A study of the interaction of light (or other electromagnetic radiation) with matter is an important tool in quantitative analysis. Indeed, much of today's knowledge of chemical substances comes from their specific absorption or emission of light. Because all solutions of chemical compounds absorb light of specific wavelengths, spectrophotometry can be useful in identifying compounds. Furthermore, because the amount of light absorbed is proportional to the concentration of a compound, spectrophotometry is also useful in determining concentrations. .
The purpose of this experiment was to prepare an absorption spectrum of a starch-iodine solution by using the spectrophotometer. A spectrophotometer is an instrument designed to detect the amount of radiant light energy absorbed by a substance. An absorption spectrum is the plot of a sample's absorbance of light at various wavelengths. Before measuring the absorbance values for various wavelengths of light in the starch-iodine solution, I hypothesized that the absorbance data I was about to collect would produce a curve when plotted and graphed on a grid since, over an increasing range of wavelengths, the absorbance of a substance increases until it reaches a maximum point (lambda max) and then it decreases again. Next, I proceed to test my hypothesis. In order to get started, I turned the spectrophotometer on and let it warm up for 15 minutes. Meanwhile, I prepared two curvettes, which are standard matched tubes required in the use of a spectrophotometer. One of them was the experimental curvette, to which I added 4 ml of starch solution, 4 ml of water, and 0.1 ml of I2KI. The other one was "the blank", which consisted of all the components of the experimental solution except the 4 ml of starch. Then, I set the wavelength of the spectrophotometer to 440nm, the first wavelength listed in Table 1 (data sheet), and calibrated the spectrophotometer by placing the blank in the sample holder and setting the needle at 100 on the transmittance scale.