If you're taking a beginning course in chemistry, you may be required to memorize some or all of the important solubility rules. These rules will help you predict which ionic compounds dissolve in water and which will not. Teachers are unlikely to ask questions that require you to restate the solubility rules -- they're more likely to ask questions that require you to use these rules. For example, a quiz might have a question like, "Which of the following reactions will form a precipitate?" The following explains some tricks and tips for memorizing these rules successfully.
Create a mnemonic to help you remember which compounds are soluble. One possible example is as follows: "Not All Attractive Fun Cheerleaders Buy Indecent Skirts", where the first letter of each word stands for a class of compounds that are generally soluble (N = nitrates, A = acetates, A = ammonium, F = fluorides, C = chlorides, B = bromides, I = iodides, S = sulfates). Several of these groups have exceptions, however, so you'll need to either remember the exceptions or create a mnemonic for those exceptions. For example, chlorides are all soluble except for compounds with mercury, silver or lead, so you could use the first letter of each name (or the first letter of the symbol, e.g. HAP) to come up with a short three-word sentence that will help you remember them.
Remember the solubility of different elements by their position on the periodic table. Any compound with an element from group 1 is soluble, and any compound with an element from group 17 is soluble unless it's partnered with mercury, silver or lead (all of which are fairly close together on the periodic table) or (in the case of fluorine only) if it's partnered with strontium and barium, both of which are in group 2 of the periodic table. Since you will almost invariably have a periodic table available while you are working on a chemistry exam, if you can remember what dissolves and what does not based on its position on the periodic table, you should have no problems on a test.
Try composing a song or poem to help put the solubility rules in an order that will make them easy to remember. One possible example is listed under the Resources section and can be sung to the tune of "99 Bottles". You can't sing the song out loud during an exam, but you can always sing it to yourself silently.
Try writing the solubility rules (or just a list of soluble compounds and exceptions) over and over until you know them without looking at your book. Always write or repeat them in the same order -- this will help you keep them organized in your mind.
Learn to recognize common exceptions like mercury, lead and silver compounds with halogens -- these will all be insoluble. If you spot one of these exceptions, it will help you to rule out some of your possible options on a multiple-choice question.
- Chad Baker/Ryan McVay/Photodisc/Getty Images