tions acidic to basic, versa. In titration where an acid and a base are change from and vice indicator present to signal when enough of the one has together it is to have an appendix, table A.5, for a listing been added to neutralize the other. Refer to the of common indicators, their color ranges, and their transition points. A drops in a Generally, indicators are availab in laboratories as aqueous solutions. few sample usually is sufficient to show a definite color. Sometimes indicators are impregnated in strips of that can be dipped into a solution. Litmus papers, which turn blue in base and red in paper in use are universal indicator papers, called p acid, a common examples. Increasing usually from very red papers. They show a continuous change of color over a wide pH range, by color hue the for pH 1 pH pH papers, which can indicate pH of a solution to within a few tenths o a are also available Laboratories requiring rapid accurate measurements usually use a pH meter The theory behind it is easy to use: you place an appropriate pair of elec- sample and read the pH dial. The measurement based upon the experimental fact that a change in hydrogen ion concentr can change of an electrochemical cell The pH meter is fast and consequently is especially valuable when testing many samples. It is also preferred for dark or colored solutions where indicator colors may be obscured. In today's experiment you will see how indicato work. You will explore their color ranges and locate the pH of their color transitions. You will do this by making some reference solu- tions of known pH and observing the colors of various indicators in each of them. You will then use your knowledge to determine the p of several common materials. Finally, if time use the pH meter to check some pH values. permits, you may have an opportunity t