Now, ionic salts represent ionic compounds that are formed when an acid or base undergo a neutralization reaction. Here for our example, we have hydrochloric acid reacting with sodium hydroxide. When they react we're 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. In these series of videos, we're going to take a look at the steps necessary to determine if our ionic soda raw is acidic, basic, or neutral.
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concept
Ionic Salts - Cations
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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 3 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 plus 3 or higher to be acidic. Here we have 10 4 bromide. 10 4 bromide when it breaks up into ions produces 10 4 ion plus a bromide ion. Here we're not worrying about that it releases 4 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 plus 3 or higher, then it will be acidic. So this tin foil ion is acidic. For transition metals, they only need to be plus 2 or higher in order to be acidic. Here we have zinc chloride which breaks up into zinc 2+ion and the chloride ion. Zinc has met the minimum requirement of having at least a charge of plus 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, positive amines are weak acids. So, here a positive amine would be acidic. Here we have ammonium nitrate. It will 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 we'll 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.
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example
Ionic Salts Example
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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 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 plus 3 or higher. None of these ions meet that minimum requirement plus 3 charge, so none of them would 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 plus 2 or higher to be considered acidic. Manganese is 5+ 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.
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Problem
Problem
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
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concept
Cation Solubility
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Now recall that solubility is 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.
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example
Ionic Salts Example
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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 Remember transition metals need to be plus 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 is a group, a mangrove metal, they have to be plus 3 or higher in order to be acidic. Here it doesn't meet that minimum requirement so it's neutral. Next we have lead II ion, same thing. Lead II is a main group metal, it has to be at least plus 3 or higher to be acidic. Then finally here we have potassium, which is only plus 1 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.
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Ionic Salts - Anions
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Now in our exploration to understand ionic salts, we've now come to anions. 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 gonna 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 positive 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 its 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.
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example
Ionic Salts Example
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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 into chloride ion, nitrite ion, perchloride 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 gonna say here that hydrochloric acid, hydro, perchloric acid, hydrobromic acid, and hydroiodic acid all represent strong acids. That means since they're strong acid that means the negative ions, that it came from would be neutral. So all of these are neutral. Here we have nitrous acid, which is a weak acid. Since it's a weak acid that means its 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.
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Problem
Problem
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
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example
Ionic Salts Example
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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, so we're looking at the anion portion. So C3H503- For the anion, we add an H+ to it. When I add an H+ to it, I create a weak oxyacid. 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, basic anion, so solubility increases within the acidic solution. So here the answer would be option b.
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Problem
Problem
Which of the following compounds would have an increase in solubility when placed into an acidic solution?