Introduction to Acids and Bases
Every liquid is either acidic or basic except for water.
Acid comes from the Latin term
acere, which means "sour". Acids such as lemon juice and vineger, taste sour, are corrosive to metals, and change litmus (a dye extracted from lichens) red. Another definition for acids is a solution that has an excess of H+ ions.
Bases taste bitter, feel slippery and change litmus blue. Another definition of a base is a solution that has an excess of OH- ions.
Scientists use something called the
pH scale to measure how acidic or basic a liquid is. A very strong acid will have a pH of 0. A very strong basic solution will have a pH of 14. Water has a pH of 7 because it is neutral.
The table below shows examples of some acids and bases.
| [H+] | pH | Example |
| Acids | 1 X 100 | 0 | HCl |
| 1 x 10-1 | 1 | Stomach acid |
| 1 x 10-2 | 2 | Lemon juice |
| 1 x 10-3 | 3 | Vinegar |
| 1 x 10-4 | 4 | Soda |
| 1 x 10-5 | 5 | Rainwater |
| 1 x 10-6 | 6 | Milk |
| Neutral | 1 x 10-7 | 7 | Pure water |
| Bases | 1 x 10-8 | 8 | Egg whites |
| 1 x 10-9 | 9 | Baking soda |
| 1 x 10-10 | 10 | Tums® antacid |
| 1 x 10-11 | 11 | Ammonia |
| 1 x 10-12 | 12 | Mineral lime - Ca(OH)2 |
| 1 x 10-13 | 13 | Drano® |
| 1 x 10-14 | 14 | NaOH |
Taken from
http://www.visionlearning.com/library/module_viewer.php?mid=58
Cabbage Juice pH Indicator
Introduction
Red cabbage has a pigment called anthocyanins. The pigments give it the red/purple color. Very acidic solutions will turn anthocyanins red and basic solutions will turn anthrocyanins green/yellow.
Hypothesis
We can determine the pH of a solution by adding it to cabbage juice. An acidic solution will turn the cabbage juice red and a basic solution will turn the cabbage juice yellow.
Materials
- red cabbage
 |
| Red Cabbage-chopped |
- 12 glass containers
- ammonia
- lemon juice
- vinegar
- antacids
- seltzer water
- HCL (hydrocholoric acid)
- NaOH (sodium hydroxide)
Procedures
1. Chop the cabbage into small pieces and boil in water for a couple of minutes until the liquid turns a dark purplish color.
2. Pour a little bit of cabbage juice into 6 empty glass containers.
3. Prepare the 'test' acid/base solutions into 6 glass containers.
4. Pour a few drops of the test solution into the cabbage juice containers and write down what happens.
 |
| Cabbage juice in glass vials |
Results
NaOH- turned the cabbage solution yellow
 |
| Antacids added to cabbage juice |
Ammonia- turned the cabbage solution yellow
Antacids- turned the cabbage solution bluish-green
Seltzer water- nothing happened.
Vinegar- turned the cabbage juice red
Lemon juice- turned the cabbage juice red
HCL- tunred the cabbage juice red
 |
| Seltzer water added to cabbage juice |
 |
| Vinegar and Lemon juice added to cabbage juice |
 |
| NaOH and Ammonia added to cabbage juice |
 |
| HCl added to cabbage juice |
Conclusion
We found that NaOH, ammonia, and antacids are bases. Vinegar, lemon juice and HCL are acids. The seltzer water is neutral.
At the end we mixed a base (NaOH) and an acid (vinegar) together. When we poured a little bit of the basic solution into the acid, we got a violet color. When we poured a little bit more of the basic solution, the violet solution turned green.
 |
| Adding NaOH to Vinegar |
 |
| The result of NaOH added to Vinegar |
 |
| Adding more NaOH to vinegar |
 |
| The result of adding a lot of NaOH to Vinegar |
Can you explain these results?
