Binary Acids - Video Tutorials & Practice Problems
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concept
Binary Acid Formation
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Hey everyone. So here we're going to say that binary acids represent covalent compounds containing the H+ ion bonded to a nonmetal anion not including oxygen. Okay. So binary acids are acids that do not possess oxygen within themselves. So if we took a look at 2 typical types of binary acids, let's look at H+ connecting to Br minus. Remember when the numbers are the same in terms of their charges, they just simply cancel out. So our acid here would be HBr, which is hydrobromic acid. And then here let's do H plus connecting to SH minus. Again, the numbers are the same. They just simply cancel out, so this becomes h two s. This is representing hydrogen sulfur hydrosulfuric acid. Right? So here we have 2 typical types of binary acids. So remember, when we're looking at a binary acid, it does not possess oxygen.
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example
Binary Acids Example
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Which of the following represents the possible structure of a binary acid? Remember, binary acid is an acid that does not contain oxygen. If we take a look at the first one we have a covalent compound beginning with the hydrogen. So yes, it is an acid but the presence of oxygen means it is not a binary acid. The next one isn't an acid at all, it's barium chloride. There's no H+ ions anywhere. The next one we have is HF. It's covalent. It starts with a hydrogen, so it's an acid. It has no oxygen, so it is a binary acid. This is hydrofluoric acid. Then finally we have LiH. Now here this is an ionic compound, and more importantly it is a metal cation connected to a basic anion. It is Li plus H-. This is an example of a base. Now if you didn't see that, make sure you go back and take a look at my videos where I talk about bases and the introduction of them. So here this would be a base. Out of all the choices, the only one that is a binary acid is option C.
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concept
Binary Acid Strength
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Now that we know how to identify binary acids, let's talk about their strengths. We're gonna say that our halo acids or halo acids, well, they're the only strong binary acids that exist and involve an H+ ion attached to a halogen. Remember, your halogens are your group 7a elements. And, the most important halogens on the periodic table are fluorine, chlorine, bromine, and iodine. Now, of these the strong binary acids are hydroiodic acid, hydrobromic acid, and hydrochloric acid. So those would be HI, HBR, and HCl, which would be these 3 here. Notice that I have not included Fluorine. That's because hydrofluoric acid represents a weak binary acid. We'll talk about that later on on why it's considered a weak binary acid and the other 3 are considered strong. Now, recall also that strong acids represent strong electrolytes, and weak electro weak acids represent weak electrolytes. We're going to say here that strong acids dissociate or ionize completely in water. And, we're gonna say that they donate a proton easily. When we say proton here we're talking about the H+ ion. We're gonna say that weak acids only partially dissociate or ionize. It donates a proton less readily, so not as easily, and it favors reactants, meaning it doesn't really want to break up into ions too much and rather stay in its molecular form. Here we have an example of hydrochloric acid and hydrocyanic acid. Both of these are binary acids. Hydrocyanic acid is one of our strong halo acids. It breaks up a 100% into H+ions and Cl-. To illustrate this, we use a solid arrow going forward. And we're going to say since it's a strong acid, it dissociates completely, which we see in the form of these 2 ions. It easily donates an H+. In reality, it's donating this H+ to the water that surrounds it. We'll see later on on how that works. And then, we are making a 100% of both of these ions. So basically, all of this is gone. The strong HCl is completely ionized. It's gone. It's all been transformed into the ions. So it favors the product side. For our weak acid, we have hydrocyanic acid, HCN. So if it's a weak acid we're gonna have the use of 2 arrows. We're going to have a larger arrow moving backwards and we're gonna have a smaller arrow moving forward. Okay. So you could show it like this or you could show it like this. Both are correct. And what this is showing me is that the larger arrow what's going which is going in reverse means that the reverse direction, the reactant side is more greatly favored. The smaller arrow moving forward means that very little of these 2 ions are produced, so we're going to have less h+cn- ions being produced. So HCN dissociates partially, meaning there's going to be more molecules of HCN than there are ions of H+cn- It less readily donates protons, so HCN doesn't easily give away an H+ to the water. And again, the larger arrow is pointing towards the reactant, so the reactant side is more greatly favored. So keep this in mind when we're talking about the strengths of binary acids.
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example
Binary Acids Example
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The following represent aqueous acid solutions. So identify the strong acid, the weak acid, and the weakest acid. So here we have as the general formula for or generic formula for an acid. Here when it breaks up it gives us H+ion and A minus ion. Here we're told that is in this form. H+ would be this smaller H+ion. A- will represent this larger, gold sphere. Now, if you are strong acid you completely ionize, you make a 100% of these 2 ions. So you should have none of this remaining. If we look at our options which one shows that? Well, if we look it's the middle one. The middle one we have only these 2, there is none of this hanging around. So, this represents our strong acid. The other 2 are weak because we have a lot more of the acid intact than we do ions being produced. But we have to identify which one is weak and which one is weakest. So if we take a look here, let's try to look at how many we have of each. We have 1, 2, 3, 4, 5, 6, 7. 7 of these HAs for the first one. And then how many h pluses do we have? We have 2h+2andthen2a-12. What about over here? Over here, we have 1, 2, 3, 4, 5, 6, 7, 8, 9. 9 HAs and only 1 H positive and 1 A minus. So we can see there's a lot more of the acid intact. So very little bit has broken up. So this would have to be our weakest acid Because it dissociates or ionizes the least. And then, this one will be a weak acid. So that's how we look at and depict each of these aqueous acid solutions. Remember, it all hinges on the fact that an acid, if it's strong, completely ionizes or dissociates into ions. A weak one only partially dissociates. The less it dissociates, the weaker the acid will be.
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concept
Comparing Binary Acid Strength
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Well, we know there are 3 strong binary acids, HI, HBr, and HCl. And we still need to know how to compare binary acid strengths nonetheless, because you could be asked to compare the strengths of 2 strong binary acids or to compare the strengths between weak binary acids. How exactly would we do that? Well, we're going to say here that the strength of binary acids is based on the electronegativity or atomic radius of the non hydrogen element. So here we take a look at a typical periodic table. We're looking at electronegativity, so as we go from left to right on the periodic table electronegativity, abbreviated en, would increase. And if we go down any group, we're going to say that atomic radius, abbreviated ar, would also increase. Okay. So these are the directions that allow these 2 periodic trends to increase. Now, how does this relate to the strength of binary acids? We're going to say here when comparing the strengths of binary acids, if the elements are in the same period or row, then use electronegativity electronegativity to compare their acid strengths. So here we're going to say, the greater the electronegativity of the non hydrogen element, then the more acidic the acid. If elements are in the same group or column, then use atomic radius in order to compare their acid strengths. Here we're going to say that the greater your atomic radius then the more acidic your acid. Right? So these are the concepts, periodic trends we're going to use to compare the strengths of different binary acids to one another.
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example
Binary Acids Example
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Which is the weakest acid from the following? So here we have HF, HCl, HI, HBR, or all or equal. If we look at the periodic table, remember we're looking at the non hydrogen element found within the binary acid. So we need to compare fluorine, chlorine, bromine, and iodine to one another. When they're in the same group, remember when you look at atomic radius. And when you say the higher the atomic radius then the more acidic the acid. If we look, iodine would have the largest atomic radius out of the 4 elements. As a result of this, HI would be the strongest acid, but here we're looking for the weakest. The one with the smallest atomic radius would be Fluorine, so HF would be our weakest acid. So here option a is the correct answer.
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example
Binary Acids Example
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Now, there will come times when we're comparing binary acids and they're not found within the same period or row, or not found within the same group or column. So what exactly do we do? Well, we're going to say that if the binary acids are separated by 1 period, then use electronegativity to compare their acid strengths. If separated by more than 1 period, then use atomic radius to compare their acid strengths. If we take a look here at this example question, it says, which is the weakest acid from the following? We have H2SC, HF, H2TE, H2S or they're all equal. We have to look at the non hydrogen element of the binary acid, so we are comparing Selenium, Fluorine, Tellurium, and Sulfur. We want the weakest acid here. Alright. So, if we take a look, we're going to say that sulfur, selenium, and tellurium are all within the same group. Since they're all within the same group we look at atomic radius The larger the atomic radius, the stronger the binary acid. So h two t e would be stronger than h two s e, H2S E would be stronger than H2S, so these 2 are out. Since they're both stronger than H2S we know that they couldn't be the weakest acid. So that means we now have to compare HF versus H two S. So how do we determine which one is weaker? Well, we're gonna say here if binary acids are separated by 1 period then we look when we use electronegativity to compare their acid strengths. Fluorine is in the 2nd period, sulfur is in the 3rd period. They're only separated by one period from one another. If we look at electronegativity, fluorine is more electronegative than sulfur. Chlorine is the most electronegative element on the periodic table, So that would mean that HF is more acidic than H2S. So by process of elimination, option d would be the best answer. It is the weakest acid out of all the options given.
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Problem
Problem
Which of the following acids would be classified as the strongest?