Resumen de Demonstration Extensions Based on Color-Changing Goldenrod Paper
Donald K. Schorr, Dean J. Campbell
For many years, a type of goldenrod-colored paper has been used as an indicator to demonstrate acid–base behavior, turning yellowish in acidic conditions and reddish in basic conditions. This pH sensitive color change has been the basis of demonstrations involving making hidden messages and pictures using techniques such as printing (e.g., to make a “bloody” red handprint), spraying, wax resist, and electrolytic processes. Candidate dye compounds for the goldenrod paper that feature a pH sensitive yellow/red color change include Direct Yellow 4 and curcumin. Direct Yellow 4, curcumin, and the color-changing goldenrod paper also all exhibit additional changes to darker colors in very acidic solutions (pH < 0). This paper provides evidence that Direct Yellow 4 (or a closely related compound) and not curcumin is the dye present in the color-changing goldenrod paper. These color changes of the Direct Yellow 4 in the goldenrod paper, in conjunction with the fact that paper sheets can display two-dimensional images or shaped into three-dimensional objects, lead to novel ways to demonstrate acid–base and other chemical concepts to audiences. For example, paper flowers made from the goldenrod paper will change from yellow to red in basic solutions, to black in very acidic solutions, to off-white in sodium hypochlorite solutions, and to purple-black in iodine solutions.
