A great deal of the substances that you encounter everyday are either acids and bases. This site is meant to give a very general introduction to what acids and bases are and how we chemists characterize substances as acids and bases. On this page, we will discuss various definitions for acids and bases, the pH scale, indicators, and even how to make your own acid base indicator. Also, check out the embedded links to learn more about certain topics.
There are so many different ways to define what an acid or a base is chemically. The simplist explaination is the Arrhenious definion. This simply states that acids increase the hydrogen ion concentration (H+) of solutions and bases increase the hydroxide ion concentration (OH-) of solutions. The Bronstead-lowry definition is related to the Arrhenious definion, but it is a bit more detailed. It defines acids as proton donors and bases as proton acceptors. Now I did say that this is related to the Arrhenious definition and it is. If you thing about a hydrogen atom, you see it only has one electron and one proton. So if you take that electron away to make it a cation, you re left with a proton. So when I say acids are "proton donors", I am saing that acids are "Hydrogen ion donors". So that is how acids, in a way increase the hydrogen ion concentration. Bases are a little more difficult to explain. When a base interacts with water, it accepts a hydrogen ion from the water molecule. What's left is a hydroxide ion. So that is how bases increase the hydroxide ion concentration. By the way, water can act as an acid or a base. When it interacts with a base, it acts as an acid (it donates protons). However when it interacts with an acid, it acts as a base, meaning it accepts the acid's proton.
Are you very confused right now? You probably are!! Its ok to be confused. Check out Chem4kids for other explanations of acids and bases. . If you are still unsure, ask your chemistry teacher or professor. When you grasp this definition, move on to something a bit harder, Lewis Acids and Bases. This article also has more information about acid and base reactions.
Some acids and bases can be told apart by taste or touch. Orange Juice and lemons contain citric acid. You can tell that they have an acid in them because they taste kind of sour or tart. Milk and Tums are bases. They taste a little bitter and feel slippery. However, you definitely cannot taste and touch all acids and bases, some are highly dangerous and can cause serious injury. For example, sulfuric acid can be strong enough to dissolve bones and eat through metal. Sodium hydroxide (lye) can cause very seriuos burns. So how can we tell if these things are acids or bases? One way is to use an indicator.
An indicator is a chemical that interacts with an acid or a base to produce a color change. This color change can tell you if a chemical substance is an acid or a base. In some science classes , you have probably used litmus paper. Itmus paper has a chemical in it that turns red when it comes in contact with an acid and blue if it comes in contact with a base. Other examples include methyl red, phenolphthalien, and btrothymol blue.
Wnana test stuff in your own home to see if they are acids and bases. You can find out how to make an acid base indicator from red cabbage jucie by clicking here.
The pH scale is another way that chemists can tell if a substance is an acid or base. The pH scale is based on the hydrogen ion concentration in a substance. Of course, an acid would have a higher hydrogen ion concentration than a base . We get this skale by taking the negative logarithm of the hydrogen ion concentration. This gives us easy numbers to use ito classify things as acids or bases. The pH scale goes from 0 to 14. If a substance is an acid, it has a pH that ranges from 0-6. If a substance is a base, it has a pH of 8-14.A pH of 7 tells you that the substance is neither an acid or a base, or it is neutral. Chemists measure the pH of substances by using a pH meter which is a machine that is attached to an electrode. The machine or meter gives the pH number.
pH is very important in biology exspecially. Your stomach keeps a pH of around 2 to help digest food. If you get any lower, you could be dealing with heart burn. Also the blood that runs through your veins keeps a pH of around 7.
If you want to take a look at a pH scale graphic, click here.