Science with Sydney
pH Indicator
What does pH stand for and what does it mean?
The “p” stands for potential and the “H” is the chemical symbol for hydrogen. That will make a little more sense in a bit. So, what does pH mean? pH is a measure of how acidic or basic something is. You have probably heard of acids before. You have acid in your stomach, acid is in batteries, and acids have all kinds of industrial uses. When you think of acids, you probably picture a liquid that can burn through skin, metal, or stone… well, some acids can do this, especially very strong acids. They are very dangerous. On the other end of the scale are bases. We don’t really hear much about bases but they can be very much like acids in the fact that they are also very corrosive and damaging when they are very strong. A strong acid and a strong base can do equal damage.
The “H” in pH
Like I said earlier the H is for hydrogen, more specifically, hydrogen ions. Hydrogen ions are written as H+. Acids have an abundance of these hydrogen ions (H+) and therefor can donate them to bases. That’s why we say that acids donate hydrogen ions. Bases on the other hand are just the opposite. They lack hydrogen ions (H+) and therefor accept them from acids. Bases accept hydrogen ions.
What about the scale?
pH is measured on the pH scale. This scale runs from 0 to 14. At the 0 end are acids and on the 14 end are bases. Now I know what you are thinking, “if acids have more H+ then why do they have a low pH, and if bases have lower H+, why do they have a high pH?” If you remember, the “p” stood for potential. What is their potential for H+, or how likely are they to gain more H+. Remember acids donate H+ and therefore have a low potential (a low pH). Bases accept H+ and therefore have a high potential (a high pH). This can be confusing at first but if you remember what the p and the H stand for and what acids and bases do, it will start to make a lot more sense. In the very middle of the scale is 7 (half of 14 is 7). Here at 7 is considered neutral, it is neither acidic nor basic. If all of this wasn’t confusing enough, there is one more very important thing to know about the pH scale. The scale is not a regular scale, it is something called a logarithmic scale. This means that each step on the scale represents a ten time difference, not a one time difference. For example, a base with a pH of 12 would be 10 times more basic than a base with a pH of 11. Also, an acid with a pH of 2 would be 100 times more acidic than an acid with a pH of 4. Look at the scale and start at pH 7, each step up the scale is 10 times more basic, each step down the scale is 10 times more acidic.
Watch Sydney
Now it’s your turn to do this experiment. The only thing you really need is a red cabbage, the rest of the stuff you can find around the house. If you want you can download the following document and use it during your experiment, then test yourself with the knowledge check. Have an adult help you if you need. Most of all have fun!
Click to download pH Indicator worksheet
