Purple cabbage

All I could eat after that was a little bit of broccoli, carrots and purple cabbage, and that came right through me unchanged. I was really scared. 

Pour a half cup (120 milliliters) of vinegar and a half cup (120 milliliters) of water into the bottle and swirl to mix. A two-liter soda bottle may be substituted if you use twice as much vinegar and water. Add enough purple-cabbage indicator so that the resulting solution is bright pink, but do not add more than one tablespoon. 

Gas production is a good indication that a chemical reaction has taken place. Color change is also an indication of a chemical reaction however, in this case the reaction could have proceeded just as well without the purple-cabbage indicator and without changing color. The purple-cab-... 

To see how this works, put on your safety glasses and then add about a tablespoon (15 milliliters) of purple-cabbage indicator (prepared as outlined in the Shopping List and Solutions ) to a cup (240 milliliters) of water and observe the color. It should be light lavender. Now make up a saturated solution of baking soda in water. A saturated solution is one in which no more solid can be made to dissolve. Baking soda is not very sol-... 

Using one-cup (240-milliliter) samples of saturated baking soda solution, vinegar, ammonia, and water, you can set up the following banks of solutions and observe the colors that result when you add purple-cabbage, swimming-pool, or fish-tank indicator. 

Now take some of the clear, carbonated soda that was a suggested purchase in the Shopping List and Solutions and add the purple-cabbage indicator. You should observe a pale pink solution. Carbonated soda... 

So what are acids and bases Vinegar is actually a dilute solution of acetic acid in water, about a 5 percent solution, but it rather nicely displays the characteristic properties of acids they are sour, they turn purple-cabbage indicator red or pink, and they react with bases to form water. A solution of sodium bicarbonate nicely displays several of the characteristics of basic solutions it tastes bitter, it turns purple-cabbage indicator blue, and it reacts with acids to form water. The last property, listed for both acid and base, the ability to react with each other, is really the defining property because acid-base reactions, like redox reactions, occur in tandem one substance acts as an acid and one substance acts as a base. Acid neutralizes base and base neutralizes acid. 

In this demonstration, we first isolate the active ingredient of the modem form of aspirin, acetylsalicylic acid, using a time-honored organic chemistry procedure called extraction. The preparation of purple-cabbage indicator is a type of organic extraction the organic purple dye is extracted from the cabbage with water. Here we use alcohol to extract acetylsalicylic acid from aspirin. 

Universal indicators are mixtures of several acid-base indicators that display a continuous range of colors over a wide range of pH values. Figure 18-2 shows concentrated solutions of a universal indicator in flat dishes so that the colors are very intense. The juice of red (purple) cabbage is a universal indicator. Figure 19-2 shows the color of red cabbage juice in solutions within the pH range 1 to 13. 

Figure 19-2 The juice of the red (purple) cabbage is a naturally occurring universal indicator. From left to right are solutions of pH 1, 4, 7, 10, and 13.

If boiling water be poured on a few slices of purple cabbage, thereby making a solution of the same, then an alum solution turns this green a potash, purple and hydrochloric acid, crimson. 

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