Ionic Salts of Weak Acids and Bases - Online Tutor, Practice Problems & Exam Prep

When an acid neutralizes a base, it forms an ionic compound known as a salt, which can be neutral, acidic, or basic based on the properties of its cations and anions. Cations can be classified as acidic or neutral, while anions can be basic or neutral. For example, F^- is a basic anion because it forms a weak acid (HF) when combined with H⁺. Amphoteric species can act as either acids or bases, depending on their environment, and include compounds like bisulfate and bicarbonate.

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-based 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 gonna say here, if they have a charge of plus 2 or higher, then they will be 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's from group 3a which explains where this 3 came from. It's Ga³⁺ plus the 3 iodides. Again, we're not focusing on the negative ion. 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. Finally, we have here positive amines. Now amines, remember, are compounds that contain carbon, nitrogen, and hydrogen. So like example, Methylamine or Benzylamine, or they're 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, It breaks up into the ammonium ion. This represents a positive amine because it contains just nitrogen and hydrogens. Remember, positive amines are automatically acidic.

Technically, here this NO₂ ^-, 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. So 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 +3 or higher to be acidic; because it is not, it is neutral. 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 bisulfate HSO₄^-, bisulfite, and dihydrogen phosphate. Here, these are all acidic types of amphoteric species.

For our basic ones, we have bicarbonate, we have hydrogen sulfide ion, and then we have hydrogen phosphate ion. 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 ionic salts and how are they formed?

Ionic salts are compounds formed when an acid neutralizes a base. This reaction results in the formation of an ionic compound, which consists of a cation (positive ion) and an anion (negative ion). For example, when hydrofluoric acid (HF) reacts with sodium hydroxide (NaOH), the products are sodium fluoride (NaF) and water (H₂O). The NaF is the ionic salt, composed of Na⁺ (cation) and F^- (anion). The properties of the resulting salt solution—whether it is neutral, acidic, or basic—depend on the acid-base characteristics of the cations and anions formed.

How can you determine if an anion is basic or neutral?

To determine if an anion is basic or neutral, you add an H⁺ ion to the anion and observe the resulting acid. If the resulting acid is weak, the anion is basic. For example, adding H⁺ to F^- forms HF, a weak acid, indicating that F^- is a basic anion. Conversely, if the resulting acid is strong, the anion is neutral. For instance, adding H⁺ to Br^- forms HBr, a strong acid, indicating that Br^- is a neutral anion.

What are amphoteric species and how do they behave?

Amphoteric species are compounds that can act as either acids or bases depending on their environment. They possess both hydrogen atoms, which allow them to donate protons (acting as acids), and negative charges, which allow them to accept protons (acting as bases). Examples of acidic amphoteric species include bisulfate (HSO₄^-) and dihydrogen phosphate (H₂PO₄^-). Basic amphoteric species include bicarbonate (HCO₃^-) and hydrogen sulfide ion (HS^-).

What determines whether a cation is acidic or neutral?

The acidity or neutrality of a cation is determined by its charge and type. Transition metals with a charge of +2 or higher are generally acidic. Main group metals need a charge of +3 or higher to be acidic; otherwise, they are neutral. For example, titanium(II) bromide (TiBr₂) dissociates into Ti²⁺ and Br^-. Since Ti²⁺ is a transition metal with a charge of +2, it is acidic. Conversely, sodium (Na⁺) from NaF is a main group metal with a charge less than +3, making it neutral.

How do you classify the solution of an ionic salt as acidic, basic, or neutral?

The classification of an ionic salt solution as acidic, basic, or neutral depends on the properties of its cations and anions. If the cation is acidic and the anion is neutral, the solution is acidic. If the cation is neutral and the anion is basic, the solution is basic. For example, NaF dissociates into Na⁺ (neutral) and F^- (basic), resulting in a basic solution. If both ions are neutral, the solution is neutral.