The Decolorization of Crystal Violet - Free Educational videos for Students in K-12

The Decolorization of Crystal Violet - By MITK12Videos

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00:10	So we're going to discuss the D . Colorization of
00:12	crystal violet . But first maybe we should talk about
00:15	what crystal violet is exactly . It's a chemical that
00:19	appears to be a dark greenish yellow powder . But
00:23	when we mix it with water it turns into a
00:25	vibrant violet solution . And at the molecular level ,
00:28	the crystal violet molecule looks like this . The red
00:31	dots in the structure represent the electrons that formed the
00:34	chemical bonds . There are also some hydrogen atoms in
00:38	the molecule , but they aren't shown here because it
00:40	would get very crowded . And we can see that
00:43	the more crystal violet powder we add to the water
00:46	, the darker the solution becomes . So what is
00:49	it about the crystal violet molecule that makes the solution
00:52	so very very violent . The answer can be found
00:56	in its structure . An interesting aspect of crystal violet
00:59	structure is the fact that its entire structure is in
01:02	resonance . Now you may be asking yourself what is
01:05	resonance , Let's look at a simpler molecule . 1st
01:10	. Benzene , which has six carbon atoms and six
01:13	hydrogen atoms has two resonant structures . It can be
01:17	drawn like this or like this but it doesn't really
01:22	exist in either of these forms . The D localized
01:25	electrons rotate around the benzene ring so quickly that they
01:29	are effectively shared by all the atoms , which creates
01:33	1.5 bonds between carbon atoms instead of alternating single and
01:37	double bonds . If we look back at crystal violet
01:41	, we can draw many residents structures because electrons are
01:44	D localized across the entire molecule . The D localized
01:48	electrons caused crystal violet to absorb light in the visible
01:52	part of the light spectrum . This is why crystal
01:55	violet is colored . But you don't have to take
01:58	my word for it . We can actually measure how
02:01	crystal violet absorbs light in the laboratory using an instrument
02:04	called an ultraviolet visible spectrum odometer . So let's do
02:09	that . First . We have to put some of
02:11	our solution into a cubit . We then place the
02:14	Q . Bet into the holder inside the spectrum odometer
02:18	. Now when we take a measurement of our solution
02:20	, the spectrum odometer will send a beam of light
02:23	through our solution . And whatever wavelength I set For
02:27	this experiment , I have set the wavelength range from
02:30	290 nm to 700 nm . And now we can
02:35	see the data that the spectrum odometer produced . It
02:38	appears that our solution absorbs light over a range of
02:40	colors And the peak absorption is at 590 nm .
02:46	If we overlay the visible spectrum onto our graph ,
02:49	it looks like our solution is absorbing the most light
02:51	in the yellow range . If it's absorbing light in
02:55	the yellow range , why is our solution violet ?
02:59	Well we don't see the color the solution absorbs .
03:03	We see the colors the solution doesn't absorb and generally
03:07	we will see the complementary color of the color of
03:11	the solution absorbs the most and the complementary color of
03:15	yellow is violet . Now that we know why crystal
03:19	violet is violet and how we can measure just how
03:23	violent it is . We're ready to explore how did
03:26	to colorize it . So again , the answer lies
03:29	with its structure . As we discussed before , the
03:32	electrons are moving throughout the entire molecule very quickly .
03:36	However , the electrons are not spread out evenly .
03:40	Since the nitrogen atoms on the outside of the structure
03:43	have a higher electro negativity . They pulled the electrons
03:47	towards them and away from the center carbon atom .
03:50	This leaves the center carbon atom with a slightly more
03:53	positive charge . The positive charge of the central carbon
03:57	can now attract a chemical species that has a negative
04:00	charge . Of course the crystal violet molecule won't react
04:04	with just any species . It has to be a
04:07	reactive species . A chemical species like hydroxide reacts beautifully
04:14	when the hydroxide ion comes close to the central carbon
04:17	atom , they reacted form equivalent bond . When this
04:21	happens , crystal violet no longer has a positive charge
04:25	. Additionally , the new carbon oxygen bond prevents electrons
04:29	removing throughout the structure and residents is now limited to
04:32	the aromatic greens . So the new structure will no
04:35	longer absorb light at 590 nm and it won't produce
04:40	a violet color for us to see . So we
04:42	have successfully to colorized crystal violet . But let's explore
04:47	one last thing . What if we wanted to d
04:50	colorize crystal violet even faster , you could probably imagine
04:54	that the more hydroxide we put into the solution ,
04:58	the faster the hydroxide would find the crystal violet molecule
05:01	and the faster the solution would be d colorized .
05:04	This too can be verified experimentally . So let that
05:08	be our last task here we have four solutions .
05:11	They all have the same amount of crystal violet in
05:13	them but we're going to vary the amount of hydroxide
05:16	we put in them . So let's say the solution
05:18	on the right has X . Amount of hydroxide .
05:22	The next solution will have to X . The next
05:24	will have three ex and the last solution on the
05:27	left will have six X . So now let's see
05:30	how long it takes for the crystal violet two D
05:32	. Colorize . In summary , crystal violet appears violet
06:21	because the residents in the structure allows it to absorb
06:24	light in the visible spectrum . When the crystal violet
06:28	molecule finds a hydroxide ion , they react , the
06:31	residence is disrupted and the crystal violet can no longer
06:35	absorb light in the visible spectrum . Therefore it's be
06:39	colorized .

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