The rate of a first-order reaction is followed by spectroscopy, monitoring the absorbance of a colored reactant at 520 nm. The reaction occurs in a 1.00-cm sample cell, and the only colored species in the reaction has an extinction coefficient of 5.60 * 103 M-1 cm-1 at 520 nm. (a) Calculate the initial concentration of the colored reactant if the absorbance is 0.605 at the beginning of the reaction.

Video transcript

Hello everyone today. We are being asked to solve the following problem. It says spectroscopy uses visible light to determine the absorbent of a compound. At 275 nm. A compound has an extinction coefficient of 8.4 times 10 to the third molar times cm in verse. We are then asked to determine the malaria T. Of the compound. If it has an absorbent of 0.7 in a one centimeter sample que vete. So the first thing we want to do is we want to recall beer's law, which is the absorbent times the path and length times our extinction coefficient times our C. The next thing you wanna do is we want to take note of our different variables that we have. So we see in the question stem that we have a which is .7. We have our b. Which is our one cm and we have our extinction coefficient here, which is The 8.4 times 10 to the 3rd. And so we need to find C. We can do that by rearranging this equation to get C. Is equal to the absorbent over the extinction coefficient times the path, light and length, Plugging in our variables for a. We have 0.7 we have 8.4 times 10 to the third here, we're going to multiply that by one And we're gonna get a final answer of 8.33 times 10 to the -5 molar for our concentration. I hope this helped. And until next time