Acids and Bases in Everyday LifeLothar Graudins, Ph.D

COPYRIGHT 2009

We have all heard about the assumed hazards of acids, some of which reportedly “go right through your skin and eat your flesh.” While certain acids need to be handled with care, this view is largely tainted by Hollywood sensationalism and social hysteria. In fact, most acids and bases are not particularly dangerous. Even injury from contact with the concentrated laboratory versions is minimized to a minor irritation if you quickly rinse the contact area with cold water. Of course, such injury is easily avoided by proper storage and handling. To avoid injury to others, all chemicals should be locked up. One should always wear rubber gloves and goggles whenever you work with common laboratory acids, namely the mineral acids: Sulfuric, Hydrochloric and Nitric. Sulfuric Acid, incidentally, has historically been the most important and widely manufactured chemical. Its annual world-wide production is still measured in the millions of tons. It is used in numerous industries, such as the manufacture of superphosphate fertilizer and a host of important agricultural chemicals. Iron and steel industries use Sulfuric acid to remove oxide coatings. The petroleum industry is a heavy user. This acid is commonly used in automobile batteries, in the manufacture of explosives, photographic film, synthetic fibers, medicines, paints and pigments. The mining industry uses dilute Sulfuric acid to separate ores from raw minerals. Concentrated Sulfuric acid is a powerful drying agent and is thus used to withdraw water from various reactions. You may have seen the dramatic reaction, whereby Sulfuric acid is poured over sugar. The acid removes the water from the molecule, leaving a black and crusty residue of carbon. Considerable heat is released in this reaction, as is the case whenever the concentrated acid is diluted with water. It is for this reason that water is never added to concentrated sulfuric acid. Instead, when making a dilution, you must slowly add the acid to the larger amount of cold water.

Organic acids and bases are widely used in our body to regulate a variety of functions. They tend to be very weak in comparison to mineral acids. There are a variety of (chiefly) organic acids and weak bases commonly found in the home. Such substances are found in our foods, medicines and cleaning products. Consider the following:

1.) Acids are sour-tasting. Lemon juice and vinegar are common acids. I have mentioned battery acid, because it is commonly used in our automobiles.

2.) Bases, or alkaline substances, taste bitter. Baking soda, “Tums”(an anti-acid tablet, ) Milk of Magnesia, Lime water and household lye (example: “Drano”) are

examples of bases.

The measurement of relative strength of either acids or bases is done with a pH scale.By strength, in general, we mean the degree to which ions are formed. In this case, we mean hydrogen ions. Technically, the hydrogen ion concentration is measured on a scale of 1 to 14, with a neutral point at 7. Water is considered to have a pH of 7, where we find hydrogen ions and hydroxide ions in balance. If you move up the scale, the substance is increasingly alkaline. Moving down the scale means a higher number of hydrogen ions, or an acid environment. Each step on the scale is based on a factor of 10. For example, a pH of 6 means 10 times the acidity from neutral 7. A pH of 5 means 100 times the acidity from neutral. Conversely, a pH of 9, means a 100 times the alkalinity from neutral. The chart A in the index illustrates this relationship. Note that positive exponents are used in designating pH. For example, lemon juice has a pH of 2, whereas baking soda, on the alkaline side, has a pH of 8.

In summary:

1.) An acid is a solution that has an excess of hydrogen (H+) ions. A base is a solution with an excess of hydroxyl (OH-) ions.

2.) A strong acid is an acid that has a very low pH (0-4). A strong base has a very high pH (10-14).

3.) Weak acids and bases only partially ionize in a water solution.

Certain complex organic substances such as vegetable dyes may serve as indicators or coloring agents that form colors at certain pH levels. One such indicator is found in red cabbage juice. You can easily extract this indicator. Concentrated red cabbage juice is obtained by shredding red cabbage and either extracting the juice with a blender and cold water, or, by boiling the cabbage for 15 minutes. Pour the extract through a coffee filter and refrigerate. Cabbage juice is deep purple in color in a neutral environment (pH 7). In the presence of an acid, it turns deep red. With alkaline substances, it changes color to a striking deep green. Corresponding colors are obtained for subtle pH changes.

Figure 1 below shows the brilliant colors of four pH values.

Figure 1. Brilliant colors are produced with Cabbage juice indicator. Starting with the bottom tube, the approximate pH values are 2, 5, 7 and 14.

Experiment: Determining the approximate pH value of common substances.

In this experiment you will test different substances with cabbage juice indicator and note resulting colors. Next, a number of standards are developed that indicate approximate pH values.

What you will need:

1.) 100ml of concentrated indicator solution made from fresh red cabbage. (See above for preparation.)

2) 5 ml of battery acid (dilute Sulfuric) or dilute Hydrochloric acid.*

3)10ml of fresh lemon juice, filtered through a coffee filter.4.) 5ml of household vinegar (dilute Acetic acid)5.) 5ml milk6.)Baking soda (Sodium Bicarbonate) solution. Mix 1 tsp. of baking soda with 20ml of water.7.) 5ml household Ammonia (dilute Ammonium Hydroxide)8.)5ml of dilute lye (Sodium Hydroxide)solution. Dissolve ½ tsp. Lye in 5ml water.

9.)10 small test tubes and rack10.) Several eye droppers

*If this experiment is used for a science fair project or in a public setting, avoid using reagents (2) and (8).

Procedure:

Line up each of the test tubes and add 10ml of cabbage juice indicator solution to each tube. Number the tubes and add 5 drops of each solution, from #2 through #8.Be sure you rinse the dropper(s) thoroughly after each addition. Shake well. Use a white sheet of paper behind the tubes to better see the colors. List the approximate pH value for each tube. (Refer to Appendix, pH scale )

Have a friend or companion prepare several solutions just as you did, but in your absence. Can you match these “unknowns” to your samples? Standards are made by using known concentrations associated with a specific color. These standards are then compared with a sample of an unknown concentration. The use of standards, known concentrations or known characteristics of some physical phenomenon is common throughout the science of chemistry. We can compare something we have measured or quantified with something we wish to measure. A balance is a simple example. When we wish to know the mass(weight) of an object, we compare it to some known weight until balance is achieved.

A practical application:

If you have access to a pool or a jacuzzi, the above experiment will help you to understand pH values as well as the use of indicators. In fact, the basic need for a pool is to balance or stabilize the pH level. In turn, this allows the chlorine (or bromine) to function effectively. It is important to initially know about the characteristic of the water in your area of the country. In Nevada, for example, untreated water often has high levels of calcium carbonate, an alkaline material that reads well above 7 on the pH scale.For effective chlorination, we would like the pH to read between 7.2 to 7.8. The chlorine

level is ideally between 1.5 to 3.00 parts per million (ppm), although this range could be extended from 3-5 ppm in a spa.

Don't be afraid of using a test kit. (See Figure 2.) A kit such as this uses phenol red as an indicator of the pH value. Chlorine or Bromine levels are read in ppm. Notice the use of color standards that are easily read and allow you to compare colors with known pH values. The test takes only a few minutes and given you reasonably accurate data. At this point, depending upon the readings, you can use an included chart to tell you how much of a chemical to add. This of course will depend upon the size of your pool or spa. Once you stabilize the water, it takes little effort to maintain. You will develop an intuitive sense (based upon careful observation) on how much of chlorine or acid (to lower pH) to add.

Figure 2. An inexpensive and easy to use test kit will provide the pH and chlorine levels of your pool or spa water.

I recommend using Muriatic (Hydrochloric Acid) to lower the pH. This is usually available from a pool store. Powdered material (sometimes called pH Down) tends to precipitate insoluble salts. This makes the water very cloudy. If you need to raise the pH, an alkaline additive such as soluble Sodium Carbonate is available. A commercial product, pH Increaser, has 97% available Sodium Carbonate.

In summary:

1.) Call a local pool business or your municipal water company to find out about the kind of water in your area.

2.) Buy and use a simple test kit. You can do this!3.) Keep your pool clean of debris.4.) Stabilize and enjoy the water.