71.9 MB (6.2 MB compressed)
6144 x 4088 pixels
52.1 x 34.5 cm ⏐ 20.5 x 13.6 in (300dpi)
RICHARD HUTCHINGS / SCIENCE PHOTO LIBRARY RICHARD HUTCHINGS / SCIENCE PHOTO LIBRARY
Iodine clock reaction using a solution of starch, NaHSO3, and H2SO4 mixed with a solution of KIO3. The iodine clock reaction is a classical chemical clock demonstration experiment to display chemical kinetics in action; it was discovered by Hans Heinrich Landolt in 1886. Two colourless solutions are mixed and at first there is no visible reaction. After a short time delay, the liquid suddenly turns to a shade of dark blue. The iodine clock reaction exists in several variations. In some variations, the solution will repeatedly cycle from colourless to blue and back to colourless, until the reagents are depleted. Full series: JG1765, JG1766, JG1767, JG1768, JG1769, JG1770, JG1771.
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