You can buy litmus paper or a pH meter to measure the pH of a substance. An easy alternative indicator, however, is red cabbage juice. Its natural color is blue-violet, but when in contact with an acid it turns red/pink. Add it to a base and it turns blue/green or yellow. Make cabbage juice by boiling chopped red cabbage in a pan for half an hour and draining out the juice. Use it to test the acidic and basic properties of common colorless or white liquids such as distilled water, tap water, vinegar, lemon juice, milk and baking soda solution.
Acids react chemically with bases to form salt and water. This is called a neutralization reaction because the liquid that is produced -- water -- is neither acidic nor basic. Sometimes these chemical reactions are accompanied by the emission of a gas and can be quite explosive. The popular volcano experiment is just this kind of reaction. The outside of the volcano is made of scrunched up scraps of wet newspaper mixed with glue. The lava is produced by adding vinegar, an acid, to baking soda, a base, plus a drop or two of red food coloring. The reaction produces carbon dioxide, water and sodium acetate in a satisfying red froth.
A high concentration of sulfur dioxide and nitrogen oxides in the atmosphere results in precipitation that is acidic. This can be damaging to plants, water bodies, soil and buildings. You can study the effect of acid rain on plants by growing cuttings of philodendron and begonia in distilled water and water mixed with vinegar. After a few weeks you will notice that the plants placed in distilled water grow much faster than the ones in the vinegar-water cups.
Metals that come in contact with acids react chemically and are dissolved slowly. To observe this effect, place a few copper pennies in a cup of water and a few more pennies in a cup of vinegar or lemon juice. Use pennies minted before 1983, because the composition of pennies was changed after that time. After a few days you will notice that the water cup looks just the same but the cup with the vinegar or lemon juice contains bluish-green liquid. This is due to the chemical reaction between the vinegar or lemon juice and the copper in the penny.