[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.29,0:00:01.62,Default,,0000,0000,0000,,- [Instructor] So let's\Nsay that I have a vial
Dialogue: 0,0:00:01.62,0:00:03.84,Default,,0000,0000,0000,,of some mystery liquid right over here,
Dialogue: 0,0:00:03.84,0:00:06.08,Default,,0000,0000,0000,,and I want to start figuring\Nout what's going on there.
Dialogue: 0,0:00:06.08,0:00:08.07,Default,,0000,0000,0000,,And the first step is to think about,
Dialogue: 0,0:00:08.07,0:00:09.73,Default,,0000,0000,0000,,is it just one substance
Dialogue: 0,0:00:09.73,0:00:12.21,Default,,0000,0000,0000,,or is it a mixture of multiple substances?
Dialogue: 0,0:00:12.21,0:00:15.23,Default,,0000,0000,0000,,And the focus of this video is a technique
Dialogue: 0,0:00:15.23,0:00:17.54,Default,,0000,0000,0000,,to separate out the substances
Dialogue: 0,0:00:17.54,0:00:19.86,Default,,0000,0000,0000,,to understand at least how many there are,
Dialogue: 0,0:00:19.86,0:00:23.03,Default,,0000,0000,0000,,and this technique generally\Nis called chromatography,
Dialogue: 0,0:00:23.03,0:00:25.68,Default,,0000,0000,0000,,but we'll focus on thin\Nlayer chromatography
Dialogue: 0,0:00:25.68,0:00:27.57,Default,,0000,0000,0000,,which is the most common\Nthat you might see,
Dialogue: 0,0:00:27.57,0:00:29.59,Default,,0000,0000,0000,,but other variations of chromatography
Dialogue: 0,0:00:29.59,0:00:31.15,Default,,0000,0000,0000,,like paper chromatography
Dialogue: 0,0:00:31.15,0:00:33.89,Default,,0000,0000,0000,,operate on very similar principles.
Dialogue: 0,0:00:33.89,0:00:37.78,Default,,0000,0000,0000,,So what we're going to do is set up
Dialogue: 0,0:00:37.78,0:00:40.79,Default,,0000,0000,0000,,on top of something like glass or plastic,
Dialogue: 0,0:00:40.79,0:00:45.79,Default,,0000,0000,0000,,we're going to put a thin layer\Nof a solid polar substance.
Dialogue: 0,0:00:46.80,0:00:48.04,Default,,0000,0000,0000,,Now, what you typically do
Dialogue: 0,0:00:48.04,0:00:50.65,Default,,0000,0000,0000,,is put a thin layer of silica gel,
Dialogue: 0,0:00:50.65,0:00:55.14,Default,,0000,0000,0000,,that's the most common solid\Npolar substance that folks use.
Dialogue: 0,0:00:55.14,0:00:56.43,Default,,0000,0000,0000,,And it's also porous.
Dialogue: 0,0:00:56.43,0:00:58.50,Default,,0000,0000,0000,,And the fact that it's\Nporous is really important
Dialogue: 0,0:00:58.50,0:01:01.29,Default,,0000,0000,0000,,because we're going to want\Nliquid to have capillary action
Dialogue: 0,0:01:01.29,0:01:03.48,Default,,0000,0000,0000,,and travel up through it.
Dialogue: 0,0:01:03.48,0:01:05.60,Default,,0000,0000,0000,,Now, the silica gel, as I mentioned,
Dialogue: 0,0:01:05.60,0:01:08.98,Default,,0000,0000,0000,,this thing is very polar.
Dialogue: 0,0:01:10.44,0:01:11.27,Default,,0000,0000,0000,,Now, what we're going to do
Dialogue: 0,0:01:11.27,0:01:12.97,Default,,0000,0000,0000,,is take some of our mystery substance,
Dialogue: 0,0:01:12.97,0:01:14.90,Default,,0000,0000,0000,,let's say it's this color right over here,
Dialogue: 0,0:01:14.90,0:01:19.90,Default,,0000,0000,0000,,and we're going to place a\Ndot of it on that silica gel.
Dialogue: 0,0:01:19.94,0:01:21.37,Default,,0000,0000,0000,,You then want to take this plate
Dialogue: 0,0:01:21.37,0:01:23.18,Default,,0000,0000,0000,,that has the silica gel on it
Dialogue: 0,0:01:23.18,0:01:25.67,Default,,0000,0000,0000,,and that little dot of\Nour mystery substance,
Dialogue: 0,0:01:25.67,0:01:30.06,Default,,0000,0000,0000,,and then you want to dip just\None end of it in a solution.
Dialogue: 0,0:01:30.06,0:01:31.08,Default,,0000,0000,0000,,And what's really important is that
Dialogue: 0,0:01:31.08,0:01:35.12,Default,,0000,0000,0000,,the solution is less\Npolar than the silica gel.
Dialogue: 0,0:01:35.12,0:01:37.43,Default,,0000,0000,0000,,Less polar here.
Dialogue: 0,0:01:37.43,0:01:39.62,Default,,0000,0000,0000,,And we'll talk a little\Nbit about what happens
Dialogue: 0,0:01:39.62,0:01:41.60,Default,,0000,0000,0000,,depending on how polar this is.
Dialogue: 0,0:01:41.60,0:01:44.81,Default,,0000,0000,0000,,Now, usually this is going\Nto be a very shallow amount
Dialogue: 0,0:01:44.81,0:01:47.53,Default,,0000,0000,0000,,of this solution, which, as we'll see,
Dialogue: 0,0:01:47.53,0:01:49.36,Default,,0000,0000,0000,,will be something of a solvent.
Dialogue: 0,0:01:49.36,0:01:51.94,Default,,0000,0000,0000,,And you usually want to put\Nit in a closed container
Dialogue: 0,0:01:51.94,0:01:52.77,Default,,0000,0000,0000,,like this
Dialogue: 0,0:01:52.77,0:01:55.98,Default,,0000,0000,0000,,so that this fluid down\Nhere doesn't evaporate out.
Dialogue: 0,0:01:55.98,0:01:58.16,Default,,0000,0000,0000,,And then what do you\Nthink is going to happen?
Dialogue: 0,0:01:58.16,0:02:00.97,Default,,0000,0000,0000,,Well, as I mentioned, this\Nis a porous substance here.
Dialogue: 0,0:02:00.97,0:02:03.16,Default,,0000,0000,0000,,And so you're going to\Nhave capillary action.
Dialogue: 0,0:02:03.16,0:02:05.96,Default,,0000,0000,0000,,This fluid at the bottom\Nis going to move upwards
Dialogue: 0,0:02:05.96,0:02:07.26,Default,,0000,0000,0000,,through the silica gel,
Dialogue: 0,0:02:07.26,0:02:09.32,Default,,0000,0000,0000,,through those little\Npores in the silica gel.
Dialogue: 0,0:02:09.32,0:02:11.57,Default,,0000,0000,0000,,This is the stationary phase.\NWhy do we call it that?
Dialogue: 0,0:02:11.57,0:02:12.67,Default,,0000,0000,0000,,Well, 'cause it's not moving.
Dialogue: 0,0:02:12.67,0:02:16.27,Default,,0000,0000,0000,,And you can imagine we would\Ncall this less polar solvent
Dialogue: 0,0:02:17.17,0:02:18.61,Default,,0000,0000,0000,,the mobile phase,
Dialogue: 0,0:02:18.61,0:02:21.97,Default,,0000,0000,0000,,because that is traveling\Nthrough the silica gel
Dialogue: 0,0:02:21.97,0:02:25.01,Default,,0000,0000,0000,,and it's picking up some\Nof this mystery substance
Dialogue: 0,0:02:25.01,0:02:26.70,Default,,0000,0000,0000,,and it's transporting it.
Dialogue: 0,0:02:26.70,0:02:28.28,Default,,0000,0000,0000,,And let's say this mystery substance
Dialogue: 0,0:02:28.28,0:02:30.61,Default,,0000,0000,0000,,is made up of two different things.
Dialogue: 0,0:02:30.61,0:02:33.20,Default,,0000,0000,0000,,If something is more polar,
Dialogue: 0,0:02:33.20,0:02:35.21,Default,,0000,0000,0000,,that means it's going to be more attracted
Dialogue: 0,0:02:35.21,0:02:37.60,Default,,0000,0000,0000,,to the stationary phase\Nwhich is very polar.
Dialogue: 0,0:02:37.60,0:02:40.49,Default,,0000,0000,0000,,And so it's not going to travel that far,
Dialogue: 0,0:02:40.49,0:02:42.21,Default,,0000,0000,0000,,while the parts of our mystery substance
Dialogue: 0,0:02:42.21,0:02:43.45,Default,,0000,0000,0000,,that are less polar,
Dialogue: 0,0:02:43.45,0:02:46.50,Default,,0000,0000,0000,,they're not going to be attracted\Nto the silica gel as much.
Dialogue: 0,0:02:46.50,0:02:49.41,Default,,0000,0000,0000,,So they're going to travel\Nfurther with the solvent.
Dialogue: 0,0:02:49.41,0:02:51.91,Default,,0000,0000,0000,,So maybe it might go like that.
Dialogue: 0,0:02:51.91,0:02:53.53,Default,,0000,0000,0000,,And you would run this\Nuntil your mobile phase
Dialogue: 0,0:02:53.53,0:02:56.94,Default,,0000,0000,0000,,makes a good way to the\Ntop of your silica gel
Dialogue: 0,0:02:56.94,0:02:58.19,Default,,0000,0000,0000,,right over here.
Dialogue: 0,0:02:58.19,0:02:59.38,Default,,0000,0000,0000,,Now, just looking at this,
Dialogue: 0,0:02:59.38,0:03:01.16,Default,,0000,0000,0000,,and the reason why it was\Ncalled chromatography is
Dialogue: 0,0:03:01.16,0:03:02.28,Default,,0000,0000,0000,,when they originally did this,
Dialogue: 0,0:03:02.28,0:03:04.76,Default,,0000,0000,0000,,they were actually separating\Nout various tissues
Dialogue: 0,0:03:04.76,0:03:07.61,Default,,0000,0000,0000,,in vegetation that had different colors.
Dialogue: 0,0:03:07.61,0:03:10.16,Default,,0000,0000,0000,,The chroma is referring\Nto the various colors,
Dialogue: 0,0:03:10.16,0:03:11.96,Default,,0000,0000,0000,,but it doesn't necessarily\Neven have to refer to things
Dialogue: 0,0:03:11.96,0:03:13.04,Default,,0000,0000,0000,,that have different colors
Dialogue: 0,0:03:13.04,0:03:15.63,Default,,0000,0000,0000,,or sometimes you might need\Na UV light to see them.
Dialogue: 0,0:03:15.63,0:03:17.44,Default,,0000,0000,0000,,But when you run thin\Nlayer chromatography,
Dialogue: 0,0:03:17.44,0:03:20.78,Default,,0000,0000,0000,,you will see that your\Noriginal dot will have traveled
Dialogue: 0,0:03:20.78,0:03:22.66,Default,,0000,0000,0000,,to various degrees with your solvent
Dialogue: 0,0:03:22.66,0:03:24.86,Default,,0000,0000,0000,,and then will now be multiple dots
Dialogue: 0,0:03:24.86,0:03:28.52,Default,,0000,0000,0000,,depending on how many things\Nwere in your original mixture.
Dialogue: 0,0:03:28.52,0:03:31.67,Default,,0000,0000,0000,,And as I just mentioned,\Nthis thing right over here,
Dialogue: 0,0:03:31.67,0:03:35.52,Default,,0000,0000,0000,,this is the less polar thing\Nis going to travel further
Dialogue: 0,0:03:35.52,0:03:40.38,Default,,0000,0000,0000,,than the more polar thing, more\Npolar constituent substance,
Dialogue: 0,0:03:40.38,0:03:42.85,Default,,0000,0000,0000,,because the more polar\Nthing is more attractive
Dialogue: 0,0:03:42.85,0:03:45.57,Default,,0000,0000,0000,,to the silica gel, which is stationary,
Dialogue: 0,0:03:45.57,0:03:49.44,Default,,0000,0000,0000,,and there is a way to quantify\Nhow far these things traveled
Dialogue: 0,0:03:49.44,0:03:51.66,Default,,0000,0000,0000,,relative to your solvent.
Dialogue: 0,0:03:51.66,0:03:54.70,Default,,0000,0000,0000,,And that's called a retention factor.
Dialogue: 0,0:03:54.70,0:03:57.85,Default,,0000,0000,0000,,Retention factor.
Dialogue: 0,0:03:59.01,0:04:02.78,Default,,0000,0000,0000,,Which the shorthand is R subscript f.
Dialogue: 0,0:04:02.78,0:04:07.20,Default,,0000,0000,0000,,And it's just defined\Nas the distance traveled
Dialogue: 0,0:04:08.17,0:04:13.17,Default,,0000,0000,0000,,by the solute divided\Nby the distance traveled
Dialogue: 0,0:04:18.69,0:04:22.08,Default,,0000,0000,0000,,by the solvent.
Dialogue: 0,0:04:22.08,0:04:23.09,Default,,0000,0000,0000,,And we need to be clear.
Dialogue: 0,0:04:23.09,0:04:26.00,Default,,0000,0000,0000,,It's not the distance traveled\Nby the solvent in total,
Dialogue: 0,0:04:26.00,0:04:29.81,Default,,0000,0000,0000,,it's the distance traveled by\Nthe solvent from this origin,
Dialogue: 0,0:04:29.81,0:04:32.75,Default,,0000,0000,0000,,from where we applied\Nthis dot right over here.
Dialogue: 0,0:04:32.75,0:04:36.35,Default,,0000,0000,0000,,So, past the origin.
Dialogue: 0,0:04:37.32,0:04:39.89,Default,,0000,0000,0000,,And let me label that as the origin.
Dialogue: 0,0:04:40.73,0:04:42.73,Default,,0000,0000,0000,,So what would it be in this situation?
Dialogue: 0,0:04:42.73,0:04:46.93,Default,,0000,0000,0000,,Well, to help us there, we\Nwould have to get out a ruler.
Dialogue: 0,0:04:46.93,0:04:51.93,Default,,0000,0000,0000,,So the retention factor for\Nsubstance A right over here,
Dialogue: 0,0:04:52.40,0:04:54.89,Default,,0000,0000,0000,,so I'll put that dot there, label that A,
Dialogue: 0,0:04:54.89,0:04:58.56,Default,,0000,0000,0000,,would be equal to the distance\Ntraveled by the solute,
Dialogue: 0,0:04:58.56,0:05:03.34,Default,,0000,0000,0000,,which we can see, it\Ntraveled one centimeter,
Dialogue: 0,0:05:03.34,0:05:05.04,Default,,0000,0000,0000,,one centimeter,
Dialogue: 0,0:05:05.04,0:05:09.11,Default,,0000,0000,0000,,over the distance traveled by\Nthe solvent past the origin.
Dialogue: 0,0:05:09.11,0:05:11.81,Default,,0000,0000,0000,,And so that is going to be,
Dialogue: 0,0:05:11.81,0:05:15.11,Default,,0000,0000,0000,,we see it traveled five\Ncentimeters past the origin.
Dialogue: 0,0:05:15.11,0:05:17.81,Default,,0000,0000,0000,,So one centimeter over five centimeters,
Dialogue: 0,0:05:17.81,0:05:19.81,Default,,0000,0000,0000,,which is the same thing as 0.2.
Dialogue: 0,0:05:20.70,0:05:24.63,Default,,0000,0000,0000,,And then the retention\Nfactor for substance B
Dialogue: 0,0:05:26.19,0:05:29.75,Default,,0000,0000,0000,,is going to be equal to,\Nhow far did it travel?
Dialogue: 0,0:05:29.75,0:05:31.85,Default,,0000,0000,0000,,Well, it traveled three centimeters
Dialogue: 0,0:05:33.30,0:05:36.48,Default,,0000,0000,0000,,out of a total of five\Ncentimeters for the solvent,
Dialogue: 0,0:05:36.48,0:05:37.82,Default,,0000,0000,0000,,past this origin,
Dialogue: 0,0:05:37.82,0:05:40.47,Default,,0000,0000,0000,,past where we put the\Nsample right over there.
Dialogue: 0,0:05:40.47,0:05:45.41,Default,,0000,0000,0000,,Five centimeters, which is equal to 0.6.
Dialogue: 0,0:05:45.41,0:05:47.24,Default,,0000,0000,0000,,So notice, in this situation,
Dialogue: 0,0:05:47.24,0:05:50.66,Default,,0000,0000,0000,,the more polar substance\Nhad a lower retention factor
Dialogue: 0,0:05:50.66,0:05:54.55,Default,,0000,0000,0000,,than the less polar substance,\Nand that makes sense.
Dialogue: 0,0:05:54.55,0:05:59.49,Default,,0000,0000,0000,,Because our stationary phase\Nis more polar than our solvent,
Dialogue: 0,0:05:59.49,0:06:03.50,Default,,0000,0000,0000,,and so the things that are\Nmore polar were harder to move
Dialogue: 0,0:06:03.50,0:06:06.25,Default,,0000,0000,0000,,by the less polar solvent.