 Part of the next exercise in your lab will involve you determining the absorption of different concentrations of your dye at a given wavelength. And that given wavelength is actually the maximum wavelength that you calculated from part one. So that is 630 nanometers according to what I got. And what you will do is you're given a concentration of your dye and you're going to make a series of dilutions and then when you determine the absorbance and the percentage transmission, you can actually come up with your calibration curve, which is your concentration on your x-axis plotted against your absorbance on your y-axis. And the concentrations, when I did my calculations, the concentrations were actually in molar concentrations so mole per liter and they are raised to 10 to the minus 6, so it's a very low concentration of dyes that we're working with. So in order for us to accurately or easily represent it, I should say on a graph, you can represent your concentrations in whole numbers, but just know that when you're dealing with a concentration, you're actually multiplying what you get by 10 to the minus 6. So that eliminates the worry of having to represent these small decimal numbers on your graph. And of course your absorbance can be plotted as is. And then the curve that you get gives you the relationship between your absorbance and your concentration. So as your concentration increases, your absorbance increases. So because of this, if you have your curve, and this can be also termed as a standard curve because you know the concentrations corresponding to the absorbance of these set samples. So you can determine the concentration of an unknown, which is mouthwash in this case that I use because mouthwash has brilliant blue dye in it. So you can measure the absorbance of your mouthwash using the spectral photometer and then you can plot. So you go on your y-axis and you determine where your absorbance is. So I had gotten 0.987 as my absorbance for the mouthwash. So I find, locate this on the graph and I extrapolate, I'm going to use the absorbance to extrapolate and get my corresponding concentration at that absorbance. So all you do here is you draw lines from your value, your absorbance value to meet the curve and then you draw the line from the curve, these dotted lines from the curve to meet your x-axis, which is going to give you the concentration. So therefore, reading from our graph, the concentration of the mouthwash is 7.6 times 10 to the minus 6 moles per liter or molar. Another thing that you were asked to do was to determine the molar absorptivity of the dye, the brilliant blue dye in my case. So basically the molar absorptivity is how strongly a dye absorbs light at a particular wavelength. The wavelength we are looking at, 630 nanometers, and the absorptivity is actually a measured value. So there's an equation that we can use to determine our molar absorptivity. The equation is called the Beer's equation. So it says A is equal to E epsilon times B times C. Epsilon represents our molar absorptivity. B is actually the path length of the light that we're measuring. Concentration is in most per liter or molarity. And the path length is normally fixed, it's a fixed value at 1 centimeters. And this only changes if you're told that it's not 1 centimeter. So always use 1 centimeter as the path length in your calculations. So you can rearrange the formula so that you're solving for the molar absorptivity. So therefore, the molar absorptivity would be equal to the absorbance over the path length times the concentration. So you know your absorbance value, which is 0.987. You know your concentration, which we determined from our curve. And then we multiply. So we divide our absorbance value by our path length times the concentration. And it should get a number looking like this, 1.3 times 10 to the fifth. And this is written in liters per mol centimeters. So this is what we have calculated, the molar absorptivity of the brilliant blue dye. So these are, this is just an example of what you'll be doing in the lab. And by following, by looking at these steps, you'll be able to determine what you need to do for the spectrophotometer lab.