Summer Science: Acids and Bases
June 2, 2015

This summer when it’s hot and you jump into a nice, clear swimming pool, think acids and bases! Someone has tested the water and adjusted the pH level. Or, when you relax drinking your favorite carbonated beverage, think once again about acids and bases (carbonic acid- H2CO3). How about a toasted cheese sandwich? Rennet (a complex of enzymes isolated from stomach acid) is added to milk, which acidifies and curdles the proteins in the milk. The curds are collected to make cheese. Or, if you overdo it and your muscles are sore, blame it on lactic acid.

Acids and bases are chemical compounds that have distinctive properties in water solution. The sour taste of a lemon, lime, or grapefruit, for example, is caused by citric acid. The slippery feel of ammonia, a common base, is characteristic of all bases. One of the most interesting properties of acids and bases is the way they react with indicators. An indicator is a material that changes color in the presence of an acid or a base. For instance, the beautiful hydrangea flower can be either pink or blue, depending on the amount of acid or base present in the soil in which it is planted.

The most precise pH measurements are made with electronic pH meters. However, simpler materials are also used. Best known among these is litmus paper (made from an extract of two lichen species), which turns blue in the presence of bases and red in the presence of acids. The term "litmus test" has become part of everyday language, referring to a make-or-break issue.

Yes, acids and bases (alkali) play a role in our lives on a daily basis. This month we offer two more acid/base science activities that use indicators (litmus paper and goldenrod paper).

Here’s some interesting acid/base trivia centered on a common medicine we’re all familiar with: Alka Seltzer®. Citric acid plays a role. This in itself is interesting, since antacids are more generally associated with alkaline substances, used for their ability to neutralize stomach acid. The fizz in Alka-Seltzer®, however, comes from the reaction of citric acids (which also provide a more pleasant taste) with sodium bicarbonate or baking soda, a base. This reaction produces carbon dioxide gas. So when you drink this mixture to sooth your upset stomach (maybe like in the Quirkles Andy Acid book), you’re getting a concoction made up of both an acid and a base!

Enjoy your summer and look for ways to teach science in your everyday activities!