As I got older, I was delighted to find that you didn't need a chemistry set to have fun with chemistry. Everything is composed of chemicals! Check out these colorful reactions.
The big depression in the spot plate is filled with the juice from some beets my son cooked the night before, butter and all! The upper depression has a solution of baking soda. The one below it has tap water. The bottom depression has some rice vinegar in it. The color is from beet juice.
The reason the colors are different is pH. So, what is pH?
p functions (there are many that are used in chemistry) are ways of reporting concentration, especially concentrations of ions in solutions. pH, specifically, tells the concentration of hydrogen ions (that's what the H stands for) in a solution. Acids are substances that place hydrogen ions into a solution; bases are substances that take them out, usually putting hydroxide ions in instead. Concentrated acids and bases are very reactive.
I used to sell car batteries. The sulfuric acid in car batteries will dissolve cotton and turn your skin into parchment. I couldn't keep blue jeans and my knuckles would crack to the bone. A strong base like lye will also take your skin off. Of course, sometimes you want a concentrated acid or base. Strong lye solutions are used in the manufacturing of soap.
The hydrogen ion concentration can range from 0.1 mole per liter in a very concentrated acid to 0.00000000000001 moles per liter in a very basic solution. These numbers are disturbing, but the negative logarithms (base 10) are 1 and 14. That's what a pH is, a negative logarithm, and that's why they're used.
The logarithm (base 10) of 10 is 1, 100 is 2, 1000 is 3, and so on. See? The number of zeros tells you the logarithm. Between each multiple of 10, the logarithms will be between whole numbers. For fractions, the logarithm of 1/10 is -1, 1/100 is -2, 1/1000 is -3, and so on. p function values are negative logarithms so that small numbers will be positive values.
Pure water at room temperature and atmospheric pressure at sea level has a pH of 7 and that is considered neutral because there are the same number of hydrogen ions as there are hydroxide ions. That makes sense because each water molecule splits into a hydrogen ion (actually, each hydrogen ion binds with a water molecule to form a hydronium ion) and a hydrogen ion.
It's nice to have a way to test for acids and bases. Enter beet juice...
Many plants (not just beets) have compounds called anthocyanins. In fact, many of the reds and purples of autumn are from anthocyanins in leaves of trees that are masked during the spring and summer by chlorophyll. Blue and red flowers are often colored by anthocyanins.
But why do they change colors with acids and bases?
Anthocyanins are acids that can lose hydrogen atoms to form basic ions. The neutral molecule and the ion have different colors. In the case of beet juice, it's red when there's a lot of hydrogen ions (in an acid) and yellow when most of the hydrogen is tied up (in a base). Beet juice turns from red to blue to yellow as it becomes less acid and more basic. The yellow color only shows in extremely basic solutions...pH 11 and higher. The sodium bicarbonate solution in the photograph is only weakly basic.
I used to take different colored flowers and hang them above ammonia cleaning fluid, a base, or hydrochloric acid, an acid. The vapors the fluids give off are also basic and acidic. You should try it. The color changes are dramatic.
I would also make violet syrup. If you can find a big patch of violets (don't destroy a whole patch of flowers just to make syrup), pack a Mason jar full and pour hot simple syrup over them (half water and half sugar by volume). Stretch some plastic wrap quickly over the mouth of the jar until it cools (you don't want to lose any of the violet flavor), and then screw the lid on for a day. You'll end up with a dirty blue liquid. That's the basic color. Now add just enough lemon juice to turn the fluid a beautiful magenta. That's the acidic color. You have a tasty, violet flavored syrup. I think it tastes like wildflower honey.
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