Soluções - classificação, soluto e solvente, curvas de solubilidade e exemplos.
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Soluções são mais comum do que parecem, vão desde um copo de água com açúcar até uma medalha de ouro. Como contexto básico soluções são classificadas como misturas homogênea, ou seja, duas (ou mais) substâncias puras misturadas e uma única fase visível.
Soluções podem ser classificadas, com base na concentração de soluto, em: Soluções insaturadas; Soluções saturadas; Soluções saturadas com corpo de fundo; e Soluções supersaturadas. veja isso e muito mais nessa vídeo aula, espero que a aula venha a lhe ajudar em seus estudos. Até a próxima.
00:00Hey there, people from my channel, my students, former students and future students, welcome once again to our Illustrious Chemistry.
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00:16And now let's move on to our solutions content, which is very common content in relation to entrance exams, Enem and, of course, my tests, right?
00:26First thing, guys, we have to understand what solutions are.
00:33Solutions are classified as homogeneous mixtures, that is, mixtures that have a single visible phase and two or more mixed substances, in this case, pure substances.
00:50But here it is a relationship of pure substance, homogeneous and heterogeneous.
00:57I have here that, for example, when I talk about the pure substance water, in this case here, I will only have H2O molecules, nothing more than that.
01:10When I talk about the pure substance sodium chloride, I only have NaCl molecules, with water being my universal solvent and NaCl being my solute.
01:24Continuing here in homogeneous mixture, in this case, now I will have water plus NaCl, that is, water plus salt.
01:43Since I dissolved it in a proportion that the salt was completely dissolved, that is, my solute plus my solvent, forming only one visible phase, right?
02:00And finally, in our definitions, we now have a heterogeneous mixture.
02:09When I say straight, here I will have, for example, water plus oil.
02:16In this case, they will not mix.
02:19Why?
02:19Water will be the polar molecule and oil will be a nonpolar molecule.
02:25So, there is no way for them to interact, there is no way for there to be solubility in this case.
02:33Coming back, I also have that these solutions of mine can be solid, liquid and gaseous.
02:50Contrary to what we think, they would only be liquids.
02:54For example, in the gold medal, in this case here, I will have a mixture of 92.5% silver, 6.16% copper and only 1.34% gold.
03:09In other words, I have almost no gold.
03:11Here I have a metal alloy, that is, a mixture.
03:17In this case, a homogeneous mixture.
03:21Going here, to the second example, I have sea water.
03:26Sea water will be made up of 96.5% H2O and only 3.5% of other salts, such as magnesium, chloride and others.
03:39And finally, we have the atmospheric, that is, a gaseous example, where I have the mixture of nitrogen gas, 78%, oxygen, 21% and water vapor and other gases, just 1%.
03:53And all these examples form just one visible phase, right?
04:02In other words, they are all examples of homogeneous mixtures.
04:08Be careful that when I talk about a heterogeneous mixture, they are not solutions, they will not be considered solutions.
04:16But to be a solution, the prerequisite is to be homogeneous.
04:19And finally, I have here that they are formed by solute and solvent.
04:26So, from my solute in smaller quantity, in the example, it was NaCl and in larger quantity, I had water.
04:40Moving on, let's understand what the solubility coefficient is, right?
04:44Basically, it is the maximum amount of solute that can be solvated by the solvent in, for example, 100 grams or MLs of water,
05:03being at a temperature of 25 degrees and a pressure of 1 atm.
05:12Let's analyze.
05:13Suppose that in 100 grams of H2O, the maximum number of NaCl cubes that can be dissolved is 3.
05:24This maximum will be called the solubility coefficient.
05:30Based on this, the following observations can be made.
05:33In the first case, notice here, all the containers here will have 100 ml or 100 grams of water.
05:47In the first one, I have that I'm going to add just 2.
05:52So here, I can say that 2 is not enough, right?
06:00I am below the coefficient.
06:12I can add more cubes, right?
06:16In the other case, now, I have 3.
06:21So here, 3.
06:263 is good.
06:27Since it is exactly my coefficient.
06:34That is, I say that I am equal to the coefficient.
06:42In this case, my solution is exactly at its maximum coefficient.
06:46I can't dissolve anything else.
06:48And in the last example, I have 4 cubes, and the maximum I can dissolve is 3.
06:53So here, it will turn out that 4 is too much.
06:58In other words, I have 1 cube that will not be dissolved.
07:03And at that point, I'm above the coefficient.
07:10I can't dissolve anything else.
07:18And here, is the remaining solute.
07:30Let's now move on to solution classifications.
07:34In this case, I have 3.
07:35The first one, I will classify as unsaturated.
07:39And in that case, I can still add more cubes.
07:43It fits a small cube.
07:45Remembering that my coefficient here is 3 cubes of 12 grams of NaCl for 100 grams of water.
07:57So if in this case I added 1 or 2, I can add more.
08:02Remembering that my experiment was carried out at 25 degrees and 1 atm.
08:06In the second case, I have saturated.
08:11And I can say that I have exactly 36 grams, which are 3 cubes with 12 grams.
08:20So I'm right on the coefficient.
08:23And another case is saturated with background body.
08:25Here, I added 4 cubes.
08:28In other words, I added too much.
08:30And there is the formation of a background body.
08:39Or else hasty.
08:42And these are the 3 classifications.
08:44Now we have one more.
08:46Which is a special case.
08:48Which are super saturated solutions.
08:51That, initially, it is a saturated solution with a background body.
08:59Now we are going to increase the temperature of the system.
09:04The temperature increases.
09:06Thus, increasing the solubility coefficient.
09:11After increasing the temperature and dissolving what I had extra.
09:17And I will gradually decrease this temperature.
09:25Until it returns to the initial temperature.
09:27Since it becomes more solute, dissolved.
09:31In my solution.
09:32For example, from 85 to 25 degrees.
09:36Where I could dissolve only 3 cubes.
09:39I will dissolve more.
09:41But then I have to say that this solution is very stable.
09:43Any agitation, it becomes saturated again with the background body.
09:52So in this case when I increase the temperature.
09:55I can dissolve more solute.
09:58In a solution that would originally dissolve only 3 cubes.
10:05If I increase the temperature, I can dissolve, for example, 4 cubes of NaCl.
10:10Now let's move on to the solubility curve.
10:19So here I have a graph that will be solubility by temperature.
10:25The first case I have is rising tanks.
10:28That is, endothermic dissolution.
10:30In that case, I'm getting hot.
10:33My curve will be classified as increasing.
10:37And it is favored by the increase in temperature.
10:40So when I go there on the chart.
10:42I'm going to have my ascending solubility curve.
10:45In other words, it is rising.
10:47The higher the temperature, the higher the solubility.
10:51In other words, the more I can dissolve in this type.
10:54So, solubility is favored.
10:56The other is descending curves.
11:00In this case, I have an exothermic dissolution with release of heat.
11:09Or it releases heat, right?
11:11It's a decreasing curve.
11:13In other words, it is going down.
11:16And it is favored by the decrease in temperature.
11:23So the more temperature it releases, the greater my solubility.
11:33And finally, I have curves with inflections.
11:37Here, the increase in temperature favors the process up to a certain period.
11:46And then disfavoring it right away.
11:49In other words, I start by increasing the temperature.
11:52The process is favored.
11:54But there comes a time when it begins to decline.
11:57So, I'm going to call this an inflection curve.
12:01Let's now make a relationship between saturation and solubility curves.
12:12Example.
12:13When trying to prepare three solutions A, B, and C, determine the saturation of each.
12:21Notice that here on the chart I have all three, right?
12:25And a solubility relationship by temperature.
12:28Looking at the concentration, it's the same among the three, right?
12:33What is changing here, being changed, is the temperature.
12:38Taking into account each system,
12:41here at a temperature of 20 degrees,
12:46B, 40 degrees,
12:49and C, 60 degrees.
12:52Each one was in a different position in relation to my solubility curve.
13:10The system in A, it was above the curve.
13:17So, I say that this system, it is saturated with background body or precipitate.
13:36And yet I can say that it is also a super saturated solution.
13:39In B, I have to be exactly on my curve, that is, equal to the curve.
13:48So, I have a saturated system, right?
13:54No background body, just saturated.
13:57And finally, C, I have to the solution, it is below the curve.
14:05So here I will have an unsaturated solution.
14:17With that, we classified each solution.
14:21Quite easy, by the way.
14:24Example 2.
14:30When analyzing the graph below, we can see that
14:34the KCL curve is descending.
14:43So here I have the KCL curve, it is ascending, on the contrary.
14:50So, my statement is incorrect.
14:57Letter B.
14:58As the temperature increases, the solubility of KCL decreases.
15:04If it is ascending, then if I increase the temperature, I increase the solubility.
15:08It's also wrong.
15:09Letter C.
15:09KBR solubility is higher than KCL.
15:14And truth.
15:15Here, KBR, KCL.
15:17So, statement C is correct.
15:21Letter D.
15:22The lower the temperature, the greater the solubility of KCL.
15:26It's the opposite.
15:28The higher the temperature, the greater the solubility.
15:35KCL exhibits exothermic solubilization.
15:40In this case, exothermic means that it is a downward curve.
15:47In other words, it releases heat.
15:51We saw that ascending, endothermic, absorbs heat.
15:55So, the correct alternative is C and it was that easy.
16:01And that's it, folks.
16:06That's all for today.
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