The first one to look at is the one in bold green in the next diagram. We'll look now at the phase diagram for sodium chloride solution in some detail. The solubility curve represents the boundary between these two different situations. If the temperature is below 57☌ for this mixture, you will have a mixture of two phases - the solution and some solid potassium nitrate. If you have a mixture of 100 g of potassium nitrate and 100 g of water and the temperature is above 57☌, you have a single phase - a solution of potassium nitrate. You can think of this as a simple phase diagram. The lower the temperature falls, the more potassium nitrate crystallizes, because the water will dissolve less and less of it. If the temperature falls even the tiniest bit below 57☌, the water will no longer dissolve as much potassium nitrate - and so some crystallises out. This is the temperature at which 100 g of water will dissolve 100 g of potassium nitrate to give a saturated solution. All the potassium nitrate will stay in solution.Īt 57☌, you hit the solubility curve. Now let the solution cool.Īt all temperatures above that marked on the graph (about 57☌), 100 g of water will dissolve more than 100 g of potassium nitrate. We'll take a solution containing 100 g of potassium nitrate and 100 g of water. For example, suppose you have a near-boiling solution of potassium nitrate in water. For phase diagram purposes, one important way of looking at this is to examine what happens if you decrease the temperature of a solution with some given concentration. Obviously, a solubility curve shows you the solubility of a substance at a particular temperature. For others (like sodium chloride), there is only a small change in solubility with temperature. For some (like potassium nitrate), the increase is quite fast. A solution is saturated if it will not dissolve any more of the salt at that particular temperature - in the presence of crystals of the salt.įor most, but not all, substances, solubility increases with temperature. The solubility is often (although not always) measured as the mass of salt which would saturate 100 grams of water at a particular temperature. \)Ī solubility curve shows how the solubility of a salt like sodium chloride or potassium nitrate varies with temperature.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |