Masterclass de Ciencias Naturales (Sesión 7 Mayo - AM)

Hinzugefügt: 2026-05-12

[00:00:00]Teiki Teiki Hello, hello, good morning, welcome to a new natural science session. Let me introduce myself, my name is Javier Rodríguez. I think you've seen me in almost every session, either presenting or doing the social science session. Today I want to introduce you to Professor Paola, who will also be collaborating with us in our social sciences session and is an expert in Natural Sciences.

[00:01:17]Professor Paola, good morning. How are you?

[00:01:21]Good morning, Javier, how are you?

[00:01:23]Good morning everyone.

[00:01:24]Thank you so much for the invitation. I'm so glad to have you in this session.

[00:01:29]Good morning also to Juan David, who is our master, and to Professor Diana as well, who is the master of our Professor Paola.

[00:01:37]I hope you are all doing well.

[00:01:39]Welcome to everyone who is arriving, good morning to Sara Sofia.

[00:01:44]Sara Valentina from the Fernando González Ochoa school. Welcome to all the new participants who are arriving at this natural science session. Hey Juan David, right now in the master class, he's going to post two super important links in the comments in case you don't have them. One, a WhatsApp link so you can join our Accompany Me Masterclass channel, so you can stay informed about all the sessions.

[00:02:08]Two of them will share our support link with us so that you can also keep it in mind.

[00:02:16]So Juan David Arun is already pointing them out. Good morning, and welcome back to our masterclass sessions. Yes, and also a reminder that we have an English session tomorrow, so stay super connected as well. If you haven't subscribed to our Accompany Me Masterclass channel or Academic Network, there's a little red button below.

[00:02:39]Subscribe and hit the bell icon to receive notifications of our live streams. That's all, Professor Paola, I hope you have a spectacular session, and that everything goes very well with all our participants. Okay, we'll see each other next time.

[00:02:57]Well, thank you very much, Javier.

[00:02:59]Once again, good morning to all our dear students who are joining our natural science masterclass right now. It is a space designed especially to strengthen learning in the area of ​​chemistry and also a support for their preparation for the knowledge test, to remember again those concepts that we have seen perhaps in previous years or that we are seeing at this moment. Today we are going to work on several very important concepts such as acidity, vasicity, pH, the formation of solutions and methods of separating mixtures. Remember that this session is not just about memorizing concepts, but also about learning to understand how these substances behave in everyday life and how we apply this knowledge to answer different questions in our lives, at school, at home, in the applicability that chemistry gives us in daily life.

[00:04:13]Okay, next.

[00:04:16]Therefore, let's look at the agenda.

[00:04:19]Um, during the class we're going to have five moments, the welcome moment where we'll also read some of you, who is actively participating in the chat, who is connected, and from which school you are greeting us. Uh, we're also going to move on to a second moment, which is the activation of knowledge. And at this point, we will take the time to analyze some uses of the elements we use in our daily lives and how that understanding of chemistry helps us to know some properties and uses. In a third stage we will move on to the in- depth study of chemistry, that is, we will review those theoretical concepts of the topics that I just mentioned and we will also review how we are going to apply them. Next, we will move on to a point of exploring questions.

[00:05:18]Okay, so here we're going to give that applicability of those concepts through some practical exercises that will also allow me to check the understanding of the topics. And we're going to finish with one last moment, which is the closing, where we'll see a brief summary of the concepts we reviewed.

[00:05:45]So, let's continue, Juan David, and let's get on with the session's objective. But first, let's remind you of what Javier was saying: we have the attendance link, so please don't forget to register. We want to know who was here with us, and you can also leave your comments in the chat, which we'll read so you can actively participate during the session.

[00:06:20]Let's begin then with the objective of the session. What are we going to do today? We will understand the concepts of acidity and vasicity through observation, inquiry, and analysis of everyday situations. So they can explain how these properties influence the behavior of substances. and apply this knowledge to solve problems related to the formation of solutions and the separation of mixtures. Remember, guys, chemistry is life. Chemistry is everywhere. Therefore, it is also fundamental if we understand from the theoretical concepts, we will have a foundation to be able to argue and make informed decisions in science. Therefore, through observation, inquiry, and analysis of everyday situations, this will allow us to examine, for example, some products we use at home: why do they work that way? or why we are also using them for certain purposes and not only in the home, in the environment or processes that can also occur in the human body.

[00:07:36]We will also analyze how these substances can influence the formation of new compounds or new solutions and also the separation of mixtures.

[00:07:49]Likewise, we will also have a prioritized learning during this session, which is to analyze the acidity and vasicity of solutions, fundamental chemical properties that together with the characteristics of the particles define the physical and chemical properties of substances and their daily biological and industrial importance, also considering the physical and chemical changes in nature and the factors that affect their formation. Therefore, this prioritized learning indicates that we must analyze acidity and basicity as a fundamental chemical property of compounds; they are not isolated. All of this is working in a coordinated way. These properties are also related to particles, for example, physical changes, chemical changes, such as the pH of solutions and how these new substances are formed or dissolved in others, and also how these can be separated.

[00:08:48]Therefore, in the learning evidence, we will apply methods of separating mixtures and solutions based on the physical and chemical properties of their components, justifying the appropriate use of techniques such as filtration, distillation, or decantation in an experimental practice. I think we're mentioning some concepts and they suddenly come to mind, like, " Oh, I remember seeing this concept in previous years," or that you're also applying them right now. This evidence of learning will allow us to apply these separation methods, justifying why that technique is used according to the properties of the components.

[00:09:33]Following.

[00:09:37]Therefore, before we begin, I invite you to scan the QR code or click on the link that is currently appearing on the screen and answer this question.

[00:09:53]This question is related to the topic of methods for separating mixtures.

[00:09:59]So, we invite you to come in and respond. Hey, some of the kids are already writing to us here in the chat, saying they're really paying attention to the class. So, we invite you to answer this question with the people who are connected.

[00:10:24]Perfect. So, we invite you to start answering them. Likewise, people who are joining can do so to also test their knowledge. Remember those concepts, as I said, that we have also been working on in previous years, remembering what those mixture separation methods are.

[00:10:43]So, we'll leave it here in the chat too so that people who are joining can also resolve it.

[00:10:51]Next, please.

[00:10:56]Okay, so let's start with the activation of knowledge. In activating knowledge, I'm going to invite everyone to please concentrate and start reviewing some of the elements that I'm going to present below.

[00:11:12]following.

[00:11:16]Ready. So, let's start with this dental routine. The thinking routine is called what I see, what I think, and what I wonder. So, let's start by looking at these products. What products do I have on the slide?

[00:11:35]Then we see a lemon, we see vinegar, we see soap, we see shampoo, we see soda, milk and baking soda. If you notice, these are products that we normally use in our daily lives, in food, and also in hygiene, right? So, let's start looking at them, okay? As the thinking routine says, let's see them.

[00:12:05]So, when we see them, what do we observe? So, here are some questions to help guide us. We are going to describe those colors, those shapes, the uses of the substances. Let's remember, sometimes we overlook those simple things that we can start using, but that we don't analyze.

[00:12:31]Next, we're going to think about what you think might happen with each of these products on my body or when I use them. Why do I suddenly think that some of these substances or products are acidic or basic?

[00:12:51]And then I ask myself, what doubts might arise from each of them?

[00:12:58]What else would I like to know about these substances? I don't know, the pH or why I'm using them then for certain types of moments in my daily life. Yeah? So, here we can also read what comes to mind for you at this moment. For example, uh, sodas, in my case, well, I don't consume them that often, I consume them from time to time, but for example, I do consume milk daily, for example, at breakfast.

[00:13:35]Sodium bicarbonate is a product that we hear has many uses, such as a kitchen cleaner and a laundry cleaner. To be honest, in my case, I hardly ever use them, but you can give them a certain particular use.

[00:13:56]So, I invite you to start thinking about what other uses we can have for these products.

[00:14:03]And I also remind you to start filling out the question I left you from the beginning of "Let's explore knowledge," because this helps us all to activate it, activate it, activate it.

[00:14:18]So, remember, it doesn't matter if we make mistakes right now, guys, it's a learning moment, it's a moment where we 're remembering, and it's a moment where we can also solidify that knowledge.

[00:14:31]Ready? Once we have completed this exercise of what I see, what I think and what I ask myself, we move on to the next slide. And here we also have some explanations.

[00:14:45]So, for example, what I see here I interpret as what I was seeing.

[00:14:50]So, for example, I say, soap, soap can be solid, shampoo is liquid. I begin to describe those first shapes, I can also begin to describe that smell, it's the taste, for example, lemon. We remember the lemon, then you start to say, "Oh, it's kind of acidic, it gives me certain sensations, uh, there's some product that suddenly foams and changes color." Yeah? So what's going on here? Soap, for example, cleans thanks to a combined action between its components and its special chemical structure, which acts as a bridge, so to speak, between water and grease. That special structure, those surfactants, those soap molecules have two different ends. One that loves water is called hydrophilic, and another that loves fat is called ylhydrophobic.

[00:15:48]So, that's when we also started to see that cleaning property. What happens when you wash those molecules or those little tails that hate water? They dig into the grease and surround it to form small spheres called micelles with the dirt trapped in the center. Then, when rinsing, what happens is that those water-loving heads or water-loving molecules are attracted to it, and since they are attached to those micelles, the water carries away that dirt so that it comes out. Ready? So, if you notice, in order for me to do that cleaning process, as I was saying, I normally take the soap, I take a bath, I use it to wash clothes, but we don't think about what's happening at a molecular level, why do I use soap to clean my clothes and not, for example, soda? Yes. So it's because at a molecular level certain chemical reactions are also taking place that allow me to clean them or use them for that purpose. Another example is the lemon.

[00:16:56]Lemons have a sour taste, but why? due to its high content of natural organic acids, mainly citric acid, which is more or less between 5 and 6% of that juice. And this causes them to release a large amount of hydrogen ions, and these hydrogen ions make the pH low, and when it is low, approximately two, it is considered an acidic substance. And what happens when the lemon enters my mouth, at the moment of contact, well, it covers those molecules of the taste buds on the tongue that detect those hydrogen ions that the acid releases and send that signal to the brain of that sour taste.

[00:17:45]Yeah? So, that's why we also have that feeling. I also welcome the new students who are joining us. We already have more people connected.

[00:18:00]Remember to fill out the attendance form and also remember to fill out the question, the link that Juan David left here so you can test your knowledge. Remember, it doesn't matter if we have a wrong answer, the important thing is to activate knowledge. Right now we are learning, we are remembering. So, I invite you to participate. And to conclude this activation of knowledge, let's move on to vinegar. Vinegar is also a substance that we normally use in our home.

[00:18:32]We can usually use it in salads too, but I don't know if you also remember that when you started studying chemistry in the lower grades, we mixed vinegar with baking soda. I don't know if you remember what happens when I mix vinegar with baking soda. I'll give you a few more clues.

[00:18:53]So, we would take a bottle, put a little vinegar in it, a little baking soda, and attach a pump to the mouth of the bottle.

[00:19:02]So, I invite you all to participate as well. Do you remember what used to happen here?

[00:19:07]A chemical neutralization reaction occurs. So, let's remember, vinegar is also known within the field of chemistry as acetic acid. So, it's an acid and sodium bicarbonate is a base.

[00:19:24]Therefore, when I mix an acid and a base, a neutralization chemical reaction occurs.

[00:19:32]If we recall that experiment back then where we placed the little bulb, what happened? The pump was inflating, right? Because? Why is the pump inflating? Because a reaction occurs where we see that this reaction is formed by the... sorry, it reacts forming gas and that gas is carbon dioxide. They're already telling us here what the difference is between an acid and a base. I don't remember. Don't worry, Juan, we'll go in and check it right now.

[00:20:07]Let's remember again what a base is, what an acid is, don't worry.

[00:20:12]And here we go. So, as I was saying, the chemical reaction takes place, it produces carbon dioxide, and that gas that comes out is what inflates the little balloon. Yeah?

[00:20:22]So, there we also see that there is bubble formation, there is foam. Yes, those are my final products.

[00:20:29]So, whenever we see this kind of scientific evidence, it's what allows me to say, "Ah, a chemical reaction is happening." Ready. Finally, we can conclude that these everyday products are chemical substances that have specific properties, guys. That's why I told them, chemistry is in everything. It's just that we sometimes go unnoticed; we take a bath, we drink lemonade, for example, we use vinegar, our food too, but we don't think at a molecular level about what's happening. What else can we conclude?

[00:21:11]Well, some substances are acidic like lemon, like vinegar, others are basic like soap, baking soda, and others are almost neutral pH like water or milk. The key is that their properties depend on the particles that compose them and also on how they interact with other substances.

[00:21:34]Now we're going to move on to the component of exploring that knowledge. Then, let's continue, please. We're going to look at that next in-depth chemistry and we're going to remember what acids and bases are. As Juan told us in the chat, I don't remember, don't worry. And here we're going to do a brief review of where that definition of acids and bases came from. Then, in the 1800s, the first scientist, Mr. Arrenius, appeared and began to talk about this terminology.

[00:22:15]So what does Arrenius tell us?

[00:22:17]Arrenius tells us that an acid is a substance that releases hydrogen ions, that is, H+, that is, the ones we are seeing on the screen, H+, which we also know as protons, right? or hydrogen ions and it is a hydrogen ion because it has a positive charge. An ion, remember that it is that element that has a charge and a base is a substance that releases hydroxide ions, that is, OH-. We are also seeing it within the example, the basic definition. That's why we remember just now when I was telling you what happens with the lemon, it's an acidic substance that releases hydrogen ions. Therefore, when it makes contact with my taste buds on my tongue, it sends a signal to the brain which detects it as an acidic taste. Ready. Here we are also seeing in the slide, for example, hydrochloric acid. Hydrochloric acid, guys, is one of the compounds that we study the most within the courses. So, hydrochloric acid is HCl, which we are seeing here, which when dissolved in water separates into hydrogen ions H+ and chloride ions Cl-.

[00:23:46]This means that the concentration of protons in the solution increases, making it acidic. Ready?

[00:23:56]On the other hand, let's look at the basic definition. We see sodium hydroxide. Sodium hydroxide is also a compound that we work with a lot in chemistry classes.

[00:24:08]So, I think that's also why they can easily recognize him, that it's Na.

[00:24:15]And when it is in water or in solution it dissociates, that is, it separates by releasing sodium ions Na+ and hydroxide ions, which are OH-, increasing its concentration of hydroxide ions, which makes it basic.

[00:24:34]This model is useful, but it has a major limitation. What happened to Arremius? That only applies when the compounds are in water. It does not explain when the compounds are in another type of medium. So what happened? Well, to overcome that limitation, the scientist Broen Lowy appeared in the year 19.

[00:24:57]Uh, to overcome the limitation, as I say, well, this model not only depends on water, but also on something more important. And here Broen talks to us about proton transfer, guys. And this is one of the theories that has stood the longest over time and is the one we work with the most because it has no limitations.

[00:25:20]Therefore, we will focus primarily on brastone. What does that mean?

[00:25:24]An acid is a substance that donates a proton. What are protons?

[00:25:32]H+ again.

[00:25:35]And a base is a substance that accepts protons, that is, that accepts H+ ions.

[00:25:44]Let's look at an example. So, in the example they are telling us, I have hydrochloric acid HCl+ water.

[00:25:53]What's happening? that hydrochloric acid, that is, HCl, dissociates and releases the hydrogen ion or proton, that is, H+.

[00:26:06]What happens to that ion? It is added to the water molecule.

[00:26:12]That is, when the water molecule receives that proton, it becomes the H3O+ molecule and ceases to be water, becoming the hydronium ion. Ready? So we're seeing it in the reaction. What about chlorine? Well, chlorine is also released and remains as chlorine ions. What's going on here, guys?

[00:26:41]that hydrochloric acid donated, as I defined it, a proton to the water. Therefore, by donating, it means that hydrochloric acid is an acid and water, by receiving that proton, is a base. Ready?

[00:27:03]So, here we see that definition and a new compound being formed called the hydronium ion.

[00:27:12]This in turn generates other concepts called conjugate pairs, but we'll see that a little later, but I'll warn you. Ready?

[00:27:25]Then, with Bronen and Lowry, this new concept called conjugate pairs emerged. And what does this mean?

[00:27:32]That when an acid loses a proton, it becomes its conjugate base.

[00:27:39]And when a base gains a proton, it becomes a conjugate acid. Ready?

[00:27:47]But don't worry, we'll come back to it later and explain it in more detail.

[00:27:54]In this model there is always proton transfer. There cannot be an acid without a base, because it would not receive that proton.

[00:28:02]Ready? Finally, we arrive at Lewis's model. In the Lewis model, it is a more general model; Lewis also tells us that it is no longer about protons, nor about the release of ions, but about electrons.

[00:28:23]So, Lewis tells us that an acid is a substance that accepts electrons and a base is a substance that donates electrons. So, we're going to look at this in a very general way as well.

[00:28:40]As I said, the theory that we stayed to study is Broen's.

[00:28:46]Lewis also made this model much more general, but based on electrons. And what does Lewis tell us? Let's look at the example. So, for example, boron trifluoride.

[00:28:57]What will boron trifluoride do? It will capture that electron pair from the ammonia. So, since it has an electron deficit, it accepts the pair from ammonia, and ammonia also accepts them. What happens is the formation of a coordinate covalent bond, where both electrons of the bond come from the same substance, in this case the base. And in the Lewis model we no longer talk about protons, we no longer talk about water, we only talk about the exchange of electrons. So, to summarize, Arrenius tells us about the release of hydrogen ions and hydroxyl ions in water. Broen talks about proton transfer and Lewis talks about electron transfer.

[00:29:50]Arremios works in water, Brustin explains protons, and Lewis explains electrons. But we're going to focus, as I was saying, on broasted chicken. So, let's move on to the next slide.

[00:30:05]We are going to look at those acids and bases of Brosten and Lowy because with them we are going to study these cases of acidity and basicity much more.

[00:30:17]Uh, according to this theory, an acid is a substance that donates protons, that is, H+. A base, on the other hand, is a substance that accepts them. So, let's look at the graph we have on the screen and let's look at that reaction. So, in the reaction we have hydrochloric acid and we have water.

[00:30:45]What am I seeing happening here? The acid is donating its proton to the water molecule, forming the hydronium ion, that is, H3O.

[00:30:59]Why is H3O formed? Because the water received the proton that the hydrochloric acid is donating, and I have chloride ions left over. That's the general reaction I'm experiencing between the acid and the water. We'd also like to see you in the chat if you'd like to share some of your thoughts.

[00:31:24]Let's look at the following example, but we're also going to look at it at the electronic level, that is, what's happening with the electrons? So, let's move on to the next slide.

[00:31:37]Let's look at this slide, guys.

[00:31:41]So, we have the same example as before, but let's look at the electrons. Let's remember that hydrogen has one valence electron and chlorine has seven valence electrons, that is, here we are forming hydrochloric acid.

[00:32:01]We also see the water molecule. In the water molecule, which is made up of two hydrogen atoms, each with one electron. And oxygen has six valence electrons. Then we see each of these compounds formed with their electrons. So what do we see? What's going on?

[00:32:27]That the hydrogen atom will join the water molecule.

[00:32:33]So, we can see what's happening after the arrow on the products. Oxygen now has around it not just two hydrogen atoms, but three.

[00:32:45]That third one appeared due to the donation of the hydrogen atom from hydrochloric acid, that is, the hydronium ion was formed and chloride ions were also released.

[00:33:04]Ready? We can see that more students are connecting here as well.

[00:33:09]Welcome, guys. Hey, there's still time for them to join.

[00:33:14]You can also review the video as many times as you wish.

[00:33:19]Uh, you can also share it with your classmates to review these concepts that we are remembering. So, welcome colleagues, welcome students. We're also going to review that QR code or that link that Juan David left you at the beginning so you can also answer it, activate that knowledge, and we're going to go over it throughout the class.

[00:33:51]Ready? So, here's our example to see what's happening with brosten and lour acids. So, it is now completely clear to us that an acid is one that donates that hydrogen or that hydronium ion to a compound so that a base is also formed. So, let's move on to the next slide.

[00:34:18]Let's look at this reaction, for example.

[00:34:22]This compound CH3COOh is acetic acid. Acetic acid is the one we started mentioning at the beginning, I don't know if anyone remembers.

[00:34:36]Acetic acid is vinegar. Ready?

[00:34:39]So what happens when I have acetic acid in water? So, let's look at the reaction here. So, the reaction shows that it interacts with the water molecule and transfers a proton to it, that is, the hydrogen that is in red is transferred to the water molecule that I am going to obtain.

[00:35:02]So, let's remember, after the little arrow are the products, before the little arrow are the reactants.

[00:35:07]So, let's look at the products. in the products that I am seeing that the acetate ion was formed. So, you realize, the hydrogen atom disappeared, but the hydrogen atom of that molecule, of acetic acid, because the hydrogen now went to form the hydronium ion, that's why I'm forming H3O.

[00:35:28]Ready? So here I am forming that acetate ion. What does reaction B mean? What do you mean, teacher? Hey, you can return the hydrogen. Yes, here we are seeing that it can be a balanced reaction. Let's also remember the topic of reactions. There are reactions that can also go to the right, they can shift towards the products or towards the reactants until they find an equilibrium. Thanks a lot. We are also seeing the participation of Ronal, a graduate student from the Gustavo Restrepo school. Welcome.

[00:36:03]Thank you so much for participating.

[00:36:07]In other words, this reaction of acetic acid is a reversible reaction that can occur in both directions until it finds a chemical equilibrium.

[00:36:19]Ready? Let's move on to the next one.

[00:36:24]Perfect. Now let's get down to basics. The base of Broen and Lourry. Now we see that, according to Broen, the base is that substance capable of accepting a proton.

[00:36:41]Ready? So, he's no longer donating it, but accepting it. Let's look at the example, ammonia. Ammonia is a typical example of a base and when it dissolves in water it accepts a proton.

[00:36:53]So, let's review that reaction.

[00:36:56]Ammonia is the compound NH3 and we see that it is reacting with a water molecule, therefore we see that the water dissociates and passes a proton to the ammonia. And the ammonia then remains as the ammonium ion, that is, NH4.

[00:37:19]Water acts as an acid because it donates the proton, and ammonia acts as a base because it accepts it. As a result, NH4+ called ammonium ion is formed and negative OH ions, which is the hydroxide ion, are released. That's why it's an ammonia solution. Ammonia solution is an acidic solution because it increases the presence of hydroxyl ions. OH in water. Ready. So, those are examples of what an acid and a base are according to Broen and Low. Let's move on to the next slide. Do you remember when we were looking at the definition of acids and bases according to Brosten and Laurry? We were also talking about how conjugate acids and bases were also being formed. But then you're going to say to me, "Well, professor, where does this 'conjugate base' thing come from now?" This theory incorporates the concept of conjugate acid and base, where there is a competition for protons that occurs in the following way.

[00:38:37]So, let's look at a little example. So, if you notice, a general example, something generic. So, we see that acid plus base will produce a conjugate acid and a conjugate base.

[00:38:54]But if you notice, the acid that is in the reagents, that is, before the arrow, will form the conjugate base. Yeah?

[00:39:06]And the base that the reactants are in will form my conjugate acid pair in the products. Let's look at it with an example, since we have a chemical substance here in the diagram. So, let's see, the acid is hydrochloric acid HCl, which we have already been studying. The base is water, the hydronium ion and chloride ions are produced.

[00:39:37]What's going on here? So, hydrochloric acid is donating its proton to water, and if you notice, hydrochloric acid will form my conjugate base, which would be the chloride ions.

[00:39:56]Ready? And the same in the water. So, let's look at the base. The base is water. The base is forming its conjugate acid pair, which would be the hydroxide ion. Let's move on to the next example, which is hydrofluoric acid. So, let's move on to the next slide.

[00:40:18]Okay, before we move on to this slide, we see more people connected here. Welcome again, welcome everyone. Hey, start activating your knowledge. Let's also remember to fill out the attendance form, the question we had in the QR code. So that your participation is also registered, and well, also pay close attention here in the chat to review those participations that you want to give us. Okay, so here's an example. Let's look at the example of an acid and a base.

[00:40:54]In our first box, which is in red, we're going to see acid. We have hydrofluoric acid, which is HF, which is an acid, plus the base, which is water. So, who would be my conjugate acid? the hydronium ion plus the conjugate base which would be the fluoride ions.

[00:41:19]And in our blue box, which is the base, we're going to have the typical example we were just talking about, ammonia, plus the water molecule will also form the ammonium ion which is NH4+.

[00:41:36]Therefore, it would be my conjugate acid plus the conjugate base, which would be the hydroxide ions.

[00:41:46]Ready?

[00:41:48]This is more like a play on words.

[00:41:50]Uh, it's just that if you have any doubts, you can check it again.

[00:41:56]But really, guys, these are concepts of acidity and vasicity, which are also very important for you to apply in your daily exercises in chemistry, their applicability also within daily life and we will see it also within industry and even in the reactions that occur in our human body. So, to help us understand, we already know what an acid is, what a base is, and we're going to see what types of acids can exist. So, let's move on to the next slide.

[00:42:40]Classification of acids. So, within the acids that we have studied, there are inorganic acids and there are also organic acids. The vast majority of those we have been studying are inorganic. So, within those inorganic acids we find that there are triprotic, diprotic and monoprotic acids. What does that mean, teacher?

[00:43:11]triprotic when they have three hydrogen atoms in the compound. For example, phosphoric acid, H3P4.

[00:43:23]Ready? Diprotic when it has two hydrogen atoms in its molecule.

[00:43:31]For example, sulfuric acid H2SO4 is monoprotic when there is only one hydrogen atom. For example, hydrochloric acid or floridic acid, which we just saw. But what's up, guys? When chemical reactions occur, these acids can ionize several times or multiple times depending on the number of hydrogens they have in their molecule.

[00:44:04]For example, the monoprotic only has one hydrogen atom, which can continue to dissociate and ionize, right? Because there are no more hydrogens. But if we go to the other side where there are compounds that have, uh, three hydrogen atoms in their molecule, well, how many times can they be ionized? Three. Ready? And here we are seeing it on screen.

[00:44:29]So, we have H3PO4.

[00:44:32]If a first ionization is done, then we will have H2P4 afterwards, but if ionization continues, it will remain as HPO4.

[00:44:43]Ready? And with the diprotic compound, it can be ionized twice, that is, it would go from H2SO4 to HSO4.

[00:44:58]Ready? This classification allows us to understand that some acids can generate more than one ionization, which also influences their chemical behavior and the acidity of the solution.

[00:45:14]So, this is to make it clear, the types of acids that can exist and they can also be classified according to the number of hydrogens they contain in their molecule. Let's move on to the next one.

[00:45:32]Let's now look at some more qualitative information. What are the properties of acids?

[00:45:40]Therefore, acids have several characteristic properties.

[00:45:45]One of the things we just saw is that they produce hydronium ions. Yes. Uh, they have a lower pH than yes.

[00:45:55]They can react with bases to form salts and water in a process called neutralization.

[00:46:05]Remember when we activated knowledge, guys, at the beginning we talked about the reaction between vinegar and baking soda.

[00:46:14]So, vinegar is also called acetic acid, which we also saw a little while ago in an exercise. And when it reacts with sodium bicarbonate, which is a base, it forms a neutralization reaction.

[00:46:30]Acids also react with carbonates and bicarbonates, forming carbon dioxide, which we observe or evidence with the formation of bubbles. When I told you, kids, remember that experiment we did or that many of you did with the little bottle, you put the balloon in, it inflated, that's because that effervescence is produced, those are those bubbles, that carbon dioxide and also those acids react with metals and release hydrogen. Ready? Let's also look here within the image at what type of solutions can be considered acidic. So we have things like lemon juice, vinegar, sodas, generally Coca-Colas have phosphoric acid, so they give it that acidic taste, uh cleaners, uh acids for cars, for engines. Ready? So, that's also part of the acids. Someone might say to me, "Oh, teacher, so do we consume acids then?" Yes, of course, we can also end up consuming, but not all of us. Of course, because of their chemical properties, we cannot ingest all compounds that are acidic, but only those that are truly suitable for human consumption. Ready? Let's move on to the next slide.

[00:48:01]Let's now look at the properties of bases.

[00:48:05]Bases produce hydroxyl ions, remember? The OH- in water or accept protons. They have a pH greater than seven, their sensation can be soapy, slippery and they have a bitter taste, although these chemical substances should never be tasted.

[00:48:29]Bases react with acids to form salts and water.

[00:48:36]Once again we return to the example I mentioned between vinegar and baking soda. So, bicarbonate is basic, vinegar is acidic, so they form a neutralization reaction.

[00:48:49]They also change the color of the indicators. Now we're also going to look at how CPH is measured and how those pink substances can magically change to colorless.

[00:49:01]A common example is soap and bicarbonates, which are basic substances, and their behavior is also related to the presence of particles that interact with acids or fats. So, let's look at some examples here. Some of the products, generally speaking, are like cleaning products, where we see that the vast majority of them are basic products. So, for example, we see soap, shampoo, baking soda, detergents, ammonia. Ready? Uh, they're usually of this type of property.

[00:49:41]Let's move on to the next slide.

[00:49:46]Let's take a look. But, teacher, you don't quite remember what pH is. You mention pH.

[00:49:51]pH, so let's remember what pH is.

[00:49:55]pH is a measure that indicates how acidic or basic a substance is.

[00:50:04]And here we see our pH scale. The pH ranges from 0 to 14.

[00:50:13]If the pH is less than 7, the substance is acidic.

[00:50:19]Ready? Let's look at some examples.

[00:50:22]So there we have the lemon, the vinegar. So let's see, the lemon is between one and two, the vinegar is at three, the tomato juice, the coffee reaches between five and six. Ready? These are some of the substances found on the acid scale. If it is greater than seven, the substance is basic. So, we're now going to the other side of the scale. What do we have there?

[00:50:55]We have seawater, we have baking soda, the soap is around 11 or 12. Mm.

[00:51:03]But what if it's seven? Seven is neutral. Ready. They are neutral substances.

[00:51:10]Here we will find, for example, things like milk, like water. They are neutral substances.

[00:51:17]pH is related to the concentration of hydronium ions. Ready? Therefore, the higher the concentration of hydronium ions, the higher the pH acidity. Ready. Again, the higher the concentration of hydronium ions, the greater the acidity, the lower the pH. So there we can see some of the examples that we find on this pH scale. And we'll also see some applications of pH, guys. For example, if I go to a swimming pool, I also have to check the pH of the water because what if it becomes acidic or has an acidic pH, well, I'll get burned. So, pH measurement also needs to be done in agriculture.

[00:52:19]The pH of the soil, of the earth, if the soil does not have a specific pH, a plant cannot grow. Therefore, we need a suitable pH. So, in agriculture I also need to measure that pH, as I was saying, also in water treatment, in health, in the stomach I have gastric juices and we're going to look at that too, uh, in my stomach there is also an adequate pH. That's why sometimes people say, "Oh, I have gastritis, I have heartburn." Yes.

[00:52:54]So that pH is very low.

[00:52:57]And in hygiene we also have some of those products that are useful for cleaning.

[00:53:06]Let's move on to the next one.

[00:53:09]So, as I was saying, let's look at where I use that pH in everyday life. So, let's look at household cleaning, soaps, detergents, what I was explaining to you at the beginning, guys, how soap cleans.

[00:53:23]Yes, it's not that the bar magically rubs off when I pass it over the clothes, no. At a molecular level, chemical reactions are also taking place that cause the fat to be eliminated.

[00:53:37]Vinegar is acidic, and although vinegar can be consumed, it is also sometimes used for cleaning. The human body also contains hydrochloric acid to help digest some foods and also to eliminate some bacteria in toothpaste, right? It is also slightly basic and neutralizes some acids.

[00:54:03]Let's move on to the next one.

[00:54:09]Let's look at the industry, as I was saying, that water treatment, I have to adjust that pH, the pH also in some media, if they are acidic or basic, certain types of bacteria can live or die.

[00:54:27]So if I need some bacteria to live, I have to look at what the best medium is for that bacteria. But if I want to eliminate the bacteria, then I have to look at which environment is not favorable to it so that I can eliminate it. Ready? Let's look at food production. Acids are used for preservation, for making preserves, such as acetic acid, to control bacteria, to improve the flavor, texture, and shelf life of these foods.

[00:54:58]In the environment, guys, acid rain, in acid rain, in some parts of the world you can already see how it deteriorates some of the monuments that are made of bronze, and when that acid rain falls it also deteriorates them, or clothes too when they are left out to dry.

[00:55:19]So, in some parts of the world, these effects are much more pronounced, as they are also affecting plants, soil, and water.

[00:55:31]Ready? And what I was telling you, they start to cause that corrosion of some elements that are in the environment, of buildings, of monuments. Hm. And that pH also affects the rivers, so it can affect, as it appears here in the diagram, the pH can affect all types of ecosystems.

[00:55:56]So, if the waters of a river or any water source are also altered, it can also affect the life that exists within that ecosystem. So, well, it can affect the fish and the plants that live there.

[00:56:18]Let's move on to the next slide.

[00:56:23]Ready? But, teacher, how do I measure pH?

[00:56:27]So, guys, I don't know if some of you remember that you also reviewed this topic in class or went to the lab to do these kinds of experimental practices. So, we're also going to have to review three types of measurement. How can we measure them here? So we see that pH can be measured initially with a pH meter, which is a much more specialized piece of equipment, giving a much more precise measurement. Yes, these particle meters will also be in spaces such as laboratories, well, much more specialized ones.

[00:57:13]Uh, there is also a much simpler measure, which is litmus paper or indicator paper.

[00:57:20]You might remember that. So, this paper changes color according to the pH.

[00:57:26]And finally, there are also indicators.

[00:57:30]Phenolphthalein is also found in the indicators.

[00:57:32]Suddenly that's also the most well-known, the one we can remember. Uh, natural indicators can also be used. We can also make a natural indicator in the laboratory from an extract, for example, from red cabbage. Hm. And each method has a different use.

[00:57:51]So, for example, if the PHRO is a more specialized, more accurate piece of equipment, then it will also be for processes that require that precision in their data, while the others are much faster, cheaper measurements, right? So, let's look at some examples. So, let's move on to the next slide.

[00:58:17]So, let's watch this video on how litmus paper works.

[00:58:30]Here we have two substances. Imagine that you don't know the name of this substance and that you want to know if it is an acid or a base. To detect whether a substance is an acid or a base, we can use some indicators. We have two types of indicators, or I want to mention two of them, which are the ones we 've been seeing on the channel. The first indicator is this, it is called blue litmus paper. It is a litmus paper that is blue in color. This blue litmus paper is used to identify substances that are acids.

[00:59:07]When you immerse or wet this paper in one of the substances and it changes to red, it means that the substance is acidic. We are going to do the test with this substance, with substance one, which is the one you are observing on the right side of your screens. I'm going to put the blue litmus paper into the substance. If blue litmus paper turns red, it means the substance is acidic.

[00:59:34]I'm going to put it in and take it out now. I'm bringing it closer to the camera so you can see. And here we can see that the paper that did not get wet, which is the top part of the litmus paper, remains blue.

[00:59:50]But the part that did manage to get into the substance has a red color. Yes.

[00:59:57]What does that mean? That substance number one, this substance is an acidic substance by means of blue litmus paper. Now I'm going to introduce another piece of blue litmus paper. I cannot enter the same one I just used because that one has already been used. I'm looking for a new blue litmus paper and I'm going to put it into my substance number two, which I don't know what it is.

[01:00:23]Remember, if the blue litmus paper turns red, then substance number two should also be an acid. At this point, I am introducing litmus paper, removing it, and as you can see, there is no change in color; on the contrary, the paper only became moistened, but there was no change in color. What does that mean?

[01:00:44]This substance, substance number two, which is the one you are observing on the left side of your screens, this substance is not acidic.

[01:00:54]For this reason, it should be considered a base. But what indicator can we use to find out if substance two, which in this case is not acidic, is a base? Well, there is another indicator which is red litmus paper.

[01:01:10]This paper is very similar to the previous one, only it is red. This is used to identify bases.

[01:01:17]If red litmus paper turns blue, it means the substance is a base. I'm going to introduce it into substance number two and we'll see if it changes color. We put it in, we took it out, and here, as you can see, there is a change of color. The top part, which was the part of the paper that did not get wet, is still red, but the bottom part has a noticeable change to blue, which means that red litmus paper is used to identify substances that are basic or alkaline, while blue litmus paper is used to identify acidic substances. In conclusion, the second substance we have here in this container is chlorine and it is a base or alkali. And the number one substance we have in the container on the right is acid. This container holds an orange juice substance that we can drink. Remember that in chemistry you should not ingest the substances used in the laboratory. If the substances are contaminated.

[01:02:35]Perfect. Thank you very much, Juan David.

[01:02:37]So, here we saw that litmus paper changes color depending on the medium. In an acidic medium, blue litmus paper turns red, and in a basic medium, red litmus paper turns blue. So, these are experiments that are easier to do in a laboratory. Let's move on to the next slide.

[01:03:02]In the next slide we will find out what happens to phenolphthalein.

[01:03:08]Phenolphthalein too, because sometimes in some schools it can be found and used for these types of experiments. So, for some it may seem like magic, but let's see what's happening at a molecular level to make it change color.

[01:03:23]So, go ahead, Juan David. an experiment that seems like magic.

[01:03:50]But what's the catch? We have three containers. To the first one we add about 200 ml of water and one or two flakes of sodium hydroxide. Caution, be very careful because sodium hydroxide is corrosive. To the second container we add about two or three drops of phenolphthalein and since it is such a small amount, even if you turn it upside down, they do not fall out. And finally, to the third container we add about 20 ml of vinegar. The key to this experiment is phenolphthalein, which is a pH indicator and changes color depending on whether it is in a basic or acidic environment. In basic solutions like sodium hydroxide, it turns pink, and that's why you observe this color change. But when added to the solution containing vinegar, it turns colorless, since vinegar, which is an acid, reacts with sodium hydroxide and neutralizes the solution. As a result, the pH drops below the range in which phenolphthalein is visible, and that is why it becomes colorless. It really does seem like magic.

[01:04:46]Thank you, Juan David. Exactly.

[01:04:47]So, if we realize, phenolphthalein is an indicator that, when it is colorless, is in an acidic environment, okay?

[01:05:00]But it turns pink when it's in a basic medium, and that's where we saw it. So, when it's with sodium hydroxide, which is a basic solution, that's why it gives that purplish, lilac coloration, right? And when it was in vinegar, well, vinegar is acidic, that's where it becomes a colorless solution. And we're going to the last video where we'll find out how, starting from a natural indicator, we can also measure the pH of substances. So, let's watch the video from here to here, because in a very easy way, we only need this, a red cabbage.

[01:05:56]Hey guys. How are you? Hello, colomarda. We're going to do a really cool experiment today and we're going to observe how, thanks to the purple red cabbage, when combined with different compounds that we have at home, they will change color as always. The first thing we need to do is chop the cabbage a little.

[01:06:24]We poured it into a jug.

[01:06:29]We heat water. It's starting to boil over.

[01:06:41]We stopped and poured the hot water into the jug. We'll stir it a little, and let it rest for a few minutes, okay? And now we're going to see how red cabbage with water turns blue.

[01:07:16]As?

[01:07:17]Yes, instead of water, sparkling water turns blackberry or pink. If we add sugar to the water, it's similar, isn't it?

[01:07:41]With a can of Sprite and you can drink it with a lemon.

[01:07:55]Lemon juice.

[01:07:59]We also mix it with pink water. And if we add baking soda this time, I think you'll help me get it out, Juan David. And here we got it perfect. So here you can see it in its entirety, right? Guys, what are they telling us here? That this indicator, with that purple cabbage, can also identify which solutions are acidic and which are basic? So, if we noticed, the ones that are redder, more vibrant, gave me that acidic indicator. But the ones further to the left, the more purple ones, the blue ones, are the basic ones. Ready?

[01:08:53]So there we can realize, guys, how we can also apply acidity and vasicity and how we can also do it in a simple, easy way in the school laboratory, of course, always with the supervision of the teacher.

[01:09:09]We're going to continue from all this, guys, because we're also going to review that matter undergoes changes and can undergo physical and chemical changes when certain types of reactions occur. So a physical change is when it occurs in a substance because it retains its nature. So, let's look at the key definition in changes of matter. A physical change is a transformation in which its nature does not change, but a chemical change is a transformation in which the nature of matter does change. What does that mean, teacher? I don't understand, then, that in a physical change, uh, for example, when ice, as we see in the image, melts, for example, it goes to a solid state, uh, sorry, uh, it goes to a liquid state, and if I heat that liquid, the water, what's going to happen? because it turns into steam. In other words, the matter only underwent a transformation in its change of state; it always remained water. Ready? So, at first it was in solid form, then in a liquid state, and then in a vapor state. But what happens, or what is the contrast, then, with chemical change? Well, in chemical change that transformation does occur and therefore there is a generation of new substances. For example, what we are seeing is that when paper burns, it forms ash and gases. What does that mean? That I can no longer reverse that reaction. Its nature has changed; it can no longer remain the same original role. For this, we are going to look at some exercises. So, let's move on to the next slide.

[01:11:15]So, for example, here when they tell us that the snow that falls in winter melts when spring arrives, it is a physical change because there was only a change of state.

[01:11:30]In a petrochemical plant, a plastic polymer is obtained from petroleum derivatives. This is a chemical change because it is a transformation of the substance; a metal bench heats up in the sun, physically, only a change in temperature.

[01:11:51]heating.

[01:11:53]Well, by heating the liquid water contained in a container sufficiently, it boils and transforms into physical water vapor, as we also saw at the beginning.

[01:12:04]Through a process called electrolysis, water is broken down into oxygen and hydrogen.

[01:12:10]chemical because the water ceases to be the H2O molecule and separates into hydroium ions and hydroxyl ions. And if bread made from wheat flour is baked in the oven, it's because the flour already undergoes a reaction to become bread. Ready? So there we can clearly see what the difference is.

[01:12:40]between a physical change and a chemical change. Let's move on to the next one.

[01:12:49]Likewise, when changes and reactions occur, there are factors that affect the formation of these new solutions, and this depends on the interaction between the solute and the solvent, with the polarity of this factor being key.

[01:13:10]Let's look at some examples of those factors that affect training. So we have a first factor which is temperature. So temperature has a significant influence, since as heat increases, the movement of particles generally increases, right? And what it does is increase the solubility of those solids or those liquids. Yes, but it also decreases in gases. So there we can see an example. In cold water, the particles move slowly, right? But if I heat that container, well, I'm going to make the molecules start moving much faster, right? And increase the solubility of that liquid much more in a reaction. Let's move on to the next one. We'll see an example there. So, in the example we're going to see, we have a graph where we have the amount of diluted sugar versus temperature. So, if we see that at a temperature of 10 gr approximately 7 g of sugar dissolve.

[01:14:32]But if I increase the temperature to approximately 80-90ºC, I see that the amount of dissolved sugar increases to 50g on the graph.

[01:14:46]So, that means that when the temperature increases, solubility also increases. Let's move on to the next one.

[01:14:59]The agitation. Agitation is also one of the factors that increases or accelerates dissolution, and when we stir, for example, a drink, we help the solute to come into contact with more solvent particles and allow the compound to dissolve much more. Let's move on to the next one.

[01:15:26]Particle size. The size of the particle also influences the speed at which the substance dissolves. So, when the particles are smaller, you have a larger contact area with the solvent.

[01:15:38]That's why powdered sugar will dissolve much faster than a sugar cube. Therefore, the smaller the particle size, the greater the contact surface and the faster the dissolution.

[01:15:52]Ready? Let's move on to the next one.

[01:15:56]The nature of the substance. So, for example, the nature of the substance also influences its solubility, since there is a rule that says, like dissolves like. This means that polar substances dissolve better in polar solvents such as water. In contrast, nonpolar substances dissolve better in nonpolar solvents. For example, salt dissolves in water because there is an interaction between the salt and the water, but oil does not dissolve in water because it does not have the polar nature of water. Let's move on to the next factor.

[01:16:41]Concentration. So, concentration is also another factor that helps with solubility. For example, this depends on the amount of solute dissolved in a given amount of solvent. If we add more solute, the concentration increases, but there will come a point where the solvent can no longer dissolve any more solute. Therefore, at that point we consider that the solution is already saturated.

[01:17:09]If we continue adding more solute, the excess will remain at the bottom and will no longer dissolve, as we can also see in the image. Therefore, we can find unsaturated, saturated, and supersaturated solutions.

[01:17:23]Let's move on to the next one.

[01:17:26]When we look at these factors, we also see how they can affect the solutions that are formed, because here we also find that homogeneous mixtures and heterogeneous mixtures can be formed. So, let's see what the differences are. A homogeneous mixture cannot have its components distinguished with the naked eye, but a heterogeneous mixture has a non-uniform composition. You can distinguish which components that mixture contains. In homogeneous solutions they are known as solutions because their components have completely dissolved, while in heterogeneous solutions they have an uneven composition; in homogeneous solutions they have a uniform appearance, but in heterogeneous solutions they have an uneven appearance. In homogeneous mixtures we also see examples such as water with sugar, water with salt. In other words, I can't distinguish with the naked eye between vinegar dissolved in water and seawater. Ready? And in the heterogeneous one, we see the oil and water forming two layers. The sand, for example, yes, with the water, well, I see that it also cannot dissolve, and I can also observe the components that are part of that mixture. Okay, next. Let's look at the definitions in a moment. We're also going to leave you with the videos so you can watch them later and see in more detail what each of these methods consists of.

[01:19:00]So, for example, filtration.

[01:19:02]Filtration is a physical method that allows the separation of an insoluble solid from a liquid. Then, a filter is used that allows the liquid, called the filtrate, to pass through and retains the solid.

[01:19:17]For example, if we have water with sand, we can use that as a filtration method. The sand stays on the filter paper, as we can see in the image, and the water passes into the alerler container. Ready? So, if the question is in an example, guys, that they mention that it is a solid insoluble in a liquid, then we are going to use the filtration method. Let's move on to the next method, decantation.

[01:19:52]Decantation separates, or rather, separates heterogeneous mixtures using the difference in densities. We've also included a video here for you to watch later.

[01:20:05]Uh, this is used for solid- liquid mixtures, the solid settles, or in liquid-liquid mixtures when the liquids don't mix, like water and oil, which have different densities. So, for example, as we see in the image, the oil stays on top because it is less dense than the water, and this allows it to be separated by decantation. So, for example, if in a question, guys, they tell you, "I need to separate two liquids that have different densities, right? Or that have layers or are liquids that don't mix," then we're going to use the decantation method.

[01:20:47]And we'll move on to the last method, which is distillation. Distillation is used to separate homogeneous mixtures or liquids or solutions that, well, I mean, that I can't distinguish with the naked eye, right? And I'm going to separate them by the difference in boiling points.

[01:21:10]So, for example, water with salt: the water evaporates, then it condenses, and you get distilled water and salt.

[01:21:21]So, guys, when we're asked in a question that we need to separate a mixture using its boiling, evaporation, or condensation points, the answer is distillation, because distillation is the method based on boiling point, evaporation, and condensation.

[01:21:49]Let's move on to the next one. So, let's explore some questions to test our knowledge. Let's start with the first one.

[01:22:03]Based on what we've learned, indicate whether the following statement is true or false and justify your answer. I've already provided the answer here so you can check yours and be sure you're correct.

[01:22:19]According to Arenius, a base must produce OH ions when dissolved in water. This is true, since Arenius's definition of a base states that it is a substance that releases hydroxide ions when dissolved in water. Ready? Let's move on to the second statement.

[01:22:41]According to Browston and Lorry, for an acid to donate protons, the presence of a base capable of accepting them is not necessary.

[01:22:50]This is false, since the Browston-Lorry acid-base concept implies the existence of conjugate proton pairs. Remember when we discussed conjugate acids and bases? Therefore, for an acid to donate its protons, a base capable of accepting them is necessary. Let's move on to the next one.

[01:23:17]Indicate the conjugate acid of the following species when they act as a base in an aqueous medium.

[01:23:28]Since these species behave as bases in aqueous media, they accept a proton from water, generating the corresponding acids. For example, here we see the first ion, HCO3-. If it's in an aqueous medium, that means it reacts with water, forming H2CO3 + OH-. Ready? This means its conjugate acid is H2CO3.

[01:23:56]Let's move on to the second compound, which is water. When water reacts, its conjugate acid will be the hydroxide ion, as we studied in the first exercises. And the last one, the acetate ion, when it reacts with water, forms acetic acid plus hydroxide ions.

[01:24:17]Therefore, its conjugate acid is acetic acid. Ready? Here, we 're reacting it in an aqueous medium to find out its conjugate acid.

[01:24:30]Let's move on to the next one.

[01:24:37]A student mixes oil and Water, as shown in the image.

[01:24:43]Then, a separatory funnel is used to separate them. So, what are they telling me? Here, what is the basis for separating them? So, the difference in densities; the correct answer is B. We discard A because the boiling point corresponds to distillation.

[01:25:13]We discard C because oil and water do not dissolve in each other, and D because there is no chemical reaction.

[01:25:23]Therefore, to separate water and oil using a separatory method, the difference in density is used.

[01:25:37]Let's move on to the next one.

[01:25:42]The following table shows some physical properties of three substances. So, they are talking about water, sand, and salt. So, let's see what they are talking about in these tables.

[01:25:58]In class, the teacher mixes three substances and asks four students to explain how to separate the components of the mixture.

[01:26:08]The students' answers are shown below. So, we have Marta.

[01:26:13]Marta says, "It You must heat the mixture so that the water and salt evaporate, leaving the sand in the container.

[01:26:22]Enora, the mixture must be heated to evaporate the salt, then filtered so that the sand remains in the filter and the water can be obtained separately. Oscar, the mixture must be filtered so that the sand remains inside the filter, and then the water must be evaporated so that the salt remains inside the container. And Juan says, the mixture must be filtered, leaving the sand and salt inside the filter so that the water is separated. Ready?

[01:26:53]The correct answer is C, that is, Oscar. So, how do we identify it? So, first we must analyze the physical properties of the substances, that is, solubility, boiling point, density or state. Ready? First we identify what type of mixture it is and then we check what property allows its components to be separated. So, if there is an insoluble solid, we think about filtration. If there are liquids that do not mix due to different densities, we think of decantation. And if there are liquids that mix together or a solution with different boiling points, then we'll think about distillation.

[01:27:38]Therefore, this leads us to answer that the correct answer is C, Oscar's answer.

[01:27:46]Let's move on to the next one.

[01:27:54]Ready. With the next one. Then, he tells us, "Most modern cars are equipped with a catalytic converter.

[01:28:07]This converter makes the exhaust gases less harmful to people and the environment.

[01:28:18]Approximately 90% of the toxic gases are transformed into less harmful gases.

[01:28:25]Here we can see the gases entering and leaving a catalytic converter. The fact that carbon monoxide is transformed into carbon dioxide is a clear example that a reaction occurred.

[01:28:39]From this information, we can affirm that it occurred as a chemical reaction, a chemical change because there was a transformation of the substance.

[01:28:55]So, I can't say that there wasn't a change, that there was a change of state, no, because if they tell me that there was a reaction, there was a change in the nature of the substance.

[01:29:05]Therefore, according to the definition of physical and chemical change, this corresponds to a chemical change. Let's move on to the next one. Okay, we're almost finished.

[01:29:19]Let's move on to the next one. Expansion is the increase in volume that bodies experience when..." Contact with temperature. For example, the mercury in a thermometer expands easily, and that's why it's able to rise through a small capillary tube, indicating a rise in temperature. This phenomenon doesn't only affect liquids or solids, but also gases. When they receive an increase in heat, the particles separate from each other, allowing the gas to become lighter and more luminous. Therefore, one of the phenomena that explains the expansion of mercury is... let's get straight to the answer. The answer is D. Why? Because a physical change is generated by the activity of temperature, where what it does is expand the volume of the mercury. That is, not a chemical reaction. The only thing that happened was that, due to the increase in temperature, the volume also increased, that is, it expanded, and that's why I have that result of expansion. So that's what's happening in this exercise, a process of expansion. This is a physical change because there is no change in the nature of the mercury.

[01:30:38]Let's move on to the next one.

[01:30:45]This is An analysis of a graph. A student observes a graph showing how the amount of salt that dissolves in water varies at different temperatures. The graph shows that as the temperature increases, the amount of dissolved salt also increases. So, why does this happen?

[01:31:06]Well, as we were just saying, one of the factors that affects the solubility of a solute in a solvent is the increase in temperature. When we look at the graph where we have the solubility of the compound versus temperature, we see that at higher temperatures, the movement of the particles increases, also facilitating the dissolution or solubility of that solute in the solvent. So, temperature is one of the factors that also helps to accelerate this chemical reaction, as we can see or interpret it in a graph. Let's move on to the next one.

[01:31:51]Okay. This is the last one.

[01:31:54]Last question.

[01:31:56]A student performs the following experiment. They add salt little by little to 100 ml of water at a temperature of 25°C and observe the changes that occur in the solution. If the student heats the solution to 50ºC, what's most likely to happen?

[01:32:15]So, we were just talking about the effect of temperature.

[01:32:19]When the temperature increases, what happens? The solubility of that compound in water also increases. So, what's going to happen? That excess salt at the bottom could dissolve, reaching a new saturation point at that temperature in that solvent.

[01:32:38]So, remember, temperature is a factor that increases the solubility of a solute in a solvent. Ready?

[01:32:46]Let's move on to the next one.

[01:32:50]Let's wrap this up. Here's a brief summary of what we just covered so you can review it again. The topics we just studied: acids and bases, changes in matter, factors that affect dissolution, and methods of separating mixtures. So, this is an infographic that you can also review in much more detail. You can go back and study it, and there you'll find those basic concepts that will help you remember. The concepts we just studied. And to wrap up, we're going to have another final question. Remember that at the beginning of the session, we also started with a question that included a QR code so you could participate. Now we have a closing question. This question, based on what we've already studied and reviewed, will allow you to further solidify your knowledge. So, we invite you to click on this link, or Juan David will also leave it here online. It's already appearing here. And if not, you can also scan the QR code. We're already seeing responses here. Thank you so much, Isabela.

[01:34:19]Thank you very much. I see you've solidified the knowledge very well. I also invite anyone who wants to add their answers here; you're welcome to, because it was a very participatory and active session with you all. So, thank you very much for your attention and for the time you spent here.

[01:34:46]Participating during the session. We invite you to review the video again if you have any questions. We've provided plenty of material for you to review, including the infographic and the questions.

[01:34:59]This will help you solidify your knowledge and, of course, continue participating in the " Accompany Me" strategy classes so you can learn much more about these topics that the Ministry of Education is offering.

[01:35:16]Thank you very much, and have a wonderful day.