Was this helpful?
INSTRUCTOR: Solubility is the maximum amount of a substance that will dissolve in a given solvent, at a particular temperature. Solubility guidelines are put together based on experimental results. And they can be used whether to predict if a substance will be soluble or insoluble, or if we mix two solutions together, if a precipitate will form. To illustrate this, we have solid sodium carbonate. And we are going to dump it into a test tube of water. What will happen when I take solid sodium carbonate and dump it into this test tube containing water? As you can see, the sodium carbonate completely dissolved, which means it is soluble in water. How does this experimental observation relate to the solubility guidelines? In general, carbonates are insoluble. But important exceptions are NH4 plus and alkali metal cations. Because the sodium cation is an alkali metal cation, sodium carbonate will be soluble in water. If a solid is soluble, it will dissolve when we place it in solution. Now, let's take solid lead chloride and place it in a similar test to fill with water. What will happen when we take lead chloride and dump it into this test tube? As you can see, by this cloudy solution and the solid forming at the bottom of the test tube, the lead chloride did not dissolve, which means it is insoluble in water. Let's explore how this experimental observation fits in with the solubility guidelines. In general, chlorides are soluble. But important exceptions are compounds containing the silver cation, the lead 2 cation, and mercury 1 cation. If we repeated the same experiment with silver chloride or mercury 1 chloride, we would see that these compounds are insoluble. All other chlorides will dissolve in water or be classified as soluble. We can also use the solubility rules to predict whether a precipitate will form when two solutions are mixed together. In my right hand, I have a bottle of sodium sulfate, in my left hand, a bottle of potassium iodide. What will happen when we mix these two solutions together? As you can see, mixing the sodium sulfate and potassium iodide solutions did not lead to the formation of a precipitate. In order to think through this problem conceptually, let's analyze the two possible products of this reaction. Based on the results of our experiment, we would expect both potassium iodide and sodium sulfate to be soluble, meaning no precipitate will form. We can verify this by consulting the solubility guidelines. Sulfates and iodides containing alkali metal cations will both be soluble. Therefore, the solubility guidelines are consistent with our experimental observations. Now, let's try another example. In my right hand, I have a bottle of silver nitrate, in my left hand, a bottle of sodium carbonate. What will happen when I mix these two solutions together? We can see that when mixed together, these two solutions form a solid. But what exactly is this solid? And how do we properly express the products of this reaction? The reactants in this case are silver nitrate and sodium carbonate. We need to determine what this solid is and which ions are in solution. Each of these reactants are solutions. And we indicate an aq in parentheses to tell us that two solutions were mixed together. We now need to consult the solubility rules to determine what the solid product is. If we look at the solubility rules, silver carbonate is going to form and be insoluble or form this solid. We now need to balance the overall chemical reaction by putting a coefficient of 2 in front of the silver nitrate and also in front of the sodium nitrate. We can perform experiments like this for every combinations of solutions. But they are all summarized in the solubility guidelines. Being able to properly interpret these guidelines will allow you to predict whether an ionic compound is soluble or insoluble. And it will also allow you to predict the products of precipitation reactions.