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Unformatted text preview: Lab Report Devon Corcoran Chem. II Lab Dr. Ward Spectrophotometric Analysis of Colored Solutions Introduction The observed color of a liquid is the result of the frequencies of light that pass through the liquid. The rest of the light frequencies are absorbed, and each of these colors can be represented by a specific wavelength ( ) in nanometers. λ Color Red Orange Yellow Green Blue Violet λ 670 nm 620 nm 590 nm 550 nm 490 nm 430 nm Spectrophotometers are instruments that allow us to select a wavelength of light, pass it through a sample, and measure the intensity of the light that passed through the sample, allowing us to gauge the sample’s absorption of that frequency of light. The amount of light that passes through the sample will be measured as % T, or percent transmittance. It is measured as a percentage because the spectrophotometer measures the intensity of the light before it reaches the sample and after it has passed through the sample, and electronically calculates a value that is the ratio of transmitted light to the initial intensity. The alternative to measuring a %T is to measure an absorbance of the sample. The absorbance of the sample is calculated by the expression ( 29 T Log A % 2- = . The mathematical relationship between the %T and the absorption is an inverse function. When %T increases, absorption decreases. This makes sense, because you would expect more light to be absorbed with a lower percent transmittance. The amount of light absorbed is a function of the color of light used. In this experiment, we are looking for the color with the highest rate of absorbency ( λ max ). Using the spectrophotometer, we can graph wavelength versus absorbance and obtain the spectra of the sample. Theoretically, every substance has a different λ max and a unique spectra graph overall. The other two factors that affect absorption are the thickness and unique spectra graph overall....
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