I honestly hate when we have to memorize a lot of things, polyatomic Ions is one and
this would be the second. Here we have to learn our solubility rules. Here we’re going
to say the solubility of a compound represents the maximum amount of solute you can dissolve
in the solvent. Solubility also has another name. Its other
name is concentration. And remember, we said that another name for concentration is molarity.
Solubility, concentration, molarity, all three of these terms are basically pointing at the
same thing. It’s talking about how much solute do we have in our solvent and together
what kind of solution forms? Now, what we should realize here is these
are our solubility rules. Now, here on the left side, we talk about soluble ionic compounds
and on the right, we talk about insoluble ionic compounds. Let’s go through this really
quickly just to see some of the basic types of ideas we have. Here we’re going to say
Group 1A ions, so Group 1A ions: H⁺, Li⁺, Cs⁺, Na⁺, K⁺ or ammonium which is a
polyatomic ion, when they’re connected to someone else, that compound will always be
soluble. For example, if I had NH₄ connected with
Cl. Soluble means when I throw it into water, it’s going to break up into ions. These
will break up into NH₄⁺ (aqueous) plus Cl⁻ (aqueous). It breaks up into the ions
that are present before we threw it into the water.
Nitrates, acetates, and remember acetate can be written in two forms, and most perchlorates
are soluble. Again, when these guys are connected to a compound, they’re going to be soluble.
If we have KClO₄, this breaks up into K⁺ plus ClO₄⁻.
Cl⁻, Br⁻, and I⁻ are soluble. Meaning they break up when they’re connected with
something else, except when they’re connected to silver, lead (II), copper (I) or mercury
(I), when they’re with these guys they stay as solids. We’re going to say that they’re
insoluble. Sulfates are soluble. Meaning they break up except when they’re with one of
these guys here. Now, insoluble ionic compounds basically means
that they’re solids. Another name for solid is precipitate. You’re going to hear these
words used interchangeably as well. Insoluble means it’s a solid. It doesn’t break up.
Solid also means precipitate. All three words are saying the same exact thing. OH⁻, S2-,
they’re insoluble except when they’re with Group 1A, ammonium, or one of these Group
2A ions. You can see how the things fit together. Of
course, they would be soluble with these guys because Group 1A ions are always soluble with
everyone. Ammonium is always soluble with anyone. Calcium, strontium and barium are
soluble with everyone except for sulfate. And then, carbonate and phosphate.Basically,
calcium, strontium, barium are insoluble with the -ates: sulfates, carbonates, phosphates.
Then we're going to say carbonates and phosphates are insoluble except when they’re with Group
1A or ammonium. There’s a lot of overlapping of trends. Your best strategy is just to remember
Group 1A elements and ammonium are soluble with everyone. Just remember that let’s
see the Group 2A ions, calcium, strontium, and barium are insoluble when they’re with
the –ates, so sulfate, carbonate, phosphate. Just remember these little tricks here and
there to help you remember what’s what. Other than that it’s really just memorizing
and it sucks, I know. But, you're going to have to do it to be able to do a lot of questions,
because they’re going to ask you to give us the formula when these two things mix together.
What are the products formed?