What is the percent composition of cysteine, one of the 20 amino acids commonly found in proteins? (Gray = C, red = O, blue = N, yellow = S, ivory = H.)

Video transcript

Alright. So in this practice problem we have this molecule right here, which is a lean mean it's an amino acid. Used to make proteins for the molecule of valentin. We need to calculate the mass percent of nitrogen given this legend here. Okay, so we know which ones are nitrogen, which ones are oxygen? Carbon and hydrogen. So let's go ahead and count how many of each we have. So that we can go ahead and calculate the molar mass of this whole compound, a felony. And then we'll be able to find the mass percent of nitrogen. Right? Because mass percent of nitrogen is going to equal to mass of nitrogen within the compound divided by the total mass of that compound times 100. Okay, so we need to figure out the total mass of this compound and then the total mass of nitrogen to find the percentage. Alright, so for the nitrogen is we have blue and as we can see there's only one nitrogen. So nitrogen here We have one. If we take a look at the periodic table, nitrogen weighs 14.1 g. Okay, and there's only one of them. So it's just 14.01. Then we have read for oxygen. We have two of them. Okay, so we have two times it's smaller mass is going to be 16. So that will give us 32 total for the oxygen. Next we have carbon. How many carbons do we have? So the carbons are agree. So we have 12 and three. So we have three of them And they weighed 12. grams each. That will be 36.03g. And then finally, as hydrogen, the hydrogen is going to be the white the rest of them. So we have one, 23456 and seven. So it looks like we have seven hydrogen. So it's seven times its smaller mess which is 1.01. And that will give us 7.07. All right, so the total mass of this compound is going to be all of these masses just added together. And that will give us 89.11. And of course it's in g per one mole of this compound. Okay, so we have the smaller mass, which is the total mass of this compound. And we actually do have the mass of nitrogen because there's only one nitrogen here. So the total mass for nitrogen is just 14.1. So let's go ahead and plug in those numbers. So we're going to plug in this number and this number into this formula to find the mass percent. Alright, so nitrogen percent is going to be % .01g or g per mole divided by the total mass, which is the molar mass Of this whole compound and then times 100. Alright, so divide multiply and we should get 15.7 as the answer to this problem. Okay, so there's 15.7% of nitrogen within the compound. Alunan. Alright folks, thank you so much for watching, and we'll see you in the next video.