In this module we're going to look at the solubility of ionic compounds. By the end of this module you should be able to identify whether or not an ionic compound is soluble or not based on the rules that we cover. First, we have to define what we mean by solubility. In that case, what we are looking at is when the maximum amount of solute that will dissolve in a given quantity of a solvent at a specific temperature. So that's the definition of solubility. And we declassify things as either soluble or insoluble. If it's something is soluble, then the majority of the solute dissolves. If something is insoluble, then the solute does not dissolve. Now there's a lot of gray area between, of things that are slightly soluble or somewhere in-between the soluble and insoluble. And we'll worry about those in another course. This time we're just looking at the kind of general definition of is it soluble or not. Now what we also know is that we've also said that ionic compounds are strong electrolytes, however not all of those compounds are soluble in water. So for those that do dissolve in water they can connect electricity. But any ionic compound that if its melted we're still going to get our ions and as a result it can conduct electricity. Which also makes it a strong electrolyte. What we want to determine here is which of those will be a strong electrolyte in water because they're able to dissolve in water. The first thing we're going to worry about are the solubility rules, determining which compounds are soluble. Whenever we see any of these ions, lithium, sodium, potassium, ammonium, nitrate, or acetate, we know that that compound is going to be soluble. So we don't have to worry about any other rules, any of these, it's going to be soluble. Likewise, when we see chloride, bromide, and iodine. These compounds are soluble, except when the cation is silver, mercury, or lead. So it's important to understand the rules but also the exceptions to those rules. Sulphates are also soluble. We have a few more exceptions here. Strontium, barium, lead, silver, and calcium are exceptions to that. For insoluble compounds remember, any time we see one of our lithium, sodium, potassium, or ammonium ions, we know that it's going to be soluble. Our exceptions on the hydroxide and sulfide are calcium, strontium, and barium. So what this says is that hydroxides are insoluble in water, except for calcium, strontium, and barium. And of course, lithium, sodium, potassium, and ammonium. These will trump all of our solubility rules. Likewise with sulphide, for carbonated phosphate, the only exceptions are going to be for lithium, sodium, potassium, and ammonium. Otherwise carbonate and phosphate compounds are insoluble. Now let's look at some examples and determine which of these compounds are soluble and which ones are insoluble. When I first look at lithium chloride I see that I have lithium, and I remember that any compound with lithium ions is going to be soluble. Next, I look at magnesium carbonate. Remember that carbonates are insoluble except when they're paired with lithium, sodium, potassium, or ammonium. Since it's magnesium this compound is insoluble. Sodium hydroxide. We see that sodium is there so automatically we know this compound is soluble. For sulfates, sulfate compounds are generally soluble however barium is one of our exceptions. So this is actually insoluble, and silver nitrate. We have NO3, which is one of our anions, that's always soluble and so silver nitrate is a soluble compound regardless of the solubility of silver compounds because the nitrate trumps any exceptions. Now we need to look at the change in solubility with temperature. We know the compounds are soluble. For example, if we look at sodium sulfate what we see is that we can look at the solubility of how it changes over time. We see that it has a decent amount of solute will dissolve in water. However, what we see is that things are temperature dependent. If I look at sodium chloride, I see that it starts around 37 grams per of solute, or 37 grams of sodium chloride per 100 grams of water. And as we increase the temperature, when we get to about 100 degrees celsius, we've only gone up to about 40 grams of NaCl per 100 grams of water. If I look at something like barium nitrate, notice it starts much lower, around five grams per 100 grams of water. But over time as the temperature rises I see that it goes up to 100 gram, 100 degree celsius and we have about 33 or 34 grams will dissolve in 100 grams of water. We notice that most of the substances increase their solubility with an increase in temperature. However there are exceptions. This is one of them that shows the solubility decreasing with an increase in temperature. In general, we see increases, but occasionally we do see decreases. So let's look at an example. Which of the following compounds is not soluble in water? So calcium carbonate is not soluble in water. For number one we see lithium is included in the compound, so we know that's soluble. Magnesium sulfate. Remember that sulfate compounds are soluble. Magnesium is not one of our exceptions so this compound is soluble. Potassium is one of our ions that always is a soluble compound. So we know this com, the potassium phosphate is soluble. Calcium carbonate. Carbonates are insoluble. Calcium is not one of the exceptions, so this is actually insoluble. And calcium carbonate is what's made of, in chalk, and so whenever you try to wipe chalk off a board, notice that you're just getting it stuck to a wet rag or wet paper towel, you're not actually dissolving that calcium carbonate in the water. The last one is strontium nitrate. And we know that all of our nitrate compounds are soluble. In the next module, we'll look at precipitation reactions.
