1 00:00:00,500 --> 00:00:05,953 [SQUEAKING] [RUSTLING] [CLICKING] 2 00:00:05,953 --> 00:00:07,370 VIVIAN SONG: In this video, I will 3 00:00:07,370 --> 00:00:10,850 be going over Goodie Bag number eight, which is about reactions 4 00:00:10,850 --> 00:00:12,350 and reaction rates. 5 00:00:12,350 --> 00:00:17,240 What you'll need are pH strips, small measuring cups, stirrers, 6 00:00:17,240 --> 00:00:22,220 gloves, citric powder, cups, a scale, and seashells. 7 00:00:22,220 --> 00:00:25,790 No sea animals were harmed in the making of this Goodie bag. 8 00:00:25,790 --> 00:00:28,880 The objectives are to understand how climate change has 9 00:00:28,880 --> 00:00:30,950 caused ocean acidification. 10 00:00:30,950 --> 00:00:34,040 Assess the order of the reaction from empirical data. 11 00:00:34,040 --> 00:00:37,190 Learn how temperature can affect the reaction rate. 12 00:00:37,190 --> 00:00:40,520 And measure the pH of a reaction using pH strips. 13 00:00:40,520 --> 00:00:43,040 Some conceptual questions to think about 14 00:00:43,040 --> 00:00:44,900 are, what is the reaction order? 15 00:00:44,900 --> 00:00:46,610 And how does the reaction rate change 16 00:00:46,610 --> 00:00:51,720 if the temperature increases or if we have outside pH effects? 17 00:00:51,720 --> 00:00:55,160 Now, in this Goodie bag, we will be exploring the application 18 00:00:55,160 --> 00:00:57,830 of reaction rates in ocean acidification 19 00:00:57,830 --> 00:00:59,480 due to climate change and what that 20 00:00:59,480 --> 00:01:01,370 means for many sea animals. 21 00:01:01,370 --> 00:01:03,080 As you can see from this graph, there 22 00:01:03,080 --> 00:01:06,650 is a strong positive correlation between increasing carbon 23 00:01:06,650 --> 00:01:08,720 dioxide levels in the atmosphere, which 24 00:01:08,720 --> 00:01:11,360 is marked by the red, and decreasing pH 25 00:01:11,360 --> 00:01:15,170 in the ocean, which corresponds to increasing acidity, as seen 26 00:01:15,170 --> 00:01:16,400 in the green. 27 00:01:16,400 --> 00:01:19,520 What exactly is going on in terms of the chemistry? 28 00:01:19,520 --> 00:01:23,390 First, carbon dioxide from the air dissolves into the oceans 29 00:01:23,390 --> 00:01:26,400 and reacts with water to form carbonic acid. 30 00:01:26,400 --> 00:01:29,330 Then the carbonic acid donates a proton. 31 00:01:29,330 --> 00:01:32,120 Finally, calcium carbonate from seashells 32 00:01:32,120 --> 00:01:34,940 reacts with excess protons in solution 33 00:01:34,940 --> 00:01:36,860 to formed bicarbonate ions. 34 00:01:36,860 --> 00:01:38,210 What does this all mean? 35 00:01:38,210 --> 00:01:41,210 Seashells are dissolving in a more acidic ocean, 36 00:01:41,210 --> 00:01:43,010 which is very sad. 37 00:01:43,010 --> 00:01:44,990 One final note about the slide. 38 00:01:44,990 --> 00:01:47,450 I've only drawn the forward reaction arrows. 39 00:01:47,450 --> 00:01:50,090 But these reactions are actually reversible. 40 00:01:50,090 --> 00:01:52,670 So there should also be backward arrows. 41 00:01:52,670 --> 00:01:54,740 However, the forward reactions are 42 00:01:54,740 --> 00:01:57,180 more dominant to the reverse reactions. 43 00:01:57,180 --> 00:02:00,140 So the net product is that of the forward reaction. 44 00:02:00,140 --> 00:02:02,120 Now, let's dive into the experiment 45 00:02:02,120 --> 00:02:04,700 and see this happen in real life. 46 00:02:04,700 --> 00:02:06,620 First, take out one of your seashells 47 00:02:06,620 --> 00:02:08,490 and weigh it with your scale. 48 00:02:08,490 --> 00:02:11,240 Next, put on your elegant nitrile gloves. 49 00:02:11,240 --> 00:02:14,630 And take a large plastic cup and have it filled with tap water 50 00:02:14,630 --> 00:02:16,070 about halfway. 51 00:02:16,070 --> 00:02:18,530 Measure out two scoops of the citric powder 52 00:02:18,530 --> 00:02:20,840 using the small but accurate measuring cup. 53 00:02:20,840 --> 00:02:22,430 And put it into the water. 54 00:02:22,430 --> 00:02:24,410 Then stir while using the stirrer 55 00:02:24,410 --> 00:02:27,590 until all of the citric powder is fully dissolved. 56 00:02:27,590 --> 00:02:29,060 It might take a minute of stirring, 57 00:02:29,060 --> 00:02:31,190 but the water should look pretty clear. 58 00:02:31,190 --> 00:02:33,150 After that, you can use your pH strip 59 00:02:33,150 --> 00:02:35,360 to measure the pH of the solution. 60 00:02:35,360 --> 00:02:36,500 Have a timer ready. 61 00:02:36,500 --> 00:02:38,480 And when you're ready, place the shells 62 00:02:38,480 --> 00:02:40,580 that you weighed into the low pH solution. 63 00:02:40,580 --> 00:02:42,080 And record what you observe. 64 00:02:42,080 --> 00:02:44,990 After 20 minutes, take out the shells with your gloves 65 00:02:44,990 --> 00:02:47,090 on and record the exact time. 66 00:02:47,090 --> 00:02:49,940 Let the shells dry for maybe half an hour or so so 67 00:02:49,940 --> 00:02:51,710 that all the water has evaporated. 68 00:02:51,710 --> 00:02:53,270 And then measure the weight. 69 00:02:53,270 --> 00:02:55,220 Repeat this step two more times so 70 00:02:55,220 --> 00:02:59,390 that you have data points of the mass of the shell at zero, 20, 71 00:02:59,390 --> 00:03:01,010 and 40 minutes. 72 00:03:01,010 --> 00:03:04,040 The pH that I measured was a pH of 2, 73 00:03:04,040 --> 00:03:07,647 as you can see using this pH tester. 74 00:03:07,647 --> 00:03:09,230 While doing the experiment, you should 75 00:03:09,230 --> 00:03:11,540 see that the sea shells are dissolving 76 00:03:11,540 --> 00:03:12,930 in the acidic solution. 77 00:03:12,930 --> 00:03:17,840 And here, I've captured a hyper-lapse of this happening. 78 00:03:17,840 --> 00:03:20,060 The focus of our experiment is to figure out 79 00:03:20,060 --> 00:03:22,310 the reaction rate of the dissolution of calcium 80 00:03:22,310 --> 00:03:23,030 carbonate. 81 00:03:23,030 --> 00:03:26,090 As a reminder, the reaction rate is equal to some rate 82 00:03:26,090 --> 00:03:29,480 constant times the concentration of the calcium 83 00:03:29,480 --> 00:03:33,800 ions to the n power times the concentration of carbonate ions 84 00:03:33,800 --> 00:03:38,350 to the n power, where n plus n is equal to the reaction order. 85 00:03:38,350 --> 00:03:40,580 And that is determined empirically from the data 86 00:03:40,580 --> 00:03:42,440 that we've gathered. 87 00:03:42,440 --> 00:03:46,190 As you can see from the data, this reaction is 0th order. 88 00:03:46,190 --> 00:03:48,590 I plotted the concentration of carbonate ions 89 00:03:48,590 --> 00:03:50,570 on the y-axis, which you can figure out, 90 00:03:50,570 --> 00:03:53,120 assuming that you poured 0.2 liters of water 91 00:03:53,120 --> 00:03:56,120 in your experiment, and time on the x-axis. 92 00:03:56,120 --> 00:03:59,650 Because this plot looks linear, the rate is constant over time 93 00:03:59,650 --> 00:04:02,420 and does not depend on the concentration of carbonate ions 94 00:04:02,420 --> 00:04:03,770 already in solution. 95 00:04:03,770 --> 00:04:06,350 Thus, this is a 0th order reaction. 96 00:04:06,350 --> 00:04:09,470 You could also imagine the same plot with calcium ions 97 00:04:09,470 --> 00:04:12,740 since we know that the calcium ions and carbonate ions exist 98 00:04:12,740 --> 00:04:15,620 in a one-to-one molarity ratio. 99 00:04:15,620 --> 00:04:17,420 In summary, the reaction rate order 100 00:04:17,420 --> 00:04:18,829 is determined empirically. 101 00:04:18,829 --> 00:04:22,040 And the reaction rate can depend on temperature and pH. 102 00:04:22,040 --> 00:04:25,130 Now, we didn't have time to do this pH and temperature 103 00:04:25,130 --> 00:04:26,980 dependence experiment in the video. 104 00:04:26,980 --> 00:04:29,510 But you can imagine how temperature and pH might 105 00:04:29,510 --> 00:04:30,905 affect your reaction rate. 106 00:04:30,905 --> 00:04:34,250 And finally, ocean acidification linked to climate change 107 00:04:34,250 --> 00:04:38,440 is causing our seashells to dissolve, which is very sad.