Like (*) buffers, these substances often consist of a weak acid and a conjugate base, and can thus be modeled with the Henderson-Hasselbalch equation.
Nitrazine is a substance of this type used in medical contexts, such as testing vaginal fluids for breakage of the amniotic sac or fecal matter for signs of intestinal infections. One of these substances converts from a quinoid structure to a lactone, resulting in a highly conjugated complex. Arnold Beckmann invented a machine that uses a glass electrode to accomplish an analogous function to these substances. Like (*) buffers, these substances often consist of a weak acid and a conjugate base, and can thus be modeled with the Henderson-Hasselbalch equation. They are often used to find equivalence points in titrations, and naturally occurring examples of them include red cabbage and litmus. For 10 points, name these substances that change color in the presence of acids or bases.
Nitrazine is a substance of this type used in medical contexts, such as testing vaginal fluids for breakage of the amniotic sac or fecal matter for signs of intestinal infections.
pH indicators [or acid-base indicators; prompt on "dye(s)"]