Chemistry

Introduction to Acid and Base Concepts



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Are you having trouble understanding the fundamental concept of acid base chemistry? Yes? Well, are you truly thinking at the high school or college level? Yes? Well, see, that's your problem right there! Stop it! You need to get in the five-year-old state of mind.

Say you have a ball, and I have a glove. You throw me the ball, and I catch it. You used to have that ball. Now you don't. I didn't have that ball. Now I do. Got it? Now you understand Bronsted-Lowery acids and bases.

A Bronsted-Lowery acid is the guy with the ball, and the "ball" is a hydrogen ion, more commonly called a proton. Anything that has the ability to "donate a proton", i.e. "throw the ball" can act as a Bronsted-Lowery acid.

A Bronsted-Lowery base is the gal with the glove. Anything that can "accept a proton", i.e. "catch the ball", can act as a Bronsted-Lowery base.

Hence, an acid/base reaction (by the Bronsted-Lowery definition) is simply a game of catch between two molecules. The one that throws is the acid. The one that catches is the base. It's that simple.

Now, as you're probably thinking, a game of catch can go both ways! So can an acid base reaction. If you start with the ball (and are hence the acid), and I start without it (being the base), we reverse roles once you toss and I catch. Now I become an acid, since I have the ball, and you're a base since you don't.

Chemists use the terms "conjugate acid" and "conjugate base" for the products of the acid base reaction. Since I started out as a base and became an acid only when you tossed me the ball, I am now the "conjugate acid". Adding the work "conjugate" just means that I'm an acid now, but before the reaction, I was a base. Since you started out as an acid and became a base when you tossed me the proton/ball, you are now the "conjugate base". Again, adding the word "conjugate" means that you are a base now, but you started as an acid.

As molecules toss the proton back and forth, they switch from acid to base and back again many, many times. Now, as anyone who has played catch knows, some people are "ball hogs". If I tend to hang onto the ball for a while and won't throw it back to you very quickly, than I'm a relatively strong base. Yes, we're tossing the ball back and forth, but I really like catching and holding that ball, so it spends more time in my hands than in yours. Because I like accepting that proton/ball, I am more "basic", since a base is a proton acceptor.

You, on the other hand, may toss that ball like it's a hot potato. You don't want to hold onto it. You would rather just toss that proton/ball to me as soon as you catch it. That makes you a relatively strong acid. An acid is a "proton donor" and you like to "donate" that proton/ball much more than you like to "accept" it. Molecules that would rather give up a proton are stronger acids, and molecules that would rather accept one are stronger bases.

Some things to keep in mind:

1. Initially, you may learn that there are "strong" and "weak" acids. That's kind of like saying there are "tall" and "short" people; in other words, it's pretty silly. Acids vary in strength just like people vary in height. Also, just like a medium height person looks short in comparison to a very tall person, a medium strength acid will seem weak in comparison to a much stronger acid. The same holds for bases.

2. Lewis acid/base theory has different definitions and is more versatile. The ball analogy words best for the Bronsted-Lowery definition. Lewis acid/base theory is vital for organic chemistry.

3. Inorganic chemists use yet another acid/base definition in order to explain single electron transfers in terms of acids and bases.

4. Teachers- seriously, take a ball and write H+ on it. Have the kids toss it back and forth. It will help.

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