Ionic Salts - Online Tutor, Practice Problems & Exam Prep

• Ionic salts are formed from neutralization reactions between acids and bases
• Ionic salts can be acidic, basic, or neutral
• Cations can be acidic or neutral based on their charge or identity
• Main group metals need a charge of +3 or higher to be acidic
• Transition metals only need a charge of +2 or higher to be acidic
• Positive amines are always acidic
• Solubility of acidic cations increases in basic solutions
• Anions can be basic or neutral based on their acceptance of a proton
• Adding H+ to an anion creates a weak or strong acid, determining if the anion is basic or neutral
• Weak acids create basic anions, strong acids create neutral anions

Ionic Salts

Now, ionic salts represent ionic compounds that are formed when an acid or base undergo a neutralization reaction. Here, for example, we have hydrochloric acid reacting with sodium hydroxide. When they react, we are going to create our ionic salt, which is basically sodium chloride aqueous and then we'll have water being formed as well.

Now this ionic salt of sodium chloride, we're going to say based on its identity, the salt can either be acidic, basic, or neutral. So in these series of videos, we're going to take a look at the steps necessary to determine if our ionic salt overall is acidic, basic, or neutral.

Ionic Salts - Cations

So remember that ionic salts are ionic compounds, and ionic compounds are composed of a positive ion called a cation and a negative ion called an anion. Here, let's first take a look at the cation rules. Here we're going to say cations can be either acidic or neutral based on the magnitude of their charges or their identity. So here we're going to break up cations into three groups. We have our main group metals, our transition metals, and our positively charged amines.

For main group metals, they have to have a charge of +3 or higher to be acidic. Here we have tin(IV) bromide. Tin(IV) bromide, when it breaks up into ions, produces a tin(IV) ion plus a bromide ion. Here we're not worrying about that it releases four bromide ions. We're just focused on the fact that a bromide ion appears because we've created a main group metal, a cation that has a charge of +3 or higher, then it will be acidic. So this tin(IV) ion is acidic.

For transition metals, they only need to be +2 or higher in order to be acidic. Here we have zinc chloride, which breaks up into a zinc 2+ ion and the chloride ion. Zinc has met the minimum requirement of having at least a charge of +2. Zinc would be an acidic cation.

And then finally, we're going to say that positive amines, which we've talked about before in other sections, are weak acids. So here a positive amine would be acidic. Here we have ammonium nitrate. It would break up into the ammonium ion plus the nitrate ion. Ammonium is our positively charged amine, and because it's a positively charged amine, it's automatically going to be acidic.

So remember in this section we're only looking at the positive ion, the cation. The negative ions will worry about them later on, but for right now, remember cations, we look at the main group metals, the transition metals, or if a positive amine is present. Knowing these rules will allow you to determine if that positive ion is acidic or neutral.

Ionic Salts Example

Which of the following reactions will create an acidic solution when dissolved in an aqueous solvent? So here we have these five choices. We're looking for an acidic solution, so we have to look and see what kind of cation we form. In the first one, we have sodium fluoride, so we produce NA. Plus here we have lithium acetate, so we're going to produce lithium plus. Here this is manganese 5 chloride, so we've create manganese 5 ion.

Strontium sulfide creates strontium ion and then calcium cyanide creates the calcium ion. Now we're going to say that sodium, lithium, strontium, and calcium, they're all main group metals. Remember, for the main group metal to be acidic, it has to have a charge of +3 or higher. None of these ions meet that minimum requirement of plus three charge, so none of them would be create an acidic solution. They all would be neutral here.

If we look at manganese 5, manganese is a transition metal. Transition metals only need to have a charge of +2 or higher to be considered acidic. Manganese is five plus what's definitely met that requirement. So here this could create an acidic solution when dissolved in an aqueous solvent.

Remember, we're looking to what creates an acidic solution, so we're looking at the cations that are formed in each of these compounds. So find the cation, the positively charged ion, and look at the magnitude of its charge to see if it can be acidic or neutral.

Which of the following compounds would decrease the pH of solution?

a) SrBr₂                         b) KSH                         c) NaN₃                         d) NiP                           e) Hg₂Cl₂

• A. SrBr₂
• B. KSH
• C. NaN₃
• D. NiP
• E. Hg₂Cl₂

Cation Solubility

Now recall that solubility as a chemical property that deals with the ability of a solute to become dissolved in a solvent. Here we're going to say for an acidic ion, the solubility increases when placed in a basic solution.

So now we're going to have to identify if a cation is acidic or neutral. The acidic ones will become more soluble. Within a basic solution, nothing will happen to the neutral ones.

So keep this in mind when we take a look at cation solubility.

Ionic Salts Example

Which of the following compounds will be the most soluble in a basic solution? So here we're wanting to take a look at the cations. When they dissolve, we're going to create this positive amine. Remember, positive amines are acidic. Since it's an acidic ion, its solubility will increase within a basic solution. So this would be an answer.

Next we have cobalt one. Remember, transition metals need to be 2 or higher in order to be acidic. This one does not meet that minimum requirement, so it is neutral. Next we have barium ion. Barium's a group on main group metal. They have to be 3 or higher in order to be acidic. Here it doesn't meet that minimum requirement, so it's neutral.

Next we have lead 2 ion. Same thing. Lead two is a main group metal. It has to be at least 3 or higher to be acidic. Then finally here we have potassium which is only plus one as a main group metal. So here the only cation that is acidic in nature would be the first one we produced a positively charged amine. Since it is an acidic ion, its solubility would increase within a basic solution. So here our answer is option A.

Ionic Salts - Anions

Now in our exploration to understand ionic salts, we've now come to an ions. Anions represent negatively charged ions. Anions can either be basic or neutral based on their acceptance of a proton. Now remember, a proton is just represented by an H ion. If we take a look here, we're going to say add an H to the anion. If a weak acid is created, then your anion is basic.

So if we take a look here, we have potassium fluoride, so it breaks up into K⁺ and F^-. F^- is our anion. We're going to add an H⁺ to it. When we do that, we create HF, which is hydrofluoric acid, which is a weak acid. That means that the fluoride ion is basic. That's because here we have a weak acid. If you're a weak acid, you're going to create a stronger conjugate base, just strong enough that it's classified as being basic.

Over here on this side, when we add an H⁺ to an anion, if a strong acid is created then the anion is neutral. Here we have sodium chloride which breaks up into sodium ion plus the chloride ion. Here we're going to add an H⁺ to the chloride ion to give us HCl hydrochloric acid, which is a strong acid. Because we created a strong acid, that means it's conjugate base is going to be extremely weak. So weak that we see it as being neutral. So this chloride ion here would be neutral.

So just remember when we have a negatively charged ion, add an H⁺ to it. If you create a weak acid then the negative ion is basic. If you create a strong acid, then the negative ion will be neutral.

Ionic Salts Example

Which of the following compounds will create a basic solution when dissolved in water? Here we're looking to create a basic solution, which means we need to look at the anion, the negative ion involved here. We're going to see that this breaks up in 2 fluoride ion, nitrite ion per chloride ion, bromide ion, and iodide ion.

To each of these we add an H plus to them, creating an acid. So here we're creating perchloric acid, hydrobromic acid, and hydroiodic acid. We're going to say here that hydrochloric acid, hydro umm, perchloric acid, hydrobromic acid, and hydroiodic acid all represent strong acids. That means since they're strong acid, that means the negative ions they came from would be neutral. So all of these are neutral.

Here we have nitrous acid which is a weak acid. So if it's a weak acid that means it's negative. Ion is basic. So this is the only basic anion that we have present and it will create a basic solution when dissolved in water. That means option B is our correct answer.

Which of the following compounds would increase the pH of solution?

a) SrBr₂                         b) K                              c) NaN₃                         d) NiBr₂                         e) Hg₂Cl₂

• A. SrBr₂
• B. K
• C. NaN₃
• D. NiBr₂
• E. Hg₂Cl₂

Ionic Salts Example

Here when it comes to the anion solubility, we're going to say that for the basic ion, the solubility increases when placed in an acidic solution. So here we're going to say what will happen to the solubility of the following ionic compound when it is placed in a solution with a pH of 4.0.

Well here the solution has a pH that is less than 7, so this represents an acidic solution. Here we break this up. We're looking to see if it's a basic ion. We're looking at the anion portion, so C3H5O3 -. For the anion, we add an H to it. When I add an H to it, I create a weak oxy acid.

Since I created a weak acid, that means that my negative ion will be basic. So this means that if I take this basic ion and I place it within the solution, it's going to cause the pH to increase to become more basic. So here what will happen to solubility of this compound? It is a basic anion, so its solubility increases within the acidic solution. So here the answer would be option B.

Which of the following compounds would have an increase in solubility when placed into an acidic solution? 

a) CaBr₂                                    b) NaI                           c) KCN                         d) LiNO₃                        e) Hg₂Br₂

• A. CaBr₂
• B. NaI
• C. KCN
• D. LiNO₃
• E. Hg₂Br₂