 So this is how your spectrophotometer is going to look, the one that you probably will be using in the lab. So I'm going to show you some important features of this spectrophotometer. And there are certain knobs here that you need to be familiar with. For example, this is the home screen, where it will bring you to this interface where you have a series of suggestions that you can select. So we're going to use the spec 200 modern interface option. So our enter button is actually this circular button in the center of the arrow buttons. So we press that. And if you notice, it gives us this display. And we are going to be measuring in the live display mode. And we can either measure in absorbance or in percentage transmittance. So if you notice in your lab write up, there is a calculation to calculate the percentage transmittance and the absorbance. But you won't have to use a calculator to do that in this case. You actually will get a reading of your absorbance. If you want to change the measurement from absorbance to transmittance, all you need to do is suppress the right arrow. And if you notice the sign percent T comes up. So whatever you measure will be the percentage transmittance. And next you see here the measurement. So right now it's telling you that you're going to be measuring your absorbance at 675 nanometers, which is your wavelength. So your wavelength is depicted in nanometers. Now if you want to change the wavelength at which you're reading your absorbance, you can use this dial here. If you notice lambda is written on the dial. So first you have to go to the measurement mode. Now you can do one of two things to change the wavelength. If you want to change it by an increment of 1 nanometer, you can go either left. So if you notice it's now 676, 677. If you want to bring it down, you could go to the left arrow, which gets you to 676, back to 675. If you want to change it in increments of 10, you can use this dial over here to the left, mark lambda. So it will go up to from 6, what was it? 675, it can go if you turn the dial clockwise to 685. If you want it down anticlockwise, it will go to 665. You can also use this dial to do fine adjustment. If you press down on the knob and you turn it, it will go in increments of 1 nanometers, either up or down. So that's how you would adjust your wavelength. Now if you want to actually do your measurement, you have to press your down arrow until it gets the go letters. And if you notice, whenever your words are highlighted in green, it means that that's the highlighted thing that will happen if you press Enter. So if you press Enter, it will go and then start measurement. So nothing is in our sample holder yet. So I'm just showing you where you're going to actually put your samples. Now if you notice here inside of the spectrophotometer, there is a light source, which is right here. So this light source is actually sending light from the monochromometer. And this is going to hit your sample, which can either be in the place where a cuvette is, or it could be in the place where you put your test tube. So I have here a cuvette. I can put the cuvette in here if my sample. Let's say this was my sample. I could put it in. And you'll notice it fits very snugly into the cuvette holder. And then I could press Enter. No, I can actually then determine the absorbance. So it's telling me right now that the absorbance is sorry, it's actually telling me the percentage transmittance. It's in 83.3%. So if you notice what happens here, you notice the numbers are changing. It's changing every five seconds because it's reading the percentage transmittance every five seconds. So what I would advise you to do is if you're using a cuvette, you put your sample in. You close it down. You press to read. The first reading it gets, you press again. When you press the Enter button here, it will freeze the display so you can write down the value that you have. And then you can go now back to your home screen if you want to determine the absorbance value. It's going to take you directly back to the home screen. So you have to press that you want to go into the spec 200 modern interface. You go scroll down to the absorbance section. It's already in absorbance. You can just continue. Press Enter to go. And then it's going to read your absorbance. And then you click to freeze the display. Click Enter to freeze the display. Then you record your absorbance value. And then you can move on to doing your next measurement. So that's if you are using a cuvette. So for part one, you are required to actually determine the percentage transmittance and your absorbance value of a given dilution of your blue dye. And you're going to be doing that at different wavelengths. So you're going to start from a wavelength of 250 nanometers to 650 nanometers. So in order to do this, since you're measuring dye, the quantity of dye or the absorbance of the dye in the sample, the first thing you need to do is to blanket with whatever the dye is dissolved in, which is water in this case. So you want to make sure that the water is set to 100% transmittance. So that means the water is not going to be anything absorbed by the water is not going to be recorded. The only thing that will be recorded is what is absorbed by your dye. So you have to make sure you are blank so that you get rid of any residual absorbance by the water and only measure the absorbance of your dye. So since I'm using a test tube here, I'm going to show you where to put your blank, which contains your water. You're going to put it in the part which is marked your test tube. And if you notice in here, there's this button that can adjust the holder for your test tube. So if you're using a bigger test tube, you can actually make this area bigger by pushing on this lever. And it will go further down. And if you notice, it's big. So this would be for a bigger test tube. But I want it to fit my test tube strongly so I push it back up. And I tighten the screw in a clockwise motion to keep it stable. So my blank is here, and I'm ready to blank. So this is what I do if I need to blank my sample. So I go back to the home screen, I hit the Enter button, and then I go to transmittance. I select transmittance because I want to make sure that I have 100% transmittance for my blank. So I select that, and let's say I'm measuring at 675. That's my wavelength. So I go to the Go button, and then I click Enter. When I click Enter, this 0.00 button is actually going to allow me to auto-zero. It's called auto-zero in the water so that it will be registered as 100% transmittance, zero absorbance. So I press that, and here, if you notice, it's saying perform in auto-zero. So you leave it alone. And then it will record your transmittance as 100% or close to that. So it's recorded at 100% if you notice here. So I froze the screen so that you can see it. Now we can go back to our home screen to make sure that the absorbance is little or nothing. So since it's already selected for absorbance, we go to the Go button. And if you notice, our absorbance is 0.006, which is basically nothing. So you know that you have no absorbance and maximum transmittance. Another thing I want you to pay attention to on the screen of your spec 200, what is nice about this instrument is that it shows where on the spectrum you're actually absorbing your substance at. So here it's showing you that you're at 675. So it's in the red portion of your white light spectrum. So you can actually determine that. So now that I've done my absorbance, I can switch my blank with my sample. So I've done my auto-zero. So I can switch my blank with my sample. And then I can measure the absorbance of my sample. So I'm going to go back to the home screen and select. First of all, I'm going to select, well, I can do the absorbance first. So first, let me change the wavelength because you're going to start measuring from 350 nanometers. So I'm going to change my wavelength. So it's going down. I go anti-clockwise so I can go to 350. And since I am, and if you notice, it went down and stopped at 340 because that's the lowest wavelength that you can measure using the spectrophotometer. And the highest wavelength you can measure is 1,000. So I actually have to blank again because I changed my wavelength before I was at 675. So now I need to blank at 350. So I am going to hit go. So what I'll do, I go back to transmittance since I'm blanking. And then I'm going to hit go. And then I'm going to press auto-absorbance, auto-zero. So it's blanking using water. So now that it's blanked, I can actually remove my water, put my sample in, since it's in. So I'm going to go back to my home screen since it's in this mode. And then I'm going to measure my absorbance of my dye solution at 350 nanometers wavelength. So I go to go. And then it's going to record the absorbance. When it changes, you freeze the screen. You write down the absorbance value. And from there, you can actually determine your percentage transmittance by going back to the home screen, selecting the transmittance option, going to go. And then it will tell you your transmittance. So when the number changes, you actually record it. It's recording 95.4 transmittance, which is just about right. So you do this for your other samples. I'm just going to show you two samples as an example. So before you go to measure your other sample, which is going to be at 370, you need to blank again. So you have your water. So blanking is the same thing as saying you're performing the auto-zero option. So I go to the home screen, select spec 200 interface. And then I go to transmittance. And now I need to change my wavelength. So it's going to be 370. 370, oops, 370. And then I'm going to go to go. And then I'm going to perform my zero auto-zero. So when I've blanked, then I can put my sample in again. So now I'm going to get my absorbance and transmittance value for the sample at 370 nanometer wavelength. So I can record my transmittance since it's up on the screen right now. So let me go back to the home screen to make sure that I am recording. So since it's in the absorbance mode, let's go to that. And then we're going to measure the absorbance. And the absorbance here is 0.28, which is close to what we want. And then we're going to go to measure transmittance now. So we go back to home screen, select transmittance, hit Go. And it should measure it. And we got a measurement. So you record that. And if you were to do your third sample, then you have to blank first. Then you measure your absorbance and your transmittance of the third sample. And if you keep doing that from 350 to 650, you should get enough data points to plot your absorption spectrum.