WEBVTT 00:00:00.180 --> 00:00:02.220 - [Instructor] I have about 3.21 grams 00:00:02.220 --> 00:00:03.600 of sulfur powder over here. 00:00:03.600 --> 00:00:08.370 My question to you is how many atoms of sulfur are there? 00:00:08.370 --> 00:00:10.560 At first, this question sounds ridiculous. 00:00:10.560 --> 00:00:12.480 I mean, there's gonna be lots and lots of atoms. 00:00:12.480 --> 00:00:14.790 How in the world are we going to count that? 00:00:14.790 --> 00:00:18.210 That's what we're gonna find out in this video. 00:00:18.210 --> 00:00:21.180 We're gonna do that by introducing the idea of mole. 00:00:21.180 --> 00:00:22.380 So let's begin. 00:00:22.380 --> 00:00:24.000 To come up with the idea of moles, 00:00:24.000 --> 00:00:27.240 we first need a new unit of mass to deal 00:00:27.240 --> 00:00:28.620 with the masses of atoms. 00:00:28.620 --> 00:00:29.640 See, atoms are very tiny. 00:00:29.640 --> 00:00:31.410 Their masses are going to be incredibly tiny. 00:00:31.410 --> 00:00:33.270 So kilograms and grams is going 00:00:33.270 --> 00:00:35.250 to be very inconvenient to use. 00:00:35.250 --> 00:00:39.180 So we come up with a new unit called the atomic mass unit, 00:00:39.180 --> 00:00:40.590 AMU or u. 00:00:40.590 --> 00:00:42.420 It's a very tiny unit of mass. 00:00:42.420 --> 00:00:45.960 Just like grams or kilograms, it's a unit of mass. 00:00:45.960 --> 00:00:48.413 But, of course, whenever we learn about a new unit, 00:00:48.413 --> 00:00:51.570 we need to ask ourselves, "How big is that unit?" 00:00:51.570 --> 00:00:54.840 What is the definition of that unit? How big is 1u? 00:00:54.840 --> 00:00:56.855 Well, here's how we define what a u is. 00:00:56.855 --> 00:01:00.840 You take a single atom of carbon 12. 00:01:00.840 --> 00:01:05.840 Now, its mass by definition is 12u. 00:01:06.270 --> 00:01:07.770 This is not something that we have measured. 00:01:07.770 --> 00:01:09.330 This is something that we fixed. 00:01:09.330 --> 00:01:13.920 We fixed the mass of a carbon 12 atom to be two 12u. 00:01:13.920 --> 00:01:15.720 Exactly. Okay? 00:01:15.720 --> 00:01:17.820 Now, what is 1u? 00:01:17.820 --> 00:01:20.309 Well, if the mass of a carbon 12 atom is 12u, 00:01:20.309 --> 00:01:25.309 1u is 1/12 of its mass, right? 00:01:25.320 --> 00:01:30.320 So we define one atomic mass unit, 1u as 1/12 00:01:31.050 --> 00:01:35.670 of the mass of a single atom of the carbon 12 isotope. 00:01:35.670 --> 00:01:36.783 Does that make sense? 00:01:37.650 --> 00:01:38.670 Well, I'm sure at this point 00:01:38.670 --> 00:01:39.990 you may be having some questions, 00:01:39.990 --> 00:01:43.920 like why did we decide to use carbon as a reference 00:01:43.920 --> 00:01:45.450 and not any other elements? 00:01:45.450 --> 00:01:47.520 Well, it turns out that we actually started with hydrogen 00:01:47.520 --> 00:01:49.260 because it's one of the lightest elements. 00:01:49.260 --> 00:01:50.580 Then we ran into some problems 00:01:50.580 --> 00:01:52.560 and then we switched to oxygen 00:01:52.560 --> 00:01:54.810 because again, it's extremely abundant. 00:01:54.810 --> 00:01:56.400 Then again, we ran into some other problems, 00:01:56.400 --> 00:01:59.070 and then finally, we decided to go with carbon, 00:01:59.070 --> 00:02:00.720 which is also abundant. 00:02:00.720 --> 00:02:02.400 We'll not delve into the histories 00:02:02.400 --> 00:02:03.690 and details of what really happened, 00:02:03.690 --> 00:02:06.330 but yeah, we have to choose some element as a reference, 00:02:06.330 --> 00:02:09.180 and we ended up choosing carbon as a reference. 00:02:09.180 --> 00:02:10.230 Another question you could be having 00:02:10.230 --> 00:02:13.540 is why do we fix the mass of a single atom of this carbon 12 00:02:13.540 --> 00:02:15.030 to be 12u? 00:02:15.030 --> 00:02:17.340 Why not any other number? Why 12? 00:02:17.340 --> 00:02:18.570 Well, for that, you can see that over here. 00:02:18.570 --> 00:02:22.560 Carbon has how many protons and neutrons in it? 00:02:22.560 --> 00:02:26.040 Well, it has a total of, I mean, 00:02:26.040 --> 00:02:28.110 it has six protons and six neutrons. 00:02:28.110 --> 00:02:32.100 So it has a total of 12 protons and neutrons, 12 particles. 00:02:32.100 --> 00:02:34.170 I think of protons and neutrons together over here 00:02:34.170 --> 00:02:36.210 because they have pretty much similar mass. 00:02:36.210 --> 00:02:38.460 I mean, a neutron is actually slightly heavier 00:02:38.460 --> 00:02:40.440 than a proton, but for our purposes, 00:02:40.440 --> 00:02:42.750 to get an intuition over here, they're masses. 00:02:42.750 --> 00:02:44.040 We can pretty much think of them 00:02:44.040 --> 00:02:45.810 to be almost equal to each other. 00:02:45.810 --> 00:02:49.590 So it has a total of 12 particles, right? 00:02:49.590 --> 00:02:53.460 Now, by fixing the mass of those 12 particles to be 12u, 00:02:53.460 --> 00:02:54.300 look at what we are doing. 00:02:54.300 --> 00:02:56.700 We are basically saying, "Hey, 00:02:56.700 --> 00:02:59.430 let's fix the mass of a single proton 00:02:59.430 --> 00:03:02.370 or a neutron to be about 1u. 00:03:02.370 --> 00:03:04.740 That was the whole intention. Okay? 00:03:04.740 --> 00:03:09.210 So you can also think 1u is kind of a representation 00:03:09.210 --> 00:03:13.110 of a mass of a single proton or a neutron, 00:03:13.110 --> 00:03:16.410 but again, this is not exact because masses of protons 00:03:16.410 --> 00:03:19.800 and neutrons are not exactly equal to each other. 00:03:19.800 --> 00:03:22.890 So a proton and neutron will have a mass very close 00:03:22.890 --> 00:03:26.220 to 1u, but it's not exactly 1u, 00:03:26.220 --> 00:03:29.010 but it's a good way to think about what a u represents. 00:03:29.010 --> 00:03:32.100 It represents sort of the mass of a proton or neutron. 00:03:32.100 --> 00:03:34.830 Anyways, now that we understand this, here's a question. 00:03:34.830 --> 00:03:38.130 What do you think is the mass of a single atom 00:03:38.130 --> 00:03:40.050 of oxygen 16 isotope? 00:03:40.050 --> 00:03:41.220 A single atom of this, 00:03:41.220 --> 00:03:44.073 what will be its mass in u, atomic mass unit? 00:03:45.150 --> 00:03:48.480 Well, it has a total of 16 particles, 16 protons 00:03:48.480 --> 00:03:50.940 and neutrons together, and since each particle, 00:03:50.940 --> 00:03:52.920 each proton and neutron has a mass of 1u, 00:03:52.920 --> 00:03:57.810 and there are total 16, oxygen mass will be about 16u. 00:03:57.810 --> 00:04:00.330 Again, you can see it's not gonna be exactly 16u 00:04:00.330 --> 00:04:03.510 because mass of each proton and neutron is not exactly 1u, 00:04:03.510 --> 00:04:05.460 but it's gonna be very close to that. 00:04:05.460 --> 00:04:09.030 Similarly, if you take an isotope of say chlorine, 00:04:09.030 --> 00:04:11.310 a particular isotope, the most abundant isotope of fluorine, 00:04:11.310 --> 00:04:15.390 which has 35 protons and neutrons together in it, 00:04:15.390 --> 00:04:19.320 well, then its mass would be close to 35u. 00:04:19.320 --> 00:04:20.640 Makes sense, right? 00:04:20.640 --> 00:04:22.620 Okay, now, here's a question we're gonna ask ourselves. 00:04:22.620 --> 00:04:24.090 Let's go back to carbon. 00:04:24.090 --> 00:04:27.390 Each carbon has a mass of 12u, by definition. 00:04:27.390 --> 00:04:29.520 Now, how many carbon atoms do I need 00:04:29.520 --> 00:04:33.330 to take together says that the total mass of all 00:04:33.330 --> 00:04:37.140 of those carbon atoms together becomes 12 grams. 00:04:37.140 --> 00:04:39.690 You can imagine it's going to be lots 00:04:39.690 --> 00:04:40.800 and lots of atoms, right? 00:04:40.800 --> 00:04:43.920 Because each atom has a very tiny mass 00:04:43.920 --> 00:04:46.800 and we want together 12 grams. 00:04:46.800 --> 00:04:48.930 So we probably need to take billions 00:04:48.930 --> 00:04:50.430 and billions and billions of atoms. 00:04:50.430 --> 00:04:52.800 But the big question is how many atoms do I need to take 00:04:52.800 --> 00:04:56.250 is that they all add up to give me 12 grams of mass? 00:04:56.250 --> 00:04:58.560 Well, it turns out we figured it out. 00:04:58.560 --> 00:04:59.730 Again, we'll not get into the details 00:04:59.730 --> 00:05:01.350 of how we figured it out, okay? 00:05:01.350 --> 00:05:02.940 The history is actually pretty interesting, 00:05:02.940 --> 00:05:05.520 but again, we'll not talk about that over here, 00:05:05.520 --> 00:05:09.690 but we figured it out, and it turns out to be this number. 00:05:09.690 --> 00:05:12.240 You need to take about 6.022, 00:05:12.240 --> 00:05:13.800 and there are some other decimals over here, 00:05:13.800 --> 00:05:17.623 some numbers here, times 10 to the power 23, 00:05:19.410 --> 00:05:21.780 which is a huge number, okay? 00:05:21.780 --> 00:05:24.930 If you take these many carbon atoms together, 00:05:24.930 --> 00:05:28.410 carbon 12 atoms together, they will together have a mass 00:05:28.410 --> 00:05:31.110 of 12 grams. 00:05:31.110 --> 00:05:33.900 This number is what we call the Avogadro number 00:05:33.900 --> 00:05:36.630 named after the scientist Amedeo Avogadro 00:05:36.630 --> 00:05:38.190 who worked a lot on this idea. 00:05:38.190 --> 00:05:40.410 But anyways, you can now see the significance 00:05:40.410 --> 00:05:41.580 of this number. 00:05:41.580 --> 00:05:46.020 I can now count the number of atoms in a carbon isotope. 00:05:46.020 --> 00:05:48.030 If you give me 12 grams of carbon, 00:05:48.030 --> 00:05:51.750 I know it has these many number of carbon atoms in it. 00:05:51.750 --> 00:05:52.770 Carbon 12, okay? 00:05:52.770 --> 00:05:54.930 These many number of carbon 12 atoms in it. 00:05:54.930 --> 00:05:57.060 If you give me 24 grams of carbon, 00:05:57.060 --> 00:05:58.470 there must be twice the amount. 00:05:58.470 --> 00:06:00.240 If you give me six grams of carbon, 00:06:00.240 --> 00:06:01.890 then there must be half the amount. 00:06:01.890 --> 00:06:03.990 You tell me the mass of the carbon 12 isotope 00:06:03.990 --> 00:06:05.130 that I'm holding in my hand, 00:06:05.130 --> 00:06:07.410 and I can now use this number to tell you 00:06:07.410 --> 00:06:09.210 how many atoms there are. 00:06:09.210 --> 00:06:10.500 Beautiful, isn't it? 00:06:10.500 --> 00:06:13.770 In other words, this becomes the conversion factor 00:06:13.770 --> 00:06:17.640 for our tiny unit of mass, from our tiny unit of mass u 00:06:17.640 --> 00:06:20.340 to our more familiar big unit of mass, grams. 00:06:20.340 --> 00:06:24.030 If you take u and you multiply with this number, 00:06:24.030 --> 00:06:26.250 you get grams. 00:06:26.250 --> 00:06:29.880 And whenever you have an Avogadro number of things 00:06:29.880 --> 00:06:33.420 with you, we call it a mole. 00:06:33.420 --> 00:06:35.880 Just like how when you have 12 things with you, 00:06:35.880 --> 00:06:38.250 we call it a dozen, these many things, 00:06:38.250 --> 00:06:41.010 if you have together, it could be anything. 00:06:41.010 --> 00:06:42.510 It could be these many atoms. 00:06:42.510 --> 00:06:44.730 Then we'll call it a mole of atoms, 00:06:44.730 --> 00:06:46.410 or it could be these many babies. 00:06:46.410 --> 00:06:48.960 Then we'll say we have a mole of babies. 00:06:48.960 --> 00:06:51.180 It's a ridiculous number but you get the idea. 00:06:51.180 --> 00:06:55.080 And this word mole actually comes from the Latin molecule, 00:06:55.080 --> 00:06:58.590 which translates to a very tiny amount of something. 00:06:58.590 --> 00:07:00.540 But anyways, what is a mole? 00:07:00.540 --> 00:07:03.060 A mole represents Avogadro number, 00:07:03.060 --> 00:07:04.710 these many number of things. 00:07:04.710 --> 00:07:08.910 It could be number of atoms, molecules, particles, anything. 00:07:08.910 --> 00:07:10.620 And what's so special about this number? 00:07:10.620 --> 00:07:12.900 It's a conversion factor from the tiny unit 00:07:12.900 --> 00:07:14.400 of mass u to grams. 00:07:14.400 --> 00:07:16.230 You take this number, multiply it by this number, 00:07:16.230 --> 00:07:19.020 and you will now get it in grams. 00:07:19.020 --> 00:07:20.910 Okay, now, let's see if you understand this. 00:07:20.910 --> 00:07:24.000 What do you think would be the mass of one mole 00:07:24.000 --> 00:07:26.730 of oxygen 16 atoms? 00:07:26.730 --> 00:07:30.780 If I had an Avogadro number of oxygen 16 atoms together, 00:07:30.780 --> 00:07:33.230 what do you think collectively would its mass be? 00:07:34.560 --> 00:07:36.210 Well, an Avogadro number 00:07:36.210 --> 00:07:39.480 of 12us will give me a mass of 12 grams. 00:07:39.480 --> 00:07:41.610 So an Avogadro number of 16us 00:07:41.610 --> 00:07:44.820 will give me me a mass of 16 grams. 00:07:44.820 --> 00:07:47.610 That's what we mean by a conversion factor, okay? 00:07:47.610 --> 00:07:50.550 It works for any atom which has any mass. 00:07:50.550 --> 00:07:51.990 You just multiply it by this, 00:07:51.990 --> 00:07:55.680 and now you'll get the mass in grams. 00:07:55.680 --> 00:07:59.310 Similarly, if I had an Avogadro number of chlorine 35, 00:07:59.310 --> 00:08:02.760 if I had one more of chlorine 35 atoms with me, 00:08:02.760 --> 00:08:06.480 then it'll have 35 grams of mass. 00:08:06.480 --> 00:08:07.440 Make sense? 00:08:07.440 --> 00:08:09.600 And so another way to talk about all 00:08:09.600 --> 00:08:10.860 of these things, whatever I just said now, 00:08:10.860 --> 00:08:13.530 another way to talk about this is we say the molar mass 00:08:13.530 --> 00:08:16.350 of carbon 12 is 12 grams. 00:08:16.350 --> 00:08:21.030 Carbon 12 has a mass of 12 grams per mole. 00:08:21.030 --> 00:08:22.140 Makes sense, right? 00:08:22.140 --> 00:08:26.910 We would say oxygen 16 will have 16 grams per mole. 00:08:26.910 --> 00:08:28.320 I mention oxygen 16 00:08:28.320 --> 00:08:30.540 because remember, there are other isotopes as well. 00:08:30.540 --> 00:08:32.790 Different isotopes will have different masses, 00:08:32.790 --> 00:08:35.100 so their molar mass would be different. 00:08:35.100 --> 00:08:39.270 So oxygen 16 isotope has a molar mass 00:08:39.270 --> 00:08:41.820 of 16 grams per mole, 00:08:41.820 --> 00:08:45.300 and chlorine 35 has a molar mass 00:08:45.300 --> 00:08:47.850 of 35 grams per mole, okay? 00:08:47.850 --> 00:08:49.950 Same thing, whatever I just said, a technical way 00:08:49.950 --> 00:08:52.320 of stating the same thing over here. 00:08:52.320 --> 00:08:53.820 All right, the last thing we need to do 00:08:53.820 --> 00:08:55.980 to make this more practical is to remember 00:08:55.980 --> 00:08:58.560 that over here we considered pure cases. 00:08:58.560 --> 00:09:01.410 I took a pure carbon 12 isotopes 00:09:01.410 --> 00:09:03.480 where every single atom was carbon 12, 00:09:03.480 --> 00:09:05.370 or I took a pure chlorine isotope 00:09:05.370 --> 00:09:08.190 where every single atom was chlorine 35, 00:09:08.190 --> 00:09:09.840 but in reality, that's not the case. 00:09:09.840 --> 00:09:11.640 If I take a chunk of chlorine, 00:09:11.640 --> 00:09:13.290 a lot of it will be chlorine 35, 00:09:13.290 --> 00:09:15.870 but there'll be some other isotopes as well. 00:09:15.870 --> 00:09:18.540 Like, another abundant isotope next to chlorine 35 00:09:18.540 --> 00:09:20.670 is chlorine 37. 00:09:20.670 --> 00:09:23.220 And that sounds really complicated, but what's important 00:09:23.220 --> 00:09:25.320 and powerful is that that doesn't matter to us. 00:09:25.320 --> 00:09:27.300 This whole idea still works. Okay? 00:09:27.300 --> 00:09:28.170 Here's what I mean. 00:09:28.170 --> 00:09:29.310 Let me take an example. 00:09:29.310 --> 00:09:32.430 If you look at our periodic table, 00:09:32.430 --> 00:09:35.340 and you can see that the atomic mass of chlorine is given 00:09:35.340 --> 00:09:36.960 to be not 35. 00:09:36.960 --> 00:09:38.670 It's 35.45. 00:09:38.670 --> 00:09:41.377 So significant deviation from 35. Why? 00:09:41.377 --> 00:09:43.860 Because this also accounts for the fact 00:09:43.860 --> 00:09:45.090 that if you take a chunk of chlorine, 00:09:45.090 --> 00:09:48.570 it'll also contain a lot of chlorine 37 in it. 00:09:48.570 --> 00:09:50.460 So what we do is sort of like take an average. 00:09:50.460 --> 00:09:52.710 This is a weighted average, we say, 00:09:52.710 --> 00:09:55.800 so this is the average atomic mass of chlorine. 00:09:55.800 --> 00:09:57.210 So since I know the average atomic mass 00:09:57.210 --> 00:10:01.320 of chlorine is 35.45, if I now take one mole of chlorine, 00:10:01.320 --> 00:10:04.230 not pure as it exists as a mixture in nature, 00:10:04.230 --> 00:10:09.230 then one mole will have a mass of 35.45 grams. 00:10:09.600 --> 00:10:10.800 That's it. 00:10:10.800 --> 00:10:14.250 Similarly, if I take one mole of carbon, 00:10:14.250 --> 00:10:16.740 which, you know, it's not exactly 12 grams 00:10:16.740 --> 00:10:21.210 because there are other isotopes, it'll be 12.01 grams. 00:10:21.210 --> 00:10:24.120 You see what I mean? A mole is a conversion factor. 00:10:24.120 --> 00:10:28.890 Take one mole of anything, it'll be this number in grams. 00:10:28.890 --> 00:10:31.890 And so now we can try and answer our original question. 00:10:31.890 --> 00:10:35.460 We asked ourselves, if you have 3.21 grams of sulfur, 00:10:35.460 --> 00:10:37.020 how many atoms there are? 00:10:37.020 --> 00:10:38.225 Why don't you pause the video 00:10:38.225 --> 00:10:41.520 and see if you can now answer this question yourself. 00:10:41.520 --> 00:10:43.260 If I take one mole of sulfur, 00:10:43.260 --> 00:10:46.650 if I take Avogadro number of sulfur atoms, 00:10:46.650 --> 00:10:51.570 it'll have a mass of 32.1 grams, roughly 32.1 grams. 00:10:51.570 --> 00:10:54.780 So 32.1 grams represents one mole of sulfur. 00:10:54.780 --> 00:10:56.040 But how much sulfur do I have? 00:10:56.040 --> 00:10:59.190 I have not 32.1, I have 3.21 grams, 00:10:59.190 --> 00:11:02.327 which is just 1/10 of a mole. 00:11:02.327 --> 00:11:05.220 That's why I took 3.21 to just keep the calculation simpler. 00:11:05.220 --> 00:11:07.590 We can do it in our head. This is 1/10 of a mole. 00:11:07.590 --> 00:11:09.360 So how many atoms you must be having? 00:11:09.360 --> 00:11:13.680 1/10 of a mole, so 1/10 of the Avogadro number. 00:11:13.680 --> 00:11:16.020 So the answer would be the Avogadro number, 00:11:16.020 --> 00:11:18.540 which is 6.02 times 10 to the power 23 00:11:18.540 --> 00:11:20.160 divided by 10, 1/10 of it. 00:11:20.160 --> 00:11:23.283 So it'll be 6.02 times 10 to the power 22. 00:11:24.180 --> 00:11:25.650 Okay, here's our final question. 00:11:25.650 --> 00:11:27.802 If I take one mole of carbon dioxide, 00:11:27.802 --> 00:11:29.550 what do you think will its mass be? 00:11:29.550 --> 00:11:33.030 What is the molar mass of one mole of carbon dioxide? 00:11:33.030 --> 00:11:36.243 Can you pause the video and try to think about this? 00:11:37.500 --> 00:11:39.300 Okay, let's do this step by step. 00:11:39.300 --> 00:11:42.000 I know if I have one mole of carbon dioxide, 00:11:42.000 --> 00:11:47.000 then it must be having an Avogadro number of molecules 00:11:47.070 --> 00:11:48.960 of carbon dioxide, right? 00:11:48.960 --> 00:11:51.660 Remember, if I had half a mole of carbon dioxide, it means 00:11:51.660 --> 00:11:54.090 that I would have half the Avogadro number 00:11:54.090 --> 00:11:55.110 of carbon dioxide. 00:11:55.110 --> 00:11:56.100 Makes sense, right? Okay. 00:11:56.100 --> 00:11:57.840 Anyways, now comes the question 00:11:57.840 --> 00:11:59.640 how many carbon atoms must be there 00:11:59.640 --> 00:12:01.170 and how many oxygen atoms must be there? 00:12:01.170 --> 00:12:02.070 What do you think? 00:12:03.000 --> 00:12:05.520 Well, a single carbon dioxide molecule 00:12:05.520 --> 00:12:07.440 has one atom of carbon. 00:12:07.440 --> 00:12:10.860 If I have five molecules of carbon dioxide, 00:12:10.860 --> 00:12:13.260 I have five carbon atoms, 00:12:13.260 --> 00:12:14.790 which means if I have these many molecules 00:12:14.790 --> 00:12:18.210 of carbon dioxide, I should have exactly that many amount 00:12:18.210 --> 00:12:20.910 of carbon atoms, meaning I have one mole 00:12:20.910 --> 00:12:22.440 of carbon atoms with me. 00:12:22.440 --> 00:12:25.290 Okay, what about the number of oxygen atoms? 00:12:25.290 --> 00:12:30.290 Well, each carbon dioxide molecule has atoms of oxygen. 00:12:30.480 --> 00:12:33.120 And so if I had five, for example, molecules 00:12:33.120 --> 00:12:36.180 of carbon dioxide, I would have twice the amount, 00:12:36.180 --> 00:12:38.220 10 atoms of oxygen. 00:12:38.220 --> 00:12:40.470 And therefore, if I have these many molecules 00:12:40.470 --> 00:12:43.533 of carbon dioxide, I would have twice the amount, 00:12:44.790 --> 00:12:48.810 which means I have two moles of oxygen atoms with me. 00:12:48.810 --> 00:12:50.400 And I can now look at the periodic table 00:12:50.400 --> 00:12:52.950 to find the mass of one mole of carbon. 00:12:52.950 --> 00:12:57.420 It's 12.0107 grams, 00:12:57.420 --> 00:12:58.560 and for oxygen, 00:12:58.560 --> 00:13:02.490 it would be 15.9994 grams. 00:13:02.490 --> 00:13:04.440 That would be the mass of one mole of oxygen. 00:13:04.440 --> 00:13:06.300 But then we have to multiply it by two 00:13:06.300 --> 00:13:08.340 because over here, we have two moles. 00:13:08.340 --> 00:13:11.610 Simplifying this will give me the molar mass 00:13:11.610 --> 00:13:12.870 of carbon dioxide. 00:13:12.870 --> 00:13:16.680 So one mole of carbon dioxide will have this much mass. 00:13:16.680 --> 00:13:18.840 Or we can also say that carbon dioxide has a mass 00:13:18.840 --> 00:13:23.160 of 44.0095 grams per mole. 00:13:23.160 --> 00:13:24.930 Same thing. It's the same thing, okay? 00:13:24.930 --> 00:13:26.520 They all mean the same thing. 00:13:26.520 --> 00:13:27.510 Of course, we can round it off 00:13:27.510 --> 00:13:29.410 and we are actually doing a numerical.