You have probably heard the terms acid and base before, but what do they mean? To help explain, we'll first talk about water and the elements that combine to form it. Then we'll talk about the role of pH in acids and bases.
Most acids and bases that we encounter in common use are usually liquid solutions. These solutions are formed from molecules that dissolve in water to give ions. Ions are atoms with an excess or deficiency of electrons, which gives them positive or negative charges. Water is formed from a balance of hydrogen and oxygen ions. Hydrogen has one positive charge, while oxygen has two negative charges. Therefore, two hydrogen ions are needed to balance the oxygen ion so water's overall charge is zero. This is because all matter is fundamentally neutral in charge or strives to become neutral.
Some chemists define acids as substances that can add hydrogen ions to a solution, while bases are substances that can take away hydrogen ions from solution. So, substances that have an excess of hydrogen ions are acidic. Alternatively, substances that are lacking hydrogen ions are basic. Every solution is generally either acidic or basic. Even tap water can be either slightly acidic or basic due to the natural elements like calcium or magnesium that are often naturally found in it.
The pH scale is used to indicate how acidic or basic a solution is compared to a neutral substance like water. The pH scale ranges from 0-14: pure water is has a pH value of 7 (the value for neutral substances), acids have pH values less than 7 (down to 0), and bases have pH values greater than 7 (up to 14). The acidic strength of a solution is higher as the pH value is lesser. Likewise, basic strength of a solution is higher as the pH value gets closer to 14.
But, how do you determine a pH value? A pH indicator is often used to estimate the pH value of a solution. The indicator is typically a chemical that changes color if it comes in contact with an acid or a base. There are many different kinds of chemical pH indicators, but a natural indicator is red cabbage juice. Red cabbage juice changes color when an acid or base is added to it. The juice generally turns dark red when an acid is added, while it usually turns green or yellow when a base is added.
Little Lion Experiment:
Most homes have a variety of items that are acidic or basic. This experiment will allow you to determine if common solutions around your home are acidic or basic using red cabbage juice. You will want to have the help of a parent or guardian throughout this experiment, especially when making the cabbage juice and when testing the items gathered from around your home.
Items Needed:
- Stovetop
- Head of red cabbage
- Water
- Pot for boiling water
- Ladle
- Disposable cups/bowls (plastic may get stained red)
Steps:
- Rip or cut the red cabbage into pieces (they should be small enough to fit in the pot).
- Add some water to a pot, and begin to boil the water on the stovetop (the amount of water should be similar to the amount used to cook pasta).
- Add the shredded cabbage to the boiling water and let it cook for approximately 10 minutes.
- After both the water and pot cool down, use the ladle to spoon the liquid only into the bowls. The red cabbage juice is usually violet in color. Now you are ready to test some solutions from around your home to determine if they are acids or bases!
Some items you can test in your cabbage juice include (but are not limited to): orange juice, lemon juice, windex (with ammonia), vinegar, baking soda, soda pop, laundry detergent and antacids (like TUMS or Maalox). You can test any solution in the juice, but the items listed above should give good results! To test a solution, you just add some of the solution to the juice and see what color it changes to.
Questions:
- Which of these items were acids or bases?
- What different colors did the juice turn in the presence of the acids or bases?
- What colors would the juice change to if you first added a solution that was acidic to the juice, and then added a basic solution?
- What color would the juice change to if you first added a base to it and then an acid?
