmittance?

Absorbance is inversely proportional to transmittance Signup and view all the answers

What is the purpose of the reference solution in a Double Beam System?

To provide a blank reading Signup and view all the answers

What is the advantage of Single Beam Systems?

They have high energy throughput Signup and view all the answers

What is the limitation of Single Beam Systems?

The sample and blank must be placed alternately in the light path Signup and view all the answers

What is the definition of transmittance?

The amount of light that passes through a sample Signup and view all the answers

Which solution has less transmitted light?

Solution a Signup and view all the answers

What is the purpose of Beer's Law?

To calculate the concentration of a solution Signup and view all the answers

What is the purpose of plotting a standard curve?

To establish a relationship between absorbance and concentration Signup and view all the answers

Why is it important for the chemical matrix of the standards and sample to be the same?

To ensure accurate results Signup and view all the answers

What is the comparison method used for?

To determine the concentration of an unknown sample Signup and view all the answers

What is the standard addition method used for?

To determine the concentration of a complex sample Signup and view all the answers

What is the assumption made when applying Beer's Law to mixtures?

That there is no interaction among the various species Signup and view all the answers

What is the total absorbance of a multicomponent system at a single wavelength?

The sum of the individual absorbances Signup and view all the answers

What is the purpose of adding different amounts of standard to the unknown sample in the standard addition method?

To determine the concentration of the unknown sample Signup and view all the answers

What is the advantage of using the standard addition method?

It is more accurate when the sample matrix is complex Signup and view all the answers

What is an example of a forensic application of chemistry?

Determining blood alcohol using the Breathalyzer test Signup and view all the answers

What is a characteristic of spectrophotometric titrations?

A sudden or sharp change in absorbance at the equivalence point Signup and view all the answers

What is the purpose of potassium permanganate in the analysis of hydrogen peroxide?

To act as an indicator Signup and view all the answers

How does the absorbance change as titrant is added in the analysis of hydrogen peroxide?

It changes suddenly at the equivalence point Signup and view all the answers

Why is it not necessary to have a data point at the equivalence point in spectrophotometric titrations?

Because the equivalence point can be located by extrapolation Signup and view all the answers

What is the role of the acidic solution in the analysis of hydrogen peroxide?

It helps to stabilize the reaction Signup and view all the answers

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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Description

This quiz covers the electromagnetic spectrum, interaction of electromagnetic radiation with matter, and related properties such as energy, frequency, wavenumber, and wavelength.