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Naming Acids - Concept

Teacher/Instructor Jacqueline Spivey
Jacqueline Spivey

Ph.D.,U.C.Santa Cruz
Teaching at a top-ranked high school in SF

She teaches general and chemistry at a top-ranked high school in San Francisco. Prior to that, she lead and published a number of research studies and lectured at SF State University.

When naming acids, there are several guidelines that must be followed. The rule for naming acids depends on whether the anion contains oxygen. If the anion does not contain oxygen, acid is named with prefix hydro- and suffix -ic to the root of element. If the anion does contain oxygen, the name is formed from root name of central element of anion or anion name, with a suffix of -ic or -ous. When anion name ends in -ate, the suffix -ic is used.

So this segment let's go ahead and talk about how to name acids. So right after that I'll go ahead and say that I've been a Chemist for quite a long time, so I just kind of have an understanding of how to do acids. What I'm going to show you here are the basic rules for knowing how to do it and over time it will become more of second nature to you but in the meantime it's just going to have to be become something that you memorize. So I'll give you a few examples here and then you're going to want to go back and do them a few times and do a few different ones so that you can get your level of comfort up.

So let's recall that acids produce proton ions when dissolved in water. So H+ ions and that an acid can be thought of as a molecule with one or more H+ ions attached to an anion. And so basically, then when we're talking about the rules for naming acids, it's going to depend on whether or not the anion contains oxygen. So that's kind of a good trigger point. Remember that whether or not the anion contains oxygen will help you to remember how to name your acid. So let's go with the first rule.

So if the anion does not contain oxygen then the acid is named with the prefix hydro and the suffix ic attached to the root of the element. So the one example I have here is H2S which is dihydrogen sulphide and so when we dissolve it in water, then we'll get the acidic form of that and it will be named hydro for the prefix and then the root, right, is sulphur and then the ic on the end. So we get hydrosulphuric acid from H2S.

So the second rule is that when your anion contains oxygen, the acid name is formed from the root of the central element of the anion or the anion name with the suffix of ic or ous. So let's distinguish between whether or not you get the ic or whether or not you get the ous. So when the anion name ends in ate, then you get the suffix ic. So a couple of examples. H2SO4. So the anion of H2SO4 is SO4 2-. A quick recall here is you might be wondering how I remembered that SO4 is a 2-, has a 2- charge. Well, I know for sure that H has a +1 charge and there are two of them. So that means that SO4 must have a 2- charge. It's the simple way to remember if you don't always remember the charges on your polyatomic anions. Okay. So this sulphate ion is the anion of H2SO4. So, and it ends in ate, so that means we are going to replace it with ic once it becomes an acid. So H2SO4 is sulphuric acid.

We also have HNO3 for which the anion is NO3-. Again here I have one proton, so that means that the charge of my polyatomic must be -1. To get an overall zero charge. So nitrate. Here for the anion will turn into nitric acid, with the ic ending. Another quick thing since we're still talking about acids that you'll remember is that H2SO4 is a diprodic acid. It can lose two protons in solution versus HNO3 is a monoprodic acid. Just a quick aside.

So, the last part of this rule is that when your anion name ends in ite, the suffix ous is used. So a couple of examples. H2SO3 for which the anion is SO3 2-. We name that sulphite. So then the acidic form of H2SO3 is sulphurous acid. And then last but not least here. HClO, this is a chlorine and one oxygen which has the anion of ClO- which is a hypochlorite and so that would give us hypochlorous acid. So within this naming of acids, there are about 10 or 15 pretty common strong acids that you'll probably nee dto know and understand how to name. And I encourage you to look those up and work on that skill.

And that's naming acids.