How do you tell acids from bases?
When an acid dissolves in water, it releases hydrogen ions, H+. A base releases hydroxide ions, OH−. Pure water contains equal amounts of the two ions, so it is neutral. Acidic and basic properties differ in these ways:
| Property | Acid | Base (alkali) |
|---|---|---|
| pH | below 7 | above 7 |
| Litmus | turns red | turns blue |
| Reactive metals | react and release H2 | most do not react |
| Carbonates | react and release CO2 | no CO2 is released |
| Taste and feel | sour | bitter, slippery |
Taste and feel are textbook properties only. In the lab, never taste a substance or test it with your hands.
The pH of seven substances
The values come from the simulator. The pH of a real product can differ depending on what it contains.
| Substance | pH | Category | Scale color |
|---|---|---|---|
| Lemon | 2 | acid | red |
| Vinegar | 3 | acid | orange |
| Coffee | 5 | acid | yellow |
| Water | 7 | neutral | green |
| Washing soda | 9 | base | blue |
| Soap | 10 | base | blue |
| Caustic soda | 13 | base | purple |
Each time the pH drops by one unit, the H+ ion concentration increases 10 times.
How is a base different from an alkali?
A base that dissolves in water is called an alkali. One example is caustic soda, NaOH. That is why the simulator classifies a substance as a base and labels its solution alkaline, which means the same as basic. Washing soda and soap are salts, but their solutions are alkaline.
Compare substances on the pH scale in the Nalukh chem app
This simulator is part of full access. The app is free to download, and 2 chapters and 5 simulators are open without sign-up.
How do you use the simulator?
- Choose a substance from the bottom row: Lemon, Vinegar, Coffee, Water, Washing soda, Soap, or Caustic soda.
- The top line shows the substance's name, its category, and its pH value. The category is one of three: Acids, Neutral, or Bases.
- A black arrow moves to that pH on the scale. The numbers 0, 7, and 14 on the scale mark the two ends and the middle.
- Look at the colors on the scale: red, orange, and yellow are acidic, green is neutral, and blue and purple are basic.
Tasks to try in the simulator
- Find the most acidic substance and the most basic substance. Answer: Lemon (pH 2) and caustic soda (pH 13).
- Find two substances that are the same distance from pH 7. Answer: Coffee (pH 5) and washing soda (pH 9).
- How many times more acidic is vinegar than coffee? Answer: The pH difference is 2, so 100 times.
Common mistakes
- pH 0 does not mean there is no acid. It means a very strongly acidic solution.
- Thinking that basic substances are safe. A solution at pH 13 burns just as an acid does.
