CHEM 101 1nd Edition Lecture 18Outline of Last Lecture I. pH: Potential HydrogenII. pH and [H+]III. Determining the Concentration of an Unknown Acid or Base Solution via TitrationOutline of Current Lecture I. SpectroscopyCurrent LectureI. Spectroscopy a. Terms Describing Absorption (Beer's Law)i. Consider a beam of light with an (initial) radiant intensityii. The light passes through a solution of concentration (c)iii. The thickness of the solution is "b" cmiv. The intensity of the light after passage through the solution (where absorption occurs) is Pb. Definitionsi. Transmittance (T) = P/P0 (units = %)ii. Absorbance (A) = (units = none)1. A = log (P0/P)2. A = log (1/T) = -log (T)3. A = abc or (εbc) <-- Beer's Lawa. a = absorptivity (L/g cm)b. b = path length (cm)c. c = concentration (g/L)d. ε = molar absorptivity (L/mol cm)i. Used when concentration is in molar unitsiii. Beer's law is a relation between absorbance and concentration which is a straight line that passes through the origin in a constant path length, b, and at certain wave length, l These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.1.2. Slope = eb3. A=ebciv. Transmittance decreases exponentially as concentration increases. 1.2. T=10-A =10- ebcc. Beer's Law i. A = εbcii. Wavelength Dependence, l1. A blue solution absorbs red light.a. Allows blue light to go through, absorbs other wavelengths. 2. A red solution can not absorb the red light but it can absorb light that is complimentary to rediii. Path length Dependence, b1. Let us assume that we doubled the path length of light through the absorbing medium.a. The absorbance would double from the original measurement.b. The same would happen if we tripled the length, the absorbance would trip from the original. iv. Concentration Dependence, c1. If the concentration of the solution were to increase, less light would pass through.2. This would cause the absorbance to increase. v. ε1. Molar Absorptivity is a constant2. Particular to the substance.3. Particular for a
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