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Integrated Science 1B Part 1
Integrated Science 1B Part 2
Period 2 - ISB
Period 3 - ISB
Period 4 - Honors Chem
Period 5 - Adv Chem
Acids and Bases
Acids and bases are kinds of chemicals that can be said to be opposites of each other. This means that acids will react with bases, but probably not with other acids. Acids are commonly seen in media, especially in movies and cartoons, but bases are equally important in the world. There are lots of misconceptions about acids and bases and this article will try to clear some of them up.
Arrhenius Acids and Bases
One definition of acids and bases was made by a man named Arrhenius (pronounced: are-ree-knee-us). He defined an acid to be anything that dissolves in water and releases hydrogen ions:
Remember, an ion is a charged particle. When certain chemicals, mostly ionic compounds, dissolve in water, they stop being molecules and instead become ions floating around in the water. Arrhenius said that acids were compounds that released hydrogen ions. This is a good definition for many acids and it is what we will use in this class, but it isn't complete and we'll see why after we talk about bases.
Arrhenius said that a base is a compound that dissolves in water and releases hydroxide ions:
Remember, the hydroxide ion is a polyatomic ion and must be looked up on a special table. Since bases are the chemical opposite of acids, this definition makes a lot of sense, especially when you put an acid and a base together:
HA + BOH
AB + H
You can see here that acids and bases react to form a new compound, called a salt, and water. If done perfectly, this new solution will be perfectly neutral and not be acidic or basic. Now you can see why acids and bases are opposites--each one contains one half of water. This defintion works very well for many acids and bases, especially ones you find around your house, but it isn't completely right. After all, ammonia is a base, but it doesn't release any hydroxide ions in water. Strange...
Lewis Acids and Bases
A more complete definition of acids and bases was given by a great chemist named Lewis. You may have heard of him from Lewis dot diagrams. He said an acid is a compound that can accept a pair of electrons from another compound, and a base is a compound that can donate a pair of electrons. To understand this, you need to look back at electron configurations and remember that elements contain electrons that are either paired or unpaired, and that all elements really want to have all electrons paired up in order to be stable. Here's how it works:
Hydrogen normally has one electron, but to become stable it loses that electron and becomes a cation. Now it has no electrons and it is considered 'empty' by other chemicals. This means that a hydrogen ion could accept a pair of electrons from another chemical to share. So all acids that release a hydrogen ion can accept a pair of electrons. A good way to remember this is: Acids Accept.
Ammonia is a base and is made up of one nitrogen and three hydrogen atoms. In this arrangement, nitrogen has a pair of electrons that aren't being used to bond to the hydrogen, therefore it can donate or loan these electrons to another atom. Because it can donate these, that makes it a base. But wait a moment, how do hydroxide ions fit in? Well, the oxygen atoms on a hydroxide ion has lots of electrons that are paired up. This means that it can very easily donate a pair of electrons to share with another atom. Because of this, most hydroxide bases are considered to be 'strong' and many nitrogen bases are considered 'weak'.
Strong and Weak
Strong and weak are two different types of acids and bases. Strong acids/bases will completely separate into ions when they dissolve in water. This process is called
and it means that a compound separates into ions. It is different from dissolving in that a compound can dissolve in water, meaning that it can mix completely, but it doesn't always have to separate into ions. If an acid or base doesn't completely dissociate, or separate into ions, it is called a weak acid or base. When we talk about acids, strong acids include hydrochloric and sulfuric acids. Some weak acids include carbonic acid, vinegar (acetic acid), and citric acid. Strong bases include lye and Drano while weak bases include many cleaning products such as bleach and ammonia.
Does this mean that all strong acids are stronger than weak acids? Not at all, but we have to define what we mean by strength. One meaning of strength could be that an acid or base reacts with lots of things and does so very well. Acids commonly eat through metal, so a strong acid might eat through more metals than a weak acid. In this meaning of strength, strong acids/bases are almost always stronger than the weak acids/bases. But there is another way to look at strength and that is called concentration.
As you learned in the unit on reaction rates, the concentration can affect the speed or rate of a chemical reaction. This also goes for acids and bases as well. A more concentrated base will react faster than a more dilute base. Does this mean that if you took a weak base and made it very concentrated that it would be stronger than a very dilute strong base? The answer is yes, within some limits. A concentrated weak base still cannot react with things that a strong base could, but when it comes to the things that it does react with, it will do so better and faster than the strong base. Sometimes we say that means that the concentrated stuff is stronger than the dilute stuff. That isn't wrong, but remember that there are two kinds of strength.
Most people think that acids are worse and more dangerous than bases. After all, in the movies acids can eat through anything while bases are almost never seen (and they certainly aren't explained at all). In reality, bases are just as dangerous as acids. Acids can cause very painful burns and they can eat through metal and the enamel on your teeth. Bases can't eat through metal (most of the time), but they can dissolve your skin and organs. Acids hurt you by tearing apart certain chemicals inside your cells and causing damage to vulnerable spots, rather like stabbing a cake with a knife over and over again. Bases hurt you by reacting with fats in your cells and turning them into soap, dissolving them away. Imagine putting a piece of cake under the faucet and watching it gently wash away.
If you spill an acid or a base, you need to do two things quickly. First you need to get rid of the stuff on you. You can do that by rinsing yourself with lots of water. Hold the area under the faucet (or hose) for 20 seconds for small spills, and more for larger ones. The second thing you need to do is to neutralize the chemical. Earlier we said that acids and bases react to make water. This process is called neutralization. So if you spill an acid, you need to use a base to help clean it up, and if you spill a base you should use an acid. Since you don't want to burn yourself a second time, use a weak acid/base to clean up instead of a strong acid/base, and make sure it isn't too concentrated. Base spills are handled well with vinegar or cream of tartar and acid spills are handled best with baking soda. Make a paste or use a paper towel to scrub yourself to get rid of any leftover chemical. Make sure to do this after you rinse with water because the reaction can get hot sometimes and you don't want to give yourself another burn.
For clothes and things like counters and floors, you should try and rinse the area as best you can before applying the vinegar or baking soda. If you can't use lots of water right away, then use something to soak up the spill instead, such as paper towels or cat litter. Once you have most of the liquid cleaned up, scrub the area with the vinegar or baking soda and then mop it one last time with water.
For a cool video on acids and bases, click
You'll notice that both the acid and the base react with the metal. Listen closely at the beginning to find out about why.
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