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INTRODUCTION
Department of Chemistry GENERAL CHEMISTRY 101 LABORATORY MANUAL An Inquiry Approach through an Environmental Awareness The following laboratories have been compiled and adapted by Alan Khuu, M.S. & Armando Rivera, Ph.D. CHEM 322 Quantitative Chemical Analysis Laboratory (Units: 2) Prerequisite: CHEM 321 with a grade of C or better (may be taken concurrently). Intended for Chemistry, Biochemistry, and Biology majors. Practical experience in performing accurate and precise measurements of chemical species in a variety of real-world samples using gravimetric, titrimetric, potentiometric, spectroscopic,.
Spectroscopy is the study of the interaction between matter and electromagnetic radiation. The types of electromagnetic radiation are often divided into the following broad categories (from short to long wavelengths): gamma radiation, X-ray radiation, ultraviolet radiation, visible radiation, infrared radiation, microwave radiation, and radio waves. Figure 1 illustrates the full electromagnetic spectrum.
Figure 1: The electromagnetic spectrum, with the visible spectrum highlighted
The visible spectrum of light is only one small sliver of the electromagnetic spectrum. It falls between approximately 400 nm to 700 nm, but our eyes distinguish the different wavelengths of light as different colors. The regions directly above and below this wavelength range are known as the infrared (IR) and ultraviolet (UV), respectively. The pigments in our eyes selectively absorb photons of the visible spectrum, but not those outside of it, because of their chemical makeup.
Department of Chemistry GENERAL CHEMISTRY 101 LABORATORY MANUAL An Inquiry Approach through an Environmental Awareness The following laboratories have been compiled and adapted by Alan Khuu, M.S. & Armando Rivera, Ph.D. Access study documents, get answers to your study questions, and connect with real tutors for CHEM 101 at Los Angeles Pierce College.
White light is a mixture of all visible wavelengths, which can be demonstrated by passing it through a prism or diffraction grating, which disperses the light into all of its component colors. When white light hits an object, some of the light may be reflected, some of it may be absorbed, and some of it may be transmitted (it passes through the object). Color arises from the selective absorption of photons of specific wavelengths. If the object is opaque, such as a wall, the reflected color is the complement of the color absorbed. If the object is transparent, such as a liquid, the transmitted color is the complement of the color absorbed. A spectrometer can separate the component colors coming either directly from an emission source or from the light transmitted through a sample. A top-down diagram of a spectrometer is shown in Figure 2.
Figure 2: The light path through a simple spectrometer
When the light from a simple emission source (like a single element) is viewed through a spectrometer, only specific lines of color are seen. Each of these lines corresponds to a unique electronic transition and the collection of lines is characteristic of the emission source. The emission spectrum for hydrogen is shown in Figure 3.
Figure 3: Production of the emission spectrum for hydrogen
A spectrophotometer is used to measure how much light is absorbed by a sample at varying wavelengths. In this instrument, a beam of monochromatic light is directed through a solution and the intensity of light transmitted (It) is compared to the intensity of the incident beam (Io), as shown in Figure 4. This fraction, sometimes expressed as a percentage, is termed the transmittance (T) of the sample at a particular wavelength:
[mathrm{T}=frac{mathrm{I}_{t}}{mathrm{I}_{o}}]
Figure 4: Simplified schematic of a spectrophotometer Telecharger les tudors saison 3 vf torrent.
Although it is sometimes useful to plot transmittance as a function of wavelength to get a transmittance spectrum, we will be focusing on absorbance (A), which is defined as:
[mathrm{A}=-log mathrm{T}=-log left(frac{I_{t}}{I_{o}}right)]
You can see from this equation that, as the transmittance diminishes, the absorption increases. Also, note that absorbance has no units.
In this experiment, you will use a spectrometer and a spectrophotometer to begin examining the different modes of light absorption and emission.
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