[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.18,0:00:02.22,Default,,0000,0000,0000,,- [Instructor] I have about 3.21 grams
Dialogue: 0,0:00:02.22,0:00:03.60,Default,,0000,0000,0000,,of sulfur powder over here.
Dialogue: 0,0:00:03.60,0:00:08.37,Default,,0000,0000,0000,,My question to you is how many\Natoms of sulfur are there?
Dialogue: 0,0:00:08.37,0:00:10.56,Default,,0000,0000,0000,,At first, this question sounds ridiculous.
Dialogue: 0,0:00:10.56,0:00:12.48,Default,,0000,0000,0000,,I mean, there's gonna be\Nlots and lots of atoms.
Dialogue: 0,0:00:12.48,0:00:14.79,Default,,0000,0000,0000,,How in the world are\Nwe going to count that?
Dialogue: 0,0:00:14.79,0:00:18.21,Default,,0000,0000,0000,,That's what we're gonna\Nfind out in this video.
Dialogue: 0,0:00:18.21,0:00:21.18,Default,,0000,0000,0000,,We're gonna do that by\Nintroducing the idea of mole.
Dialogue: 0,0:00:21.18,0:00:22.38,Default,,0000,0000,0000,,So let's begin.
Dialogue: 0,0:00:22.38,0:00:24.00,Default,,0000,0000,0000,,To come up with the idea of moles,
Dialogue: 0,0:00:24.00,0:00:27.24,Default,,0000,0000,0000,,we first need a new unit of mass to deal
Dialogue: 0,0:00:27.24,0:00:28.62,Default,,0000,0000,0000,,with the masses of atoms.
Dialogue: 0,0:00:28.62,0:00:29.64,Default,,0000,0000,0000,,See, atoms are very tiny.
Dialogue: 0,0:00:29.64,0:00:31.41,Default,,0000,0000,0000,,Their masses are going\Nto be incredibly tiny.
Dialogue: 0,0:00:31.41,0:00:33.27,Default,,0000,0000,0000,,So kilograms and grams is going
Dialogue: 0,0:00:33.27,0:00:35.25,Default,,0000,0000,0000,,to be very inconvenient to use.
Dialogue: 0,0:00:35.25,0:00:39.18,Default,,0000,0000,0000,,So we come up with a new unit\Ncalled the atomic mass unit,
Dialogue: 0,0:00:39.18,0:00:40.59,Default,,0000,0000,0000,,AMU or u.
Dialogue: 0,0:00:40.59,0:00:42.42,Default,,0000,0000,0000,,It's a very tiny unit of mass.
Dialogue: 0,0:00:42.42,0:00:45.96,Default,,0000,0000,0000,,Just like grams or kilograms,\Nit's a unit of mass.
Dialogue: 0,0:00:45.96,0:00:48.41,Default,,0000,0000,0000,,But, of course, whenever\Nwe learn about a new unit,
Dialogue: 0,0:00:48.41,0:00:51.57,Default,,0000,0000,0000,,we need to ask ourselves,\N"How big is that unit?"
Dialogue: 0,0:00:51.57,0:00:54.84,Default,,0000,0000,0000,,What is the definition of\Nthat unit? How big is 1u?
Dialogue: 0,0:00:54.84,0:00:56.86,Default,,0000,0000,0000,,Well, here's how we define what a u is.
Dialogue: 0,0:00:56.86,0:01:00.84,Default,,0000,0000,0000,,You take a single atom of carbon 12.
Dialogue: 0,0:01:00.84,0:01:05.84,Default,,0000,0000,0000,,Now, its mass by definition is 12u.
Dialogue: 0,0:01:06.27,0:01:07.77,Default,,0000,0000,0000,,This is not something\Nthat we have measured.
Dialogue: 0,0:01:07.77,0:01:09.33,Default,,0000,0000,0000,,This is something that we fixed.
Dialogue: 0,0:01:09.33,0:01:13.92,Default,,0000,0000,0000,,We fixed the mass of a\Ncarbon 12 atom to be two 12u.
Dialogue: 0,0:01:13.92,0:01:15.72,Default,,0000,0000,0000,,Exactly. Okay?
Dialogue: 0,0:01:15.72,0:01:17.82,Default,,0000,0000,0000,,Now, what is 1u?
Dialogue: 0,0:01:17.82,0:01:20.31,Default,,0000,0000,0000,,Well, if the mass of a\Ncarbon 12 atom is 12u,
Dialogue: 0,0:01:20.31,0:01:25.31,Default,,0000,0000,0000,,1u is 1/12 of its mass, right?
Dialogue: 0,0:01:25.32,0:01:30.32,Default,,0000,0000,0000,,So we define one atomic\Nmass unit, 1u as 1/12
Dialogue: 0,0:01:31.05,0:01:35.67,Default,,0000,0000,0000,,of the mass of a single atom\Nof the carbon 12 isotope.
Dialogue: 0,0:01:35.67,0:01:36.78,Default,,0000,0000,0000,,Does that make sense?
Dialogue: 0,0:01:37.65,0:01:38.67,Default,,0000,0000,0000,,Well, I'm sure at this point
Dialogue: 0,0:01:38.67,0:01:39.99,Default,,0000,0000,0000,,you may be having some questions,
Dialogue: 0,0:01:39.99,0:01:43.92,Default,,0000,0000,0000,,like why did we decide to\Nuse carbon as a reference
Dialogue: 0,0:01:43.92,0:01:45.45,Default,,0000,0000,0000,,and not any other elements?
Dialogue: 0,0:01:45.45,0:01:47.52,Default,,0000,0000,0000,,Well, it turns out that we\Nactually started with hydrogen
Dialogue: 0,0:01:47.52,0:01:49.26,Default,,0000,0000,0000,,because it's one of the lightest elements.
Dialogue: 0,0:01:49.26,0:01:50.58,Default,,0000,0000,0000,,Then we ran into some problems
Dialogue: 0,0:01:50.58,0:01:52.56,Default,,0000,0000,0000,,and then we switched to oxygen
Dialogue: 0,0:01:52.56,0:01:54.81,Default,,0000,0000,0000,,because again, it's extremely abundant.
Dialogue: 0,0:01:54.81,0:01:56.40,Default,,0000,0000,0000,,Then again, we ran into\Nsome other problems,
Dialogue: 0,0:01:56.40,0:01:59.07,Default,,0000,0000,0000,,and then finally, we\Ndecided to go with carbon,
Dialogue: 0,0:01:59.07,0:02:00.72,Default,,0000,0000,0000,,which is also abundant.
Dialogue: 0,0:02:00.72,0:02:02.40,Default,,0000,0000,0000,,We'll not delve into the histories
Dialogue: 0,0:02:02.40,0:02:03.69,Default,,0000,0000,0000,,and details of what really happened,
Dialogue: 0,0:02:03.69,0:02:06.33,Default,,0000,0000,0000,,but yeah, we have to choose\Nsome element as a reference,
Dialogue: 0,0:02:06.33,0:02:09.18,Default,,0000,0000,0000,,and we ended up choosing\Ncarbon as a reference.
Dialogue: 0,0:02:09.18,0:02:10.23,Default,,0000,0000,0000,,Another question you could be having
Dialogue: 0,0:02:10.23,0:02:13.54,Default,,0000,0000,0000,,is why do we fix the mass of a\Nsingle atom of this carbon 12
Dialogue: 0,0:02:13.54,0:02:15.03,Default,,0000,0000,0000,,to be 12u?
Dialogue: 0,0:02:15.03,0:02:17.34,Default,,0000,0000,0000,,Why not any other number? Why 12?
Dialogue: 0,0:02:17.34,0:02:18.57,Default,,0000,0000,0000,,Well, for that, you\Ncan see that over here.
Dialogue: 0,0:02:18.57,0:02:22.56,Default,,0000,0000,0000,,Carbon has how many\Nprotons and neutrons in it?
Dialogue: 0,0:02:22.56,0:02:26.04,Default,,0000,0000,0000,,Well, it has a total of, I mean,
Dialogue: 0,0:02:26.04,0:02:28.11,Default,,0000,0000,0000,,it has six protons and six neutrons.
Dialogue: 0,0:02:28.11,0:02:32.10,Default,,0000,0000,0000,,So it has a total of 12 protons\Nand neutrons, 12 particles.
Dialogue: 0,0:02:32.10,0:02:34.17,Default,,0000,0000,0000,,I think of protons and\Nneutrons together over here
Dialogue: 0,0:02:34.17,0:02:36.21,Default,,0000,0000,0000,,because they have pretty\Nmuch similar mass.
Dialogue: 0,0:02:36.21,0:02:38.46,Default,,0000,0000,0000,,I mean, a neutron is\Nactually slightly heavier
Dialogue: 0,0:02:38.46,0:02:40.44,Default,,0000,0000,0000,,than a proton, but for our purposes,
Dialogue: 0,0:02:40.44,0:02:42.75,Default,,0000,0000,0000,,to get an intuition over\Nhere, they're masses.
Dialogue: 0,0:02:42.75,0:02:44.04,Default,,0000,0000,0000,,We can pretty much think of them
Dialogue: 0,0:02:44.04,0:02:45.81,Default,,0000,0000,0000,,to be almost equal to each other.
Dialogue: 0,0:02:45.81,0:02:49.59,Default,,0000,0000,0000,,So it has a total of 12 particles, right?
Dialogue: 0,0:02:49.59,0:02:53.46,Default,,0000,0000,0000,,Now, by fixing the mass of\Nthose 12 particles to be 12u,
Dialogue: 0,0:02:53.46,0:02:54.30,Default,,0000,0000,0000,,look at what we are doing.
Dialogue: 0,0:02:54.30,0:02:56.70,Default,,0000,0000,0000,,We are basically saying, "Hey,
Dialogue: 0,0:02:56.70,0:02:59.43,Default,,0000,0000,0000,,let's fix the mass of a single proton
Dialogue: 0,0:02:59.43,0:03:02.37,Default,,0000,0000,0000,,or a neutron to be about 1u.
Dialogue: 0,0:03:02.37,0:03:04.74,Default,,0000,0000,0000,,That was the whole intention. Okay?
Dialogue: 0,0:03:04.74,0:03:09.21,Default,,0000,0000,0000,,So you can also think 1u\Nis kind of a representation
Dialogue: 0,0:03:09.21,0:03:13.11,Default,,0000,0000,0000,,of a mass of a single proton or a neutron,
Dialogue: 0,0:03:13.11,0:03:16.41,Default,,0000,0000,0000,,but again, this is not exact\Nbecause masses of protons
Dialogue: 0,0:03:16.41,0:03:19.80,Default,,0000,0000,0000,,and neutrons are not\Nexactly equal to each other.
Dialogue: 0,0:03:19.80,0:03:22.89,Default,,0000,0000,0000,,So a proton and neutron\Nwill have a mass very close
Dialogue: 0,0:03:22.89,0:03:26.22,Default,,0000,0000,0000,,to 1u, but it's not exactly 1u,
Dialogue: 0,0:03:26.22,0:03:29.01,Default,,0000,0000,0000,,but it's a good way to think\Nabout what a u represents.
Dialogue: 0,0:03:29.01,0:03:32.10,Default,,0000,0000,0000,,It represents sort of the\Nmass of a proton or neutron.
Dialogue: 0,0:03:32.10,0:03:34.83,Default,,0000,0000,0000,,Anyways, now that we understand\Nthis, here's a question.
Dialogue: 0,0:03:34.83,0:03:38.13,Default,,0000,0000,0000,,What do you think is the\Nmass of a single atom
Dialogue: 0,0:03:38.13,0:03:40.05,Default,,0000,0000,0000,,of oxygen 16 isotope?
Dialogue: 0,0:03:40.05,0:03:41.22,Default,,0000,0000,0000,,A single atom of this,
Dialogue: 0,0:03:41.22,0:03:44.07,Default,,0000,0000,0000,,what will be its mass\Nin u, atomic mass unit?
Dialogue: 0,0:03:45.15,0:03:48.48,Default,,0000,0000,0000,,Well, it has a total of\N16 particles, 16 protons
Dialogue: 0,0:03:48.48,0:03:50.94,Default,,0000,0000,0000,,and neutrons together,\Nand since each particle,
Dialogue: 0,0:03:50.94,0:03:52.92,Default,,0000,0000,0000,,each proton and neutron has a mass of 1u,
Dialogue: 0,0:03:52.92,0:03:57.81,Default,,0000,0000,0000,,and there are total 16,\Noxygen mass will be about 16u.
Dialogue: 0,0:03:57.81,0:04:00.33,Default,,0000,0000,0000,,Again, you can see it's\Nnot gonna be exactly 16u
Dialogue: 0,0:04:00.33,0:04:03.51,Default,,0000,0000,0000,,because mass of each proton\Nand neutron is not exactly 1u,
Dialogue: 0,0:04:03.51,0:04:05.46,Default,,0000,0000,0000,,but it's gonna be very close to that.
Dialogue: 0,0:04:05.46,0:04:09.03,Default,,0000,0000,0000,,Similarly, if you take an\Nisotope of say chlorine,
Dialogue: 0,0:04:09.03,0:04:11.31,Default,,0000,0000,0000,,a particular isotope, the most\Nabundant isotope of fluorine,
Dialogue: 0,0:04:11.31,0:04:15.39,Default,,0000,0000,0000,,which has 35 protons and\Nneutrons together in it,
Dialogue: 0,0:04:15.39,0:04:19.32,Default,,0000,0000,0000,,well, then its mass would be close to 35u.
Dialogue: 0,0:04:19.32,0:04:20.64,Default,,0000,0000,0000,,Makes sense, right?
Dialogue: 0,0:04:20.64,0:04:22.62,Default,,0000,0000,0000,,Okay, now, here's a question\Nwe're gonna ask ourselves.
Dialogue: 0,0:04:22.62,0:04:24.09,Default,,0000,0000,0000,,Let's go back to carbon.
Dialogue: 0,0:04:24.09,0:04:27.39,Default,,0000,0000,0000,,Each carbon has a mass\Nof 12u, by definition.
Dialogue: 0,0:04:27.39,0:04:29.52,Default,,0000,0000,0000,,Now, how many carbon atoms do I need
Dialogue: 0,0:04:29.52,0:04:33.33,Default,,0000,0000,0000,,to take together says\Nthat the total mass of all
Dialogue: 0,0:04:33.33,0:04:37.14,Default,,0000,0000,0000,,of those carbon atoms\Ntogether becomes 12 grams.
Dialogue: 0,0:04:37.14,0:04:39.69,Default,,0000,0000,0000,,You can imagine it's going to be lots
Dialogue: 0,0:04:39.69,0:04:40.80,Default,,0000,0000,0000,,and lots of atoms, right?
Dialogue: 0,0:04:40.80,0:04:43.92,Default,,0000,0000,0000,,Because each atom has a very tiny mass
Dialogue: 0,0:04:43.92,0:04:46.80,Default,,0000,0000,0000,,and we want together 12 grams.
Dialogue: 0,0:04:46.80,0:04:48.93,Default,,0000,0000,0000,,So we probably need to take billions
Dialogue: 0,0:04:48.93,0:04:50.43,Default,,0000,0000,0000,,and billions and billions of atoms.
Dialogue: 0,0:04:50.43,0:04:52.80,Default,,0000,0000,0000,,But the big question is how\Nmany atoms do I need to take
Dialogue: 0,0:04:52.80,0:04:56.25,Default,,0000,0000,0000,,is that they all add up to\Ngive me 12 grams of mass?
Dialogue: 0,0:04:56.25,0:04:58.56,Default,,0000,0000,0000,,Well, it turns out we figured it out.
Dialogue: 0,0:04:58.56,0:04:59.73,Default,,0000,0000,0000,,Again, we'll not get into the details
Dialogue: 0,0:04:59.73,0:05:01.35,Default,,0000,0000,0000,,of how we figured it out, okay?
Dialogue: 0,0:05:01.35,0:05:02.94,Default,,0000,0000,0000,,The history is actually\Npretty interesting,
Dialogue: 0,0:05:02.94,0:05:05.52,Default,,0000,0000,0000,,but again, we'll not talk\Nabout that over here,
Dialogue: 0,0:05:05.52,0:05:09.69,Default,,0000,0000,0000,,but we figured it out, and it\Nturns out to be this number.
Dialogue: 0,0:05:09.69,0:05:12.24,Default,,0000,0000,0000,,You need to take about 6.022,
Dialogue: 0,0:05:12.24,0:05:13.80,Default,,0000,0000,0000,,and there are some other\Ndecimals over here,
Dialogue: 0,0:05:13.80,0:05:17.62,Default,,0000,0000,0000,,some numbers here, times\N10 to the power 23,
Dialogue: 0,0:05:19.41,0:05:21.78,Default,,0000,0000,0000,,which is a huge number, okay?
Dialogue: 0,0:05:21.78,0:05:24.93,Default,,0000,0000,0000,,If you take these many\Ncarbon atoms together,
Dialogue: 0,0:05:24.93,0:05:28.41,Default,,0000,0000,0000,,carbon 12 atoms together,\Nthey will together have a mass
Dialogue: 0,0:05:28.41,0:05:31.11,Default,,0000,0000,0000,,of 12 grams.
Dialogue: 0,0:05:31.11,0:05:33.90,Default,,0000,0000,0000,,This number is what we\Ncall the Avogadro number
Dialogue: 0,0:05:33.90,0:05:36.63,Default,,0000,0000,0000,,named after the scientist Amedeo Avogadro
Dialogue: 0,0:05:36.63,0:05:38.19,Default,,0000,0000,0000,,who worked a lot on this idea.
Dialogue: 0,0:05:38.19,0:05:40.41,Default,,0000,0000,0000,,But anyways, you can\Nnow see the significance
Dialogue: 0,0:05:40.41,0:05:41.58,Default,,0000,0000,0000,,of this number.
Dialogue: 0,0:05:41.58,0:05:46.02,Default,,0000,0000,0000,,I can now count the number\Nof atoms in a carbon isotope.
Dialogue: 0,0:05:46.02,0:05:48.03,Default,,0000,0000,0000,,If you give me 12 grams of carbon,
Dialogue: 0,0:05:48.03,0:05:51.75,Default,,0000,0000,0000,,I know it has these many\Nnumber of carbon atoms in it.
Dialogue: 0,0:05:51.75,0:05:52.77,Default,,0000,0000,0000,,Carbon 12, okay?
Dialogue: 0,0:05:52.77,0:05:54.93,Default,,0000,0000,0000,,These many number of\Ncarbon 12 atoms in it.
Dialogue: 0,0:05:54.93,0:05:57.06,Default,,0000,0000,0000,,If you give me 24 grams of carbon,
Dialogue: 0,0:05:57.06,0:05:58.47,Default,,0000,0000,0000,,there must be twice the amount.
Dialogue: 0,0:05:58.47,0:06:00.24,Default,,0000,0000,0000,,If you give me six grams of carbon,
Dialogue: 0,0:06:00.24,0:06:01.89,Default,,0000,0000,0000,,then there must be half the amount.
Dialogue: 0,0:06:01.89,0:06:03.99,Default,,0000,0000,0000,,You tell me the mass of\Nthe carbon 12 isotope
Dialogue: 0,0:06:03.99,0:06:05.13,Default,,0000,0000,0000,,that I'm holding in my hand,
Dialogue: 0,0:06:05.13,0:06:07.41,Default,,0000,0000,0000,,and I can now use this number to tell you
Dialogue: 0,0:06:07.41,0:06:09.21,Default,,0000,0000,0000,,how many atoms there are.
Dialogue: 0,0:06:09.21,0:06:10.50,Default,,0000,0000,0000,,Beautiful, isn't it?
Dialogue: 0,0:06:10.50,0:06:13.77,Default,,0000,0000,0000,,In other words, this becomes\Nthe conversion factor
Dialogue: 0,0:06:13.77,0:06:17.64,Default,,0000,0000,0000,,for our tiny unit of mass,\Nfrom our tiny unit of mass u
Dialogue: 0,0:06:17.64,0:06:20.34,Default,,0000,0000,0000,,to our more familiar\Nbig unit of mass, grams.
Dialogue: 0,0:06:20.34,0:06:24.03,Default,,0000,0000,0000,,If you take u and you\Nmultiply with this number,
Dialogue: 0,0:06:24.03,0:06:26.25,Default,,0000,0000,0000,,you get grams.
Dialogue: 0,0:06:26.25,0:06:29.88,Default,,0000,0000,0000,,And whenever you have an\NAvogadro number of things
Dialogue: 0,0:06:29.88,0:06:33.42,Default,,0000,0000,0000,,with you, we call it a mole.
Dialogue: 0,0:06:33.42,0:06:35.88,Default,,0000,0000,0000,,Just like how when you\Nhave 12 things with you,
Dialogue: 0,0:06:35.88,0:06:38.25,Default,,0000,0000,0000,,we call it a dozen, these many things,
Dialogue: 0,0:06:38.25,0:06:41.01,Default,,0000,0000,0000,,if you have together,\Nit could be anything.
Dialogue: 0,0:06:41.01,0:06:42.51,Default,,0000,0000,0000,,It could be these many atoms.
Dialogue: 0,0:06:42.51,0:06:44.73,Default,,0000,0000,0000,,Then we'll call it a mole of atoms,
Dialogue: 0,0:06:44.73,0:06:46.41,Default,,0000,0000,0000,,or it could be these many babies.
Dialogue: 0,0:06:46.41,0:06:48.96,Default,,0000,0000,0000,,Then we'll say we have a mole of babies.
Dialogue: 0,0:06:48.96,0:06:51.18,Default,,0000,0000,0000,,It's a ridiculous number\Nbut you get the idea.
Dialogue: 0,0:06:51.18,0:06:55.08,Default,,0000,0000,0000,,And this word mole actually\Ncomes from the Latin molecule,
Dialogue: 0,0:06:55.08,0:06:58.59,Default,,0000,0000,0000,,which translates to a very\Ntiny amount of something.
Dialogue: 0,0:06:58.59,0:07:00.54,Default,,0000,0000,0000,,But anyways, what is a mole?
Dialogue: 0,0:07:00.54,0:07:03.06,Default,,0000,0000,0000,,A mole represents Avogadro number,
Dialogue: 0,0:07:03.06,0:07:04.71,Default,,0000,0000,0000,,these many number of things.
Dialogue: 0,0:07:04.71,0:07:08.91,Default,,0000,0000,0000,,It could be number of atoms,\Nmolecules, particles, anything.
Dialogue: 0,0:07:08.91,0:07:10.62,Default,,0000,0000,0000,,And what's so special about this number?
Dialogue: 0,0:07:10.62,0:07:12.90,Default,,0000,0000,0000,,It's a conversion factor\Nfrom the tiny unit
Dialogue: 0,0:07:12.90,0:07:14.40,Default,,0000,0000,0000,,of mass u to grams.
Dialogue: 0,0:07:14.40,0:07:16.23,Default,,0000,0000,0000,,You take this number,\Nmultiply it by this number,
Dialogue: 0,0:07:16.23,0:07:19.02,Default,,0000,0000,0000,,and you will now get it in grams.
Dialogue: 0,0:07:19.02,0:07:20.91,Default,,0000,0000,0000,,Okay, now, let's see\Nif you understand this.
Dialogue: 0,0:07:20.91,0:07:24.00,Default,,0000,0000,0000,,What do you think would\Nbe the mass of one mole
Dialogue: 0,0:07:24.00,0:07:26.73,Default,,0000,0000,0000,,of oxygen 16 atoms?
Dialogue: 0,0:07:26.73,0:07:30.78,Default,,0000,0000,0000,,If I had an Avogadro number\Nof oxygen 16 atoms together,
Dialogue: 0,0:07:30.78,0:07:33.23,Default,,0000,0000,0000,,what do you think collectively\Nwould its mass be?
Dialogue: 0,0:07:34.56,0:07:36.21,Default,,0000,0000,0000,,Well, an Avogadro number
Dialogue: 0,0:07:36.21,0:07:39.48,Default,,0000,0000,0000,,of 12us will give me a mass of 12 grams.
Dialogue: 0,0:07:39.48,0:07:41.61,Default,,0000,0000,0000,,So an Avogadro number of 16us
Dialogue: 0,0:07:41.61,0:07:44.82,Default,,0000,0000,0000,,will give me me a mass of 16 grams.
Dialogue: 0,0:07:44.82,0:07:47.61,Default,,0000,0000,0000,,That's what we mean by a\Nconversion factor, okay?
Dialogue: 0,0:07:47.61,0:07:50.55,Default,,0000,0000,0000,,It works for any atom which has any mass.
Dialogue: 0,0:07:50.55,0:07:51.99,Default,,0000,0000,0000,,You just multiply it by this,
Dialogue: 0,0:07:51.99,0:07:55.68,Default,,0000,0000,0000,,and now you'll get the mass in grams.
Dialogue: 0,0:07:55.68,0:07:59.31,Default,,0000,0000,0000,,Similarly, if I had an\NAvogadro number of chlorine 35,
Dialogue: 0,0:07:59.31,0:08:02.76,Default,,0000,0000,0000,,if I had one more of\Nchlorine 35 atoms with me,
Dialogue: 0,0:08:02.76,0:08:06.48,Default,,0000,0000,0000,,then it'll have 35 grams of mass.
Dialogue: 0,0:08:06.48,0:08:07.44,Default,,0000,0000,0000,,Make sense?
Dialogue: 0,0:08:07.44,0:08:09.60,Default,,0000,0000,0000,,And so another way to talk about all
Dialogue: 0,0:08:09.60,0:08:10.86,Default,,0000,0000,0000,,of these things, whatever I just said now,
Dialogue: 0,0:08:10.86,0:08:13.53,Default,,0000,0000,0000,,another way to talk about\Nthis is we say the molar mass
Dialogue: 0,0:08:13.53,0:08:16.35,Default,,0000,0000,0000,,of carbon 12 is 12 grams.
Dialogue: 0,0:08:16.35,0:08:21.03,Default,,0000,0000,0000,,Carbon 12 has a mass of 12 grams per mole.
Dialogue: 0,0:08:21.03,0:08:22.14,Default,,0000,0000,0000,,Makes sense, right?
Dialogue: 0,0:08:22.14,0:08:26.91,Default,,0000,0000,0000,,We would say oxygen 16 will\Nhave 16 grams per mole.
Dialogue: 0,0:08:26.91,0:08:28.32,Default,,0000,0000,0000,,I mention oxygen 16
Dialogue: 0,0:08:28.32,0:08:30.54,Default,,0000,0000,0000,,because remember, there\Nare other isotopes as well.
Dialogue: 0,0:08:30.54,0:08:32.79,Default,,0000,0000,0000,,Different isotopes will\Nhave different masses,
Dialogue: 0,0:08:32.79,0:08:35.10,Default,,0000,0000,0000,,so their molar mass would be different.
Dialogue: 0,0:08:35.10,0:08:39.27,Default,,0000,0000,0000,,So oxygen 16 isotope has a molar mass
Dialogue: 0,0:08:39.27,0:08:41.82,Default,,0000,0000,0000,,of 16 grams per mole,
Dialogue: 0,0:08:41.82,0:08:45.30,Default,,0000,0000,0000,,and chlorine 35 has a molar mass
Dialogue: 0,0:08:45.30,0:08:47.85,Default,,0000,0000,0000,,of 35 grams per mole, okay?
Dialogue: 0,0:08:47.85,0:08:49.95,Default,,0000,0000,0000,,Same thing, whatever I\Njust said, a technical way
Dialogue: 0,0:08:49.95,0:08:52.32,Default,,0000,0000,0000,,of stating the same thing over here.
Dialogue: 0,0:08:52.32,0:08:53.82,Default,,0000,0000,0000,,All right, the last thing we need to do
Dialogue: 0,0:08:53.82,0:08:55.98,Default,,0000,0000,0000,,to make this more practical is to remember
Dialogue: 0,0:08:55.98,0:08:58.56,Default,,0000,0000,0000,,that over here we considered pure cases.
Dialogue: 0,0:08:58.56,0:09:01.41,Default,,0000,0000,0000,,I took a pure carbon 12 isotopes
Dialogue: 0,0:09:01.41,0:09:03.48,Default,,0000,0000,0000,,where every single atom was carbon 12,
Dialogue: 0,0:09:03.48,0:09:05.37,Default,,0000,0000,0000,,or I took a pure chlorine isotope
Dialogue: 0,0:09:05.37,0:09:08.19,Default,,0000,0000,0000,,where every single atom was chlorine 35,
Dialogue: 0,0:09:08.19,0:09:09.84,Default,,0000,0000,0000,,but in reality, that's not the case.
Dialogue: 0,0:09:09.84,0:09:11.64,Default,,0000,0000,0000,,If I take a chunk of chlorine,
Dialogue: 0,0:09:11.64,0:09:13.29,Default,,0000,0000,0000,,a lot of it will be chlorine 35,
Dialogue: 0,0:09:13.29,0:09:15.87,Default,,0000,0000,0000,,but there'll be some\Nother isotopes as well.
Dialogue: 0,0:09:15.87,0:09:18.54,Default,,0000,0000,0000,,Like, another abundant\Nisotope next to chlorine 35
Dialogue: 0,0:09:18.54,0:09:20.67,Default,,0000,0000,0000,,is chlorine 37.
Dialogue: 0,0:09:20.67,0:09:23.22,Default,,0000,0000,0000,,And that sounds really\Ncomplicated, but what's important
Dialogue: 0,0:09:23.22,0:09:25.32,Default,,0000,0000,0000,,and powerful is that that\Ndoesn't matter to us.
Dialogue: 0,0:09:25.32,0:09:27.30,Default,,0000,0000,0000,,This whole idea still works. Okay?
Dialogue: 0,0:09:27.30,0:09:28.17,Default,,0000,0000,0000,,Here's what I mean.
Dialogue: 0,0:09:28.17,0:09:29.31,Default,,0000,0000,0000,,Let me take an example.
Dialogue: 0,0:09:29.31,0:09:32.43,Default,,0000,0000,0000,,If you look at our periodic table,
Dialogue: 0,0:09:32.43,0:09:35.34,Default,,0000,0000,0000,,and you can see that the atomic\Nmass of chlorine is given
Dialogue: 0,0:09:35.34,0:09:36.96,Default,,0000,0000,0000,,to be not 35.
Dialogue: 0,0:09:36.96,0:09:38.67,Default,,0000,0000,0000,,It's 35.45.
Dialogue: 0,0:09:38.67,0:09:41.38,Default,,0000,0000,0000,,So significant deviation from 35. Why?
Dialogue: 0,0:09:41.38,0:09:43.86,Default,,0000,0000,0000,,Because this also accounts for the fact
Dialogue: 0,0:09:43.86,0:09:45.09,Default,,0000,0000,0000,,that if you take a chunk of chlorine,
Dialogue: 0,0:09:45.09,0:09:48.57,Default,,0000,0000,0000,,it'll also contain a lot\Nof chlorine 37 in it.
Dialogue: 0,0:09:48.57,0:09:50.46,Default,,0000,0000,0000,,So what we do is sort\Nof like take an average.
Dialogue: 0,0:09:50.46,0:09:52.71,Default,,0000,0000,0000,,This is a weighted average, we say,
Dialogue: 0,0:09:52.71,0:09:55.80,Default,,0000,0000,0000,,so this is the average\Natomic mass of chlorine.
Dialogue: 0,0:09:55.80,0:09:57.21,Default,,0000,0000,0000,,So since I know the average atomic mass
Dialogue: 0,0:09:57.21,0:10:01.32,Default,,0000,0000,0000,,of chlorine is 35.45, if I\Nnow take one mole of chlorine,
Dialogue: 0,0:10:01.32,0:10:04.23,Default,,0000,0000,0000,,not pure as it exists\Nas a mixture in nature,
Dialogue: 0,0:10:04.23,0:10:09.23,Default,,0000,0000,0000,,then one mole will have\Na mass of 35.45 grams.
Dialogue: 0,0:10:09.60,0:10:10.80,Default,,0000,0000,0000,,That's it.
Dialogue: 0,0:10:10.80,0:10:14.25,Default,,0000,0000,0000,,Similarly, if I take one mole of carbon,
Dialogue: 0,0:10:14.25,0:10:16.74,Default,,0000,0000,0000,,which, you know, it's not exactly 12 grams
Dialogue: 0,0:10:16.74,0:10:21.21,Default,,0000,0000,0000,,because there are other\Nisotopes, it'll be 12.01 grams.
Dialogue: 0,0:10:21.21,0:10:24.12,Default,,0000,0000,0000,,You see what I mean? A mole\Nis a conversion factor.
Dialogue: 0,0:10:24.12,0:10:28.89,Default,,0000,0000,0000,,Take one mole of anything,\Nit'll be this number in grams.
Dialogue: 0,0:10:28.89,0:10:31.89,Default,,0000,0000,0000,,And so now we can try and\Nanswer our original question.
Dialogue: 0,0:10:31.89,0:10:35.46,Default,,0000,0000,0000,,We asked ourselves, if you\Nhave 3.21 grams of sulfur,
Dialogue: 0,0:10:35.46,0:10:37.02,Default,,0000,0000,0000,,how many atoms there are?
Dialogue: 0,0:10:37.02,0:10:38.22,Default,,0000,0000,0000,,Why don't you pause the video
Dialogue: 0,0:10:38.22,0:10:41.52,Default,,0000,0000,0000,,and see if you can now answer\Nthis question yourself.
Dialogue: 0,0:10:41.52,0:10:43.26,Default,,0000,0000,0000,,If I take one mole of sulfur,
Dialogue: 0,0:10:43.26,0:10:46.65,Default,,0000,0000,0000,,if I take Avogadro number of sulfur atoms,
Dialogue: 0,0:10:46.65,0:10:51.57,Default,,0000,0000,0000,,it'll have a mass of 32.1\Ngrams, roughly 32.1 grams.
Dialogue: 0,0:10:51.57,0:10:54.78,Default,,0000,0000,0000,,So 32.1 grams represents\None mole of sulfur.
Dialogue: 0,0:10:54.78,0:10:56.04,Default,,0000,0000,0000,,But how much sulfur do I have?
Dialogue: 0,0:10:56.04,0:10:59.19,Default,,0000,0000,0000,,I have not 32.1, I have 3.21 grams,
Dialogue: 0,0:10:59.19,0:11:02.33,Default,,0000,0000,0000,,which is just 1/10 of a mole.
Dialogue: 0,0:11:02.33,0:11:05.22,Default,,0000,0000,0000,,That's why I took 3.21 to just\Nkeep the calculation simpler.
Dialogue: 0,0:11:05.22,0:11:07.59,Default,,0000,0000,0000,,We can do it in our head.\NThis is 1/10 of a mole.
Dialogue: 0,0:11:07.59,0:11:09.36,Default,,0000,0000,0000,,So how many atoms you must be having?
Dialogue: 0,0:11:09.36,0:11:13.68,Default,,0000,0000,0000,,1/10 of a mole, so 1/10\Nof the Avogadro number.
Dialogue: 0,0:11:13.68,0:11:16.02,Default,,0000,0000,0000,,So the answer would be\Nthe Avogadro number,
Dialogue: 0,0:11:16.02,0:11:18.54,Default,,0000,0000,0000,,which is 6.02 times 10 to the power 23
Dialogue: 0,0:11:18.54,0:11:20.16,Default,,0000,0000,0000,,divided by 10, 1/10 of it.
Dialogue: 0,0:11:20.16,0:11:23.28,Default,,0000,0000,0000,,So it'll be 6.02 times 10 to the power 22.
Dialogue: 0,0:11:24.18,0:11:25.65,Default,,0000,0000,0000,,Okay, here's our final question.
Dialogue: 0,0:11:25.65,0:11:27.80,Default,,0000,0000,0000,,If I take one mole of carbon dioxide,
Dialogue: 0,0:11:27.80,0:11:29.55,Default,,0000,0000,0000,,what do you think will its mass be?
Dialogue: 0,0:11:29.55,0:11:33.03,Default,,0000,0000,0000,,What is the molar mass of\None mole of carbon dioxide?
Dialogue: 0,0:11:33.03,0:11:36.24,Default,,0000,0000,0000,,Can you pause the video and\Ntry to think about this?
Dialogue: 0,0:11:37.50,0:11:39.30,Default,,0000,0000,0000,,Okay, let's do this step by step.
Dialogue: 0,0:11:39.30,0:11:42.00,Default,,0000,0000,0000,,I know if I have one\Nmole of carbon dioxide,
Dialogue: 0,0:11:42.00,0:11:47.00,Default,,0000,0000,0000,,then it must be having an\NAvogadro number of molecules
Dialogue: 0,0:11:47.07,0:11:48.96,Default,,0000,0000,0000,,of carbon dioxide, right?
Dialogue: 0,0:11:48.96,0:11:51.66,Default,,0000,0000,0000,,Remember, if I had half a mole\Nof carbon dioxide, it means
Dialogue: 0,0:11:51.66,0:11:54.09,Default,,0000,0000,0000,,that I would have half the Avogadro number
Dialogue: 0,0:11:54.09,0:11:55.11,Default,,0000,0000,0000,,of carbon dioxide.
Dialogue: 0,0:11:55.11,0:11:56.10,Default,,0000,0000,0000,,Makes sense, right? Okay.
Dialogue: 0,0:11:56.10,0:11:57.84,Default,,0000,0000,0000,,Anyways, now comes the question
Dialogue: 0,0:11:57.84,0:11:59.64,Default,,0000,0000,0000,,how many carbon atoms must be there
Dialogue: 0,0:11:59.64,0:12:01.17,Default,,0000,0000,0000,,and how many oxygen atoms must be there?
Dialogue: 0,0:12:01.17,0:12:02.07,Default,,0000,0000,0000,,What do you think?
Dialogue: 0,0:12:03.00,0:12:05.52,Default,,0000,0000,0000,,Well, a single carbon dioxide molecule
Dialogue: 0,0:12:05.52,0:12:07.44,Default,,0000,0000,0000,,has one atom of carbon.
Dialogue: 0,0:12:07.44,0:12:10.86,Default,,0000,0000,0000,,If I have five molecules\Nof carbon dioxide,
Dialogue: 0,0:12:10.86,0:12:13.26,Default,,0000,0000,0000,,I have five carbon atoms,
Dialogue: 0,0:12:13.26,0:12:14.79,Default,,0000,0000,0000,,which means if I have these many molecules
Dialogue: 0,0:12:14.79,0:12:18.21,Default,,0000,0000,0000,,of carbon dioxide, I should\Nhave exactly that many amount
Dialogue: 0,0:12:18.21,0:12:20.91,Default,,0000,0000,0000,,of carbon atoms, meaning I have one mole
Dialogue: 0,0:12:20.91,0:12:22.44,Default,,0000,0000,0000,,of carbon atoms with me.
Dialogue: 0,0:12:22.44,0:12:25.29,Default,,0000,0000,0000,,Okay, what about the\Nnumber of oxygen atoms?
Dialogue: 0,0:12:25.29,0:12:30.29,Default,,0000,0000,0000,,Well, each carbon dioxide\Nmolecule has atoms of oxygen.
Dialogue: 0,0:12:30.48,0:12:33.12,Default,,0000,0000,0000,,And so if I had five,\Nfor example, molecules
Dialogue: 0,0:12:33.12,0:12:36.18,Default,,0000,0000,0000,,of carbon dioxide, I would\Nhave twice the amount,
Dialogue: 0,0:12:36.18,0:12:38.22,Default,,0000,0000,0000,,10 atoms of oxygen.
Dialogue: 0,0:12:38.22,0:12:40.47,Default,,0000,0000,0000,,And therefore, if I have\Nthese many molecules
Dialogue: 0,0:12:40.47,0:12:43.53,Default,,0000,0000,0000,,of carbon dioxide, I would\Nhave twice the amount,
Dialogue: 0,0:12:44.79,0:12:48.81,Default,,0000,0000,0000,,which means I have two moles\Nof oxygen atoms with me.
Dialogue: 0,0:12:48.81,0:12:50.40,Default,,0000,0000,0000,,And I can now look at the periodic table
Dialogue: 0,0:12:50.40,0:12:52.95,Default,,0000,0000,0000,,to find the mass of one mole of carbon.
Dialogue: 0,0:12:52.95,0:12:57.42,Default,,0000,0000,0000,,It's 12.0107 grams,
Dialogue: 0,0:12:57.42,0:12:58.56,Default,,0000,0000,0000,,and for oxygen,
Dialogue: 0,0:12:58.56,0:13:02.49,Default,,0000,0000,0000,,it would be 15.9994 grams.
Dialogue: 0,0:13:02.49,0:13:04.44,Default,,0000,0000,0000,,That would be the mass\Nof one mole of oxygen.
Dialogue: 0,0:13:04.44,0:13:06.30,Default,,0000,0000,0000,,But then we have to multiply it by two
Dialogue: 0,0:13:06.30,0:13:08.34,Default,,0000,0000,0000,,because over here, we have two moles.
Dialogue: 0,0:13:08.34,0:13:11.61,Default,,0000,0000,0000,,Simplifying this will\Ngive me the molar mass
Dialogue: 0,0:13:11.61,0:13:12.87,Default,,0000,0000,0000,,of carbon dioxide.
Dialogue: 0,0:13:12.87,0:13:16.68,Default,,0000,0000,0000,,So one mole of carbon dioxide\Nwill have this much mass.
Dialogue: 0,0:13:16.68,0:13:18.84,Default,,0000,0000,0000,,Or we can also say that\Ncarbon dioxide has a mass
Dialogue: 0,0:13:18.84,0:13:23.16,Default,,0000,0000,0000,,of 44.0095 grams per mole.
Dialogue: 0,0:13:23.16,0:13:24.93,Default,,0000,0000,0000,,Same thing. It's the same thing, okay?
Dialogue: 0,0:13:24.93,0:13:26.52,Default,,0000,0000,0000,,They all mean the same thing.
Dialogue: 0,0:13:26.52,0:13:27.51,Default,,0000,0000,0000,,Of course, we can round it off
Dialogue: 0,0:13:27.51,0:13:29.41,Default,,0000,0000,0000,,and we are actually doing a numerical.