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Journal Week of 8 March 2010 Latest Update: Friday, 12 March 2010 08:21 -0500 |
0:00:00.750,0:00:04.940 I'm Robert response in and this is the home scientist video series 0:00:04.940,0:00:09.540 in this segment will isolate elemental running from a water treatment and nickel sold by 0:00:09.540,0:00:11.959 swimming pool and hot tub suppliers 0:00:11.959,0:00:16.559 the chemicals called for a mean bass which is actually crusading bromide 0:00:16.559,0:00:21.179 it's available and one were to come almost for for five bucks a pound 0:00:21.179,0:00:26.809 like the other hilton's brandon is very corrosive and produces irritating choking hymns 0:00:26.809,0:00:31.009 although it's liquid at room temperature its world war one point behind the profession 0:00:31.009,0:00:34.410 that when we produce his pocket and twist in the papers 0:00:34.410,0:00:38.059 if you use a procedure that's wrong in this movie is obsolete from me 0:00:38.059,0:00:41.320 you don't have to watch your honor if she lost both 0:00:41.320,0:00:46.100 all use the same reaction to isolate brown mean that I used in an earlier video obviously 0:00:46.100,0:00:47.090 I'm going 0:00:47.090,0:00:51.410 the city find a solution that can change your mind on its and reacting the solution with 0:00:51.410,0:00:56.390 a strong marks about your often does is provide arms of nicole brown 0:00:56.390,0:00:58.680 worries it's supposed to 0:00:58.680,0:01:03.820 okay let's get started the more massive said he and brown modest wanted to point eight 0:01:03.820,0:01:05.660 nine four grams jamal 0:01:05.660,0:01:10.860 i'd wait out five point one five grams of sodium bromide which is about zero point zero 0:01:10.860,0:01:12.120 five miles 0:01:12.120,0:01:16.870 so to my mind is seventy seven point six six percent browning by mass 0:01:16.870,0:01:21.370 so are expected you live from maine is four points here in France 0:01:21.370,0:01:25.810 so do you bring to mind is extremely soluble in water so I actually need only about six 0:01:25.810,0:01:28.900 or seven milliliters to dissolve blood sample 0:01:28.900,0:01:35.900 on Monday and would then because as we've seen excess water isn't a problem 0:01:41.550,0:01:46.670 the city in Vermont is all the next step is to and a strong alliances 0:01:46.670,0:01:51.299 I'm using hundred court yesterday you can also use or cure cancer there were any other 0:01:51.299,0:01:54.430 strong allies 0:01:54.430,0:01:58.820 the next step is to authorize the Vermont on students over me 0:01:58.820,0:02:03.460 you can use almost any star marks allows you to do that including Korean wonderfully or 0:02:03.460,0:02:05.150 vast improvement in it 0:02:05.150,0:02:09.640 I'm using ordinary folks were three percent hydrogen peroxide because it's a very strong 0:02:09.640,0:02:12.959 talks about you that we have stood for what we ought to do more 0:02:12.959,0:02:18.379 I mean at least zero four zero five ml of hydrogen peroxide thoughts about solving bromide 0:02:18.379,0:02:20.439 on staten island in a brilliant 0:02:20.439,0:02:25.939 most or cross on solution is about zero point eight more for about zero point zero zero 0:02:25.939,0:02:28.139 zero eight most per milliliter 0:02:28.139,0:02:30.640 so I mean about sixty two and a half milliliters 0:02:30.640,0:02:37.640 I'm actually use in about seventy five the leaders to make sure the prosecution access 0:02:55.609,0:02:58.729 for the first few seconds nothing appears to happen 0:02:58.729,0:03:00.589 as the reaction proceedings 0:03:00.589,0:03:06.339 the solution is since a gradually beeper yellow color as the bottom line on chirac's about 0:03:06.339,0:03:07.529 elemental them 0:03:07.529,0:03:14.529 so will allow this to sit the reaction to continue to completion 0:03:14.589,0:03:18.729 okay it's been a couple hours and the results on what I expected 0:03:18.729,0:03:22.679 the solution in the flask is now a fairly intense yellow orange color which indicates 0:03:22.679,0:03:27.819 that there's some brownie President but not nearly as much as expected frankly when I 0:03:27.819,0:03:31.329 added the hydrogen peroxide unexpectedly is also more 0:03:31.329,0:03:35.909 to what occurred when I had of the hydrogen peroxide the I've got a mixture of the earlier 0:03:35.909,0:03:36.880 video 0:03:36.880,0:03:41.890 there's with the %uh relatively instantaneous transformation of the ground what our would 0:03:41.890,0:03:42.809 around me 0:03:42.809,0:03:46.180 well clearly that's marker we do have some brown denied before 0:03:46.180,0:03:48.619 last week what's giving it the orange color 0:03:48.619,0:03:52.499 but nowhere near as much as expected 0:03:52.499,0:03:57.659 well as it turned out I didn't end up with a concentrated on the more I was expecting 0:03:57.659,0:04:01.439 instead I ended up with about one hundred world leaders of relatively donnelly printing 0:04:01.439,0:04:02.239 water 0:04:02.239,0:04:07.430 that work for what I needed it for the first place testing some organics from saturation 0:04:07.430,0:04:10.629 but what happened here raises an important point 0:04:10.629,0:04:14.749 as any practicing cameras will tell you things don't always work out the way you expect them 0:04:14.749,0:04:19.339 to even if you've done the same reaction successfully before 0:04:19.339,0:04:23.809 sometimes nothing at all happens sometimes a lot more happens that what you were expecting 0:04:23.809,0:04:27.289 which is why we always wear gloves and calls in a while 0:04:27.289,0:04:29.279 we subscribe rate and comment | 0:00:00.750,0:00:04.940 I'm Robert Bruce Thompson and this is the Home Scientist video series. 0:00:04.940,0:00:09.540 In this segment we'll isolate elemental bromine from a water-treatment chemical sold by 0:00:09.540,0:00:11.959 swimming pool and hot tub suppliers. 0:00:11.959,0:00:16.559 The chemical is called bromine base, which is actually crude sodium bromide. 0:00:16.559,0:00:21.179 It's available in one- or two-pound bottles for four or five bucks a pound. 0:00:21.179,0:00:26.809 Like the other halogens, bromine is very corrosive and produces irritating and choking fumes. 0:00:26.809,0:00:31.009 Although it's liquid at room temperature its low boiling point and high vapor pressure mean 0:00:31.009,0:00:34.410 it readily produces toxic and corrosive vapors. 0:00:34.410,0:00:38.059 If you use the procedure described in this video to isolate bromine 0:00:38.059,0:00:41.320 do it only outdoors or under an exhaust hood. 0:00:41.320,0:00:46.100 I'll use the same reaction to isolate bromine that I used in an earlier video to isolate 0:00:46.100,0:00:47.090 iodine. 0:00:47.090,0:00:51.410 Acidifying a solution that contains bromide ions and reacting the solution with 0:00:51.410,0:00:56.390 a strong oxidizer oxidizes bromide ions to elemental bromine. 0:00:56.390,0:00:58.680 Or at least it's supposed to. 0:00:58.680,0:01:03.820 Okay, let's get started. The molar mass of sodium bromide is 102.894 0:01:03.820,0:01:05.660 grams per mole. 0:01:05.660,0:01:10.860 I've weighed out 5.15 grams of sodium bromide, which is about 0:01:10.860,0:01:12.120 0.05 moles. 0:01:12.120,0:01:16.870 Sodium bromide is 77.66 percent bromine by mass, 0:01:16.870,0:01:21.370 so our expected yield of bromine is 4.0 grams. 0:01:21.370,0:01:25.810 Sodium bromide is extremely soluble in water so I actually need only about six 0:01:25.810,0:01:28.900 or seven milliliters to dissolve my sample. 0:01:28.900,0:01:35.900 I'm going to add more than that because, as we'll see, excess water isn't a problem. 0:01:41.550,0:01:46.670 With the sodium bromide dissolved, the next step is to add a strong mineral acid. 0:01:46.670,0:01:51.299 I'm using hydrochloric acid, but you can also use sulfuric acid or any other 0:01:51.299,0:01:54.430 strong mineral acid. 0:01:54.430,0:01:58.820 The next step is to oxidize the bromide ions to elemental bromine. 0:01:58.820,0:02:03.460 You can use almost any strong oxidizer to do that including chlorine laundry bleach 0:02:03.460,0:02:05.150 potassium permanganate. 0:02:05.150,0:02:09.640 I'm using ordinary drugstore three percent hydrogen peroxide because it's a very strong 0:02:09.640,0:02:12.959 oxidizer that reacts to form only oxygen and water. 0:02:12.959,0:02:18.379 I need at least 0.05 moles of hydrogen peroxide to oxidize all of the bromide 0:02:18.379,0:02:20.439 ions to elemental bromine. 0:02:20.439,0:02:25.939 Drugstore peroxide solution is about 0.8 molar, or about 0.0008 0:02:25.939,0:02:28.139 moles per milliliter, 0:02:28.139,0:02:30.640 so I need about 62.5 milliliters. 0:02:30.640,0:02:37.640 I'm actually using about 75 milliliters to make sure the peroxide is in excess. 0:02:55.609,0:02:58.729 For the first few seconds nothing appears to happen. 0:02:58.729,0:03:00.589 As the reaction proceeds 0:03:00.589,0:03:06.339 the solution assumes a gradually deeper yellow color as the bromide ions are oxidized 0:03:06.339,0:03:07.529 to elemental bromine. 0:03:07.529,0:03:14.529 So, we'll allow this to sit for the reaction to continue to completion. 0:03:14.589,0:03:18.729 Okay, it's been a couple hours and the results aren't what I expected. 0:03:18.729,0:03:22.679 The solution in the flask is now a fairly intense yellow orange color which indicates 0:03:22.679,0:03:27.819 that there's some bromine present, but not nearly as much as expected. Frankly, when I 0:03:27.819,0:03:31.329 added the hydrogen peroxide, I expected results similar 0:03:31.329,0:03:35.909 to what occurred when I added the hydrogen peroxide to the iodide mixture in the earlier 0:03:35.909,0:03:36.880 video. 0:03:36.880,0:03:41.890 That is, for the, uh, relatively instantaneous transformation of the bromide ion to 0:03:41.890,0:03:42.809 liquid bromine. 0:03:42.809,0:03:46.180 Uh, clearly that's not occurred. We do have some bromine in the flask 0:03:46.180,0:03:48.619 which is what's giving it the orange color 0:03:48.619,0:03:52.499 but nowhere near as much as I expected. 0:03:52.499,0:03:57.659 Well, as it turned out I didn't end up with the concentrated bromine water I was expecting. 0:03:57.659,0:04:01.439 Instead I ended up with about 100 milliliters of relatively dilute bromine 0:04:01.439,0:04:02.239 water. 0:04:02.239,0:04:07.430 That worked for what I needed it for in the first place, testing some organics for unsaturation, 0:04:07.430,0:04:10.629 but what happened here raises an important point. 0:04:10.629,0:04:14.749 As any practicing chemist will tell you, things don't always work out the way you expect them 0:04:14.749,0:04:19.339 to, even if you've done the same reaction successfully before. 0:04:19.339,0:04:23.809 Sometimes nothing at all happens. Sometimes a lot more happens than what you were expecting, 0:04:23.809,0:04:27.289 which is why we always wear gloves and goggles in the lab. 0:04:27.289,0:04:29.279 Please subscribe, rate, and comment. |