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The absorbance of UV and visible (UV–visible) radiations is measured using a UV–visible spectrophotometer. Deuterium lamps, which emit UV radiation, and tungsten lamps, which produce radiation in the visible region, are used as light sources in UV–visible spectrophotometers. A monochromator or prism is used for diffraction grating, i.e., to split the incoming radiation into different wavelengths. A system of slits is used to focus the desired wavelength on the sample cell.
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In a flame photometer, when a solution like potassium chloride is aspirated into the flame, the solvent evaporates, leaving behind dehydrated salt. This salt dissociates into free gaseous atoms in their ground state. Some of these atoms absorb energy from the flame, leading to their excitation. The excited atoms return to the ground state, emitting photons at characteristic wavelengths. Because only electronic transitions are involved, the resulting emission lines are very narrow. The intensity...
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Besides iodine, other oxidizing or reducing agents can serve as titrants in redox titrations. Common oxidizing titrants include KMnO4, cerium(IV), and K2Cr2O7. The choice of oxidizing titrants depends on factors like stability, cost, analyte strength, and reaction rate between the analyte and titrant. KMnO4 is a strong oxidizing titrant that reduces from Mn(VII) to Mn(II) in a highly acidic solution, simultaneously oxidizing the analyte to a higher oxidation state. In this case, KMnO4 acts as a...
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For AAS measurements, samples must be introduced as clear solutions, often requiring extensive preliminary treatment to dissolve materials like soils, animal tissues, and minerals. Common methods for sample preparation include treatment with hot mineral acids, wet ashing, combustion in closed containers, high-temperature ashing, or fusion with reagents.
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Weak acids and bases do not undergo dissociation completely, and titrations between these two are rarely studied. When such studies are performed, say, for the titration of a weak acid with a weak base, the titration curve plots the change in pH as a function of the volume of base added. Take the titration of acetic acid with ammonia, for instance. During the titration, these two species form ammonium acetate and water, but the pH change is slow and gradual.
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Predicting Precipitation
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Acidic Potassium Dichromate Solutions as Ultraviolet Absorbance Standards.

R W Burke1, R Mavrodineanu1

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Journal of Research of the National Bureau of Standards. Section A, Physics and Chemistry
|March 21, 2020
PubMed
Summary
This summary is machine-generated.

High-accuracy spectrophotometry of potassium dichromate solutions provides reliable absorbance measurements. These findings are crucial for calibrating spectrophotometers and ensuring accurate chemical analysis in various scientific fields.

Keywords:
Absorbance linearityaccuracyacidic potassium dichromate solutionscalibration of ultraviolet spectrophotometersliquid filterstransfer standardsultraviolet absorbance standards

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Area of Science:

  • Analytical Chemistry
  • Spectroscopy
  • Chemical Metrology

Background:

  • Accurate absorbance measurements are fundamental for quantitative chemical analysis.
  • Spectrophotometer calibration requires reliable standards and well-characterized absorbance values.
  • Understanding Beer's Law deviations is essential for precise spectrophotometric determinations.

Purpose of the Study:

  • To determine the absorbances of potassium dichromate solutions at specific ultraviolet wavelengths.
  • To evaluate the suitability of these wavelengths for spectrophotometer calibration and accuracy checks.
  • To assess the reproducibility and uncertainties in absorptivity values.

Main Methods:

  • Measurements were performed using a high-accuracy spectrophotometer at the National Bureau of Standards.
  • Absorbances of five potassium dichromate concentrations in perchloric acid were measured at eight UV wavelengths.
  • Wavelengths corresponding to spectral maxima/minima and predicted isosbestic points were selected.

Main Results:

  • Apparent absorptivities were reproducible to one part in a thousand.
  • Estimated uncertainties in absorptivity were ±0.7% at 0.1 absorbance and ±0.2% near 1 absorbance.
  • Wavelength 345 nm showed sufficient independence from concentration for linearity checks (0.2-1 A).

Conclusions:

  • Specific ultraviolet wavelengths are suitable for checking the absorbance accuracy of narrow bandpass spectrophotometers.
  • Potassium dichromate solutions, despite minor Beer's Law deviations, offer reliable standards for spectrophotometric calibration.
  • The study provides precise absorptivity data crucial for metrological applications in analytical chemistry.