EXPERIMENT 17: SPECTROPHOTOMETRIC ANALYSIS Introduction Some chemical species ar

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EXPERIMENT 17: SPECTROPHOTOMETRIC ANALYSIS Introduction Some chemical species are capable of absorbing electromagnetic radiation EMR. You will recall from your lecture material that electromagnetic radiation has electrical and magnetic components which vary in a sinusoidal fashion. You should review the text and notes from your lecture material concerning electromagnetic radiation. EMR has a wave nature which consists of the variation in the electric or magnetic property either as a function of distance or as a function of time. The amount of energy possessed by electromagnetic radiation is directly proportional to the frequency v of the radiation as shown in Planck's equation [Equation (17-1)] where h is a proportionality constant termed the Planck constant. E- hu (17-1) The frequency of electromagnetic radiation is the number of repetitive units of the EMR (the number of waves) that pass a viewing point each second. Its unit is s which is also called Hertz Hz. It is related to the wavelength of the EMR by Equation (17-2). The wavelength is the length of one repetitive unit of the wave. In Equation (17-2) c is the velocity of EMR in a vacuum and n is the refractive index of the EMR in the medium through which the EMR is passing. The refractive index is the ratio of the velocity of EMR in a vacuum to its velocity in the medium. Consequently, c/n is the velocity of the EMR in the studied medium. (17-2) When EMR passes through a solution containing an absorbing chemical species, some of the energy associated with the multiple photons that contact the species are absorbed by the species A photon of radiation is the amount of EMR associated with the energy calculated by the Planck equation at a particular frequency. Essentially, absorption occurs when the energy of the absorbed EMR is used to perform some sort of work within the chemical species, thereby using the EMR to bring the chemical species to a higher energetic state. It is important to understand that not all chemical species absorb EMR at a particular frequency. Examples of changes that can occur when EMR is absorbed by a chemical species include raising an electron from a lower electron orbital to a higher electron orbital and causing a molecule to increase its rate of vibration or rotation. Electronic changes are particularly useful from the point of view of chemical analysis since EMR that is in the ultraviolet UV or visible Vis region of the spectrum is capable of making those changes. It is relatively easy to measure changes in the intensity of EMR in the UV/Vis region. Since the type of change that occurs in an absorbing species is dependent upon the frequency or wavelength of the EMR, it is important, while measuring the amount of absorbed EMR, to limit the wavelength or frequency of the EMR used for the measurement. EMR which contains a narrow wavelength or frequency band is monochromatic. Monochromatic radiation is used for chemical analysis. UV/Vis EMR absorption measurements are made as illustrated in Figure 17- 1. Normally a broadband EMR source is used. In order to convert the broad band

Explanation / Answer

Solved the first four parts of the problem Q1 as per chegg guidelines, please post multiple question to get the remaining answer

Q1)

a) T=0.209

A = -log(0.209) = 0.6798

b) %T = 17.3

A = -log(%T/100) = -log(17.3/100) = 0.761

c) %T = 54.8

A = -log(%T/100) = -log(54.8/100) = 0.2612

d) T = 0.615

A = -log(T) = -log(0.615) = 0.2111

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