An acid is a hydrogen ion donor. There are strong and weak acids.

Let's revisit the ChemTeam site, this time focusing on the historical understanding of what an acid is. Please go to the site http://dbhs.wvusd.k12.ca.us/AcidBase/AcidBase.html and write a short essay comparing the definitions of an acid as discussed by Laviosier, Davy, Liebig and Arrhenius. Which definition(s) is or are the best? Why?

Acids are strong or weak, depending upon their nature, but their solutions can be concentrated or dilute, irrespective of their nature. We use molarity to quantitatively describe their concentration.

J.T. Baker Chemicals is one of several large chemical manufacturers and distributors. Typical of the chemical industry, they sell concentrated acids listing their "w/w" ("weight-to-weight") ratios. This means the mass of, for example, hydrochloric acid to mass of solution, is about 33-36% w/w, meaning 33 to 36 g HCl to 100 g solution. In order to calculate the molarity of HCl in this concentrated solution, you also need to know the density. Manufacturers use the specific gravity, which is a measure of the density relative to water at 4oC, which for HCl is 1.18 kg/L, or 1.18 g/L.

Please go to the J.T. Baker catalogue site at http://www.jtbaker.com/asp/Catalog.asp and, using the search function (with full names rather than formulas) look up several strong acids. Using data provided on the page (specific gravity is on the bottom), please calculate the molarity of four common acids.

A base is a substance that accepts hydrogen ions.

The chemical industry uses names that we generally don't use in the more formal chemistry classroom. But the substances are so very important that we ought to know about them. One such substance is caustic soda, sometimes called, simply, caustic. Search the Web to find out the following information. What is it? What is it used for? And why do we have you investigate it in this section of the text?

Group 1a and 2a metal oxides are all strong bases. Oxides of non-metals generally form acidic solutions in water.

Organic anhydrides are very important industrially. One example is acetic anhydride. There are many others. Find out about the properties and uses of acetic anhydride by surfing the Internet. Are there other organic anhydrides that have the same sales of billions of kilograms per year? What are they used for?

The pH scale is a convenient way to measure acid concentration in aqueous (or any other solvent) solution. Each unit change in pH represents a change in acid concentration of a factor of 10.

The federal Food and Drug Administration (FDA) released a report in 1997 discussing alpha hydroxy acids (AHA's) in cosmetics. The discussion can be found at the site http://www.fda.gov/opacom/backgrounders/alphabg.html. Why is the FDA concerned about AHA's? How does this relate to our discussion on pH? What is the FDA's recommendation regarding AHA's in skin care products? Why? You may want to read the paper at the site http://www.shikai.com/info/alpha.htm, which gives further information.

pH values of aqueous solutions generally fall in the 0 to 14 range. It is possible to calculate the hydrogen ion concentration given the hydroxide concentration, and vice-versa.

Let's revisit the FDA. They have a list of the pH ranges of common (and not so common) foods at the site http://vm.cfsan.fda.gov/~comm/lacf-phs.html. What can you say about the pH range of foods? Is there a general rule about food pH? Which foods are exceptions to the rule? Can you generalize about the foods that are, themselves, exceptions?

There are many indicators of acid concentration, including plants, as well as commercially-prepared products.

We discuss anthocyanins in this section's case-in-point. But nature has another, related indicator in plants called betacyanins, part of a larger group of betalains. Look on the Internet to answer the following. What are betalains and betacyanins? How are they different from anthocynains, and how can you tell these groups apart?

Neutralization occurs when sufficient base is added to an acid to stop its proton-donating capability. Adding sufficient acid to base will stop its hydroxide-donating capability (the base will be neutralized.)

Here's a cute simulator that gives the products of several acid/base neutralization. http://www.openteach.com/chemistry/acidbase.html. Try dragging an acid and base to the reaction flask and write down the products. Try several different combinations. Remember to empty the flask into the waste bucket after each reaction!