10 Questions
The Hehner tube is designed to add the solution to the more concentrated solution until the color of the sample and the standard solution match.
False
The Duboscq colorimeter is used in the visual method for determination of colored samples.
True
Spectrophotometer can measure both the intensity of light absorbed and transmitted through a sample.
True
The Beer-Lambert law is not relevant to UV/Visible Spectroscopy.
False
One of the advantages of using a spectrophotometer is that it cannot provide quantitative data about a sample.
False
One of the components of a spectrophotometer is a monochromator, used to isolate specific wavelengths of light.
True
A Hehner tube is primarily used to mix solutions in UV/Visible Spectroscopy.
False
The Variable Depth or Balancing method in UV/Visible Spectroscopy does not involve comparing light intensities of sample and standard solutions.
False
UV/Visible Spectroscopy is only applicable to colored samples, not colorless ones.
False
In Instrumental methods of UV/Visible Spectroscopy, light absorption by a sample is measured electrically.
True
Study Notes
Spectrophotometer vs Colorimeter
- Spectrophotometers have a wider wavelength range and a more stable light source than colorimeters.
Components of a Spectrophotometer
- Light source: emits wavelengths in the range of interest
- Dispersing system (Monochromator): selects the wavelength of interest
- Sample compartment (Cuvette): holds the sample
- Detector: converts radiation energy to a measurable signal
- Recorder (readout unit): converts the signal to data
Light Source
- Requirements: intense, continuous, constant, and uniform radiation
- Types: Hydrogen or Deuterium lamp (UV region), Tungsten lamp (visible region)
Monochromators
- Function: selects monochromatic radiation from polychromatic radiation
- Components: entrance slit, dispersing element, exit slit
- Types of dispersing elements: filter, prism, grating
Colorimetry
- Defined: method for quantitative analysis by measuring absorption in the visible region (400-750 nm)
- Requirements for substances to be measured: colored or able to form colored solution with a reagent (chromogen)
Characteristics of Chromogen
- Should be colorless
- Selective (reacts with analyte only)
- Reacts with the analyte quantitatively (stoichiometrically)
- Rapid reaction and color development
- Produces single colored product of specified λmax
Characteristics of the Color
- Intensive
- Stable for at least one hour
- Obeys Beer-Lambert's law
- Produces a clear colored solution
UV/Vis Methods in Quantitative Analysis
- Visual methods: used for determination of colored samples
- Instrumental methods: used for determination of colored and colorless samples
Visual Methods
- Standard series method: compares test solution with a series of standards
- Variable depth or balancing method: uses light intensity to match sample and standard solutions
Equipments Used in Variable Depth Method
- Hehner tube: withdraws solution until the color of the sample and standard solution are matched
- Duboscq colorimeter: measures the intensity of light absorbed by a sample
Test your knowledge on the components and advantages of spectrophotometers compared to colorimeters. Learn about the functions of light sources, monochromators, cuvettes, and detectors in UV/visible spectroscopy instruments.
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