Protic Acids and Bases - Online Tutor, Practice Problems & Exam Prep

Acids are classified into two main types: binary acids, which consist of H⁺ and a nonmetal without oxygen, and oxyacids, which include H⁺, a nonmetal, and oxygen. Binary acids, like HF and HCl, often form from halogens, while oxyacids, such as phosphoric acid (H₃PO₄), arise from the hydration of nonmetal oxides. When acids neutralize bases, they produce salts, which can be acidic, basic, or neutral based on the properties of their cations and anions. Understanding these classifications aids in predicting acid-base reactions and their outcomes.

Acid Identification

Here we're going to say that the most common feature of an acid is that many possess an H⁺ ion. This ion can be called the hydrogen ion or the hydronium ion. Now, we're going to say here when it comes to acids, there are basically 2 major types that exist. Here we're going to talk about the first one. Here we have binary acids. Binary acids where we have H plus connected to an electronegative element. Now, here we're going to say that these types of acids lack the element oxygen and they usually possess no metals. The most common type of these types of particular acids are the halo acids. From the name, we can tell that they're connected to halogens. Here we have HF, HCl, HBr, and HI. Basically, in order to make them, so these are from group 7, we have H⁺ and remember, group 7A elements, they all have a charge of minus 1. Just 1. So basically, that's how we got these halo acids. Now other types of binary acids that can occur as well, group 6. So we have S₂ minus, Se₂ minus, Te₂ minus. They also can combine with H⁺ to give us binary acids. So here, the numbers are different within the charges, so they don't cancel out like the halo acids. They crisscross. This is H₂S, which is hydrosulfuric acid, hydroselenic acid, hydrotelluric acid. These are some of the most common types of halo acids that exist. We also have other ones such as hydrocyanic acid. And then here you can have hydroazacic acid or azoic acid. These are most common types of binary acids that can exist. Just realize here that when it comes to binary acids, you basically have an H⁺ in front connected to a nonmetal that is not common. In the next video, you'll be able to see the second type of acids that are most common. So just click over to the next video and take a look at the second class of acids.

Acid Identification

Our second class of acids are known as oxyacids. Oxyacids consist of H⁺, a nonmetal, and oxygen. These components usually form a polyatomic ion that interacts with the H⁺. For example, combining H⁺ with the phosphate ion results in H3PO4, known as phosphoric acid, an example of an oxyacid. When H⁺ combines with the nitrate ion, it creates nitric acid. These ions interact to form acids, but in reality, they are often created by the hydration of non-metal oxides.

To form carbonic acid, carbon dioxide gas reacts with water. This also explains why leaving tap water out in a glass will cause it to become slightly acidic over time, as carbon dioxide from the atmosphere dissolves into it. Similarly, the formation of sulfuric acid involves the reaction of sulfur trioxide gas with water. This illustrates the creation of oxyacids, which are simply H⁺ combined with a nonmetal and oxygen. Identifying these three components helps in recognizing oxyacids.

Acids fall into either the binary acid model or the oxyacid model. Understanding these two types of acids is crucial. Moreover, acids and bases exhibit polarity, which facilitates their interaction in aqueous solutions through the donation or acceptance of H⁺ ions. When studying acids like oxyacids and binary acids, remember that their polarity is essential for predicting their behavior in solutions.

Now that we understand the two types of acids, let's apply this knowledge to solve the problem below. Reflect on how acids and bases use polarity in interactions and use this understanding to guide you to the correct answer. Review how I approach and solve the same question.

Acid Identification

So here it states, which of the following compound or compounds cannot be classified as an acid? Recall that we said acids fall into 2 categories. We have our binary acids and our oxyacids. And both types of acids contain some level of polarity. Now, if we take a look at the first one, we have H2Se. That's one of the examples we saw for a binary acid. That is hydroselinic acid. It is an acid, so that is out. Next, we have HOCN. We have hydrogen, oxygen, and some nonmetals. That there represents an oxyacid. In fact, this is cyanic acid. Next, we have HN3. That is also a binary acid we saw above. So this is hydro azide acid. Next, we have C3H8. This compound here is composed of only carbons and hydrogens. So it is, by nature, nonpolar. Remember, the electronegative difference between carbon and hydrogen is very minimal. So small in fact that we say it contains nonpolar bonds. This is a nonpolar compound therefore it cannot represent an acid. Here out of all the options, choice d would have to be the correct choice. Remember, when it comes to these types of acids, we have binary acids which are just H plus connected to an electronegative element. Those electronegative elements, the most common ones, are nitrogen, phosphorus, sulfur, or one of the halogens like selenium or tellurium. Remember, binary acids do not contain oxygen and they usually possess no metals. Oxyacids are H plus connected to a nonmetal and oxygen. The nonmetal and oxygen really just form a polyatomic ion that is connected to that H⁺ ion. Remember these fundamentals when trying to describe the different types of acids that exist.

Ionic Salts

Here we're going to say that when an acid neutralizes a base, an ionic compound called a salt is formed. These solutions can be neutral, acidic or basic depending on the acid-base properties of the cations and anions formed. So a good example here, we could have HF reacting with NaOH. So the compounds that we make are NaF plus water. NaF represents my ionic compound. That is my ionic salt. Now this ionic salt is composed of a cation which is a positive ion and an anion which is the negative ion. We'll come back to this later on and see what kind of solution this ionic salt could potentially make. Now when we're taking a look at the ions, remember we have cations and anions. Cations are just the positive ions and we group them into 3 major categories. We have here our transition metals, our main group metals, and our positive amines.

Now here when it comes to transition metals, remember on your periodic table, those are the metals within the pit of the periodic table. We're acidic. If their charge is less than plus 2, then they are classified as being acidic. If their charge is less than plus 2, then they are classified as neutral. Here, we have titanium 2 bromide. When it breaks up into its ions, it breaks up into titanium +2 and Br−. Again, we're only focusing on the positive ion for this point. Here, this is a transition metal. It's met the requirement of having a minimal charge of 2+. Because of that, this titanium ion is acidic. Next, main group metals. These are metals from groups 1a, 2a, 3a, 4a, basically metals that are not transition metals. For them, they have to be plus 3 or higher in charge in order to be acidic. If they are less than plus 3, then they are neutral. Here we have gallium iodide. Gallium is from group 3a which cation, the positive ion that is At this point, we're just focused on the cation, the positive ion that is formed. Here, gallium has met the requirement of having a plus 3 charge or higher. Therefore, it is acidic. For our first two examples, this would help to create an acidic solution so with this.

Finally, we have here positive amines. Amines, remember, are compounds that contain carbon, nitrogen, and hydrogen. So like example, Methylamine or Benzylamine or their compounds that contain just nitrogen and hydrogen, like ammonia or the ammonium ion or hydrazine. Now, we're talking about the positively charged ones. Here, positively charged amines are acidic. Here, we have ammonium nitrate, so it breaks up into the ammonium ion. This represents a positive amine because it contains just hydrogens. And remember, positive amines are automatically acidic. Technically, here, this NH₂ minus would be basic. But again, we're just focusing on the positive ion for this portion. Remember, an ionic salt deals with an ionic compound which is composed of a positive ion called a cation and a negative ion called an anion. At this point, we've looked at the requirements to determine if a positive ion is either acidic or neutral.

Click on to the next video and see how do we gauge if an anion, which is the negative ion, is acidic, is basic or neutral. So anions can either be basic or neutral. And cations can be either acidic or neutral. So keep in mind the rules that we've covered in terms of a cation. Click on to the next video to take a look at anions.

Ionic Salts

So now we're going to take a look at anions. Remember, anions are your negative ions within your ionic salt. They can either be basic or neutral. Now here we're going to say, if we take a look at KF, it breaks up into K⁺ and F^-. We're going to say here to determine if this is a basic ionic salt, we're going to add an H⁺ to the negative ion. So we add H⁺ to F^- to give us HF. We're going to say add an H⁺ to the anion and if you create a weak acid then your negative ion is basic. Here, HF is a weak acid and because it's weak that means its conjugate base will be stronger. F^- is stronger so we can say it's basic. Now here we have LiBr. So we break this up into its ions. Again, we add an H⁺ to the negative ion. But in this case, if you create a strong acid, which this is, that means that your conjugate base, the Br^-, is neutral. Remember, if you're strong one way, you're incredibly weak the other way. If you create a weak acid, that means you have a stronger conjugate base. That's why it is basic. If you create a strong acid, that means you have an incredibly weak conjugate base. So weak that it is neutral. That's how we take a look at an ionic compound. Here, if we were to go back up to our NaF that we got originally, we have Na⁺ which is a cation. It is a main group metal. Remember, they have to be plus 3 or higher to be acidic. Because it is not, it is neutral. F^-, we just saw that if you have a negative ion, you add an H⁺ to it. We create HF which is a weak acid. This negative ion is basic. When you have a neutral and you have a basic, that means your solution overall will be basic because neutral means we can ignore it. We'd say that NaF is a basic ionic salt. Now that you've seen cations and anions, click on to the next video to take a look at amphoteric species.

Ionic Salts

So amphoteric species are compounds that can act as an acid or a base. Now when it comes to amphoteric species, they can be classified as being either acidic or basic. In this category, it's just important to remember which one we put in whichever category. Now when it comes to acidic amphoteric compounds, remember what fits in this category are we have bisulfate, HSO₄^-. We have bisulfite, HSO₃^-. We have dihydrogen phosphate, H₂PO₄^-. Here, these are all acidic types of amphoteric species.

For our basic ones, we have bicarbonate, HCO₃^-. We have hydrogen sulfide ion, HS^- and then we have hydrogen phosphate ion, HPO₄^2-. Again, remember, an amphoteric species can act as an acid or a base. This is seen by the fact that they possess hydrogens, so they can act as acids, but they also possess negative charges so they can act as bases. But here, their grouping is really based on their Ka values. Later when we take a look at diprotic as well as polyprotic acids and bases, we'll learn why exactly we classify some as acidic and others as basic.

Here’s what students ask on this topic:

What are the main differences between binary acids and oxyacids?

Binary acids consist of hydrogen (H⁺) and a nonmetal without oxygen. Examples include HF, HCl, and H₂S. Oxyacids, on the other hand, contain hydrogen (H⁺), a nonmetal, and oxygen. Examples include H₃PO₄ (phosphoric acid) and HNO₃ (nitric acid). Binary acids typically form from halogens or group 6 elements, while oxyacids arise from the hydration of nonmetal oxides. Understanding these differences helps in predicting their chemical behavior and reactions.

How do you determine if an ionic salt is acidic, basic, or neutral?

To determine if an ionic salt is acidic, basic, or neutral, examine the properties of its cations and anions. Cations can be acidic or neutral, while anions can be basic or neutral. For example, if the cation is a transition metal with a charge of +2 or higher, it is acidic. If the anion forms a weak acid when combined with H⁺, it is basic. The overall nature of the salt depends on the combination of these properties. For instance, NaF is basic because Na⁺ is neutral and F⁻ is basic.

What are amphoteric species and how are they classified?

Amphoteric species are compounds that can act as either an acid or a base. They possess both hydrogen atoms and negative charges, allowing them to donate or accept protons. Examples of acidic amphoteric species include HSO₄⁻ (bisulfate) and H₂PO₄⁻ (dihydrogen phosphate). Basic amphoteric species include HCO₃⁻ (bicarbonate) and HPO₄²⁻ (hydrogen phosphate). Their classification is based on their acid dissociation constants (K_a values).

How are oxyacids formed from nonmetal oxides?

Oxyacids are formed by the hydration of nonmetal oxides. For example, carbon dioxide (CO₂) reacts with water (H₂O) to form carbonic acid (H₂CO₃). Similarly, sulfur trioxide (SO₃) reacts with water to form sulfuric acid (H₂SO₄). This process explains why water exposed to air becomes slightly acidic, as CO₂ from the atmosphere dissolves in it.

What happens when an acid neutralizes a base?

When an acid neutralizes a base, they react to form an ionic compound called a salt and water. For example, HF (hydrofluoric acid) reacts with NaOH (sodium hydroxide) to produce NaF (sodium fluoride) and water (H₂O). The resulting salt can be acidic, basic, or neutral depending on the properties of the cations and anions formed during the reaction.