940:
617:
Once all the thiosulfate is consumed the iodine may form a complex with the starch. Potassium persulfate is less soluble (cfr. Salters website) while ammonium persulfate has a higher solubility and is used instead in the reaction described in examples from Oxford
University.
20:
226:
concentration), or increasing the concentration of iodide or hydrogen peroxide will shorten the time. Adding more thiosulfate will have the opposite effect; it will take longer for the blue colour to appear.
21:
23:
24:
68:. 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 due to the formation of a
986:
1000:
22:
1125:
480:
When the bisulfite is fully consumed, the iodine will survive (i.e., no reduction by the bisulfite) to form the dark blue complex with starch.
72:. In some variations, the solution will repeatedly cycle from colorless to blue and back to colorless, until the reagents are depleted.
215:
Anything that accelerates the first reaction will shorten the time until the solution changes color. Decreasing the pH (increasing
386:
This first step is the rate determining step. Next, the iodate in excess will oxidize the iodide generated above to form iodine:
858:
1120:
1007:
1130:
907:
627:
1140:
980:
882:
690:
45:
1100:
952:
493:
208:. Once the thiosulfate ion has been exhausted, this reaction stops and the blue colour caused by the
853:
848:
497:
205:
826:
is the time it takes for the autocatalytic process to start after which the concentration of free
968:
512:
93:
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1063:
489:
81:
41:
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960:
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89:
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908:"Ueber die Zeitdauer der Reaction zwischen Jodsäure und schwefliger Säure [Part 2]"
626:
An experimental iodine clock sequence has also been established for a system consisting of
143:
In the second, fast reaction, iodine is reconverted to two iodide ions by the thiosulfate:
1135:
682:
635:
631:
956:
843:
264:
37:
778:
when newly generated iodous acid also converts chlorate in the fastest reaction step:
1114:
1061:
André P. Oliveira and
Roberto B. Faria (2005). "The chlorate-iodine clock reaction".
972:
775:
686:
326:
201:
85:
48:
in 1886. The iodine clock reaction exists in several variations, which each involve
340:
ion is generated by the following slow reaction between the iodate and bisulfite:
910:[On the duration of the reaction between iodic acid and sulfurous acid].
885:[On the duration of the reaction between iodic acid and sulfurous acid].
313:
Similar to thiosulfate case, when cysteine is exhausted, the blue color appears.
964:
731:
209:
69:
515:
is used to reduce iodine back to iodide before the iodine can complex with the
325:
ion (for instance potassium iodate) to which an acidified solution (again with
1105:
923:
898:
193:
After some time the solution changes color to a very dark blue, almost black.
641:
427:
However, the iodine is reduced immediately back to iodide by the bisulfite:
100:
is added. There are two reactions occurring simultaneously in the solution.
1083:
263:
The iodine produced in the first reaction is reduced back to iodide by the
237:
Iodide from potassium iodide is converted to iodine in the first reaction:
883:"Ueber die Zeitdauer der Reaction zwischen Jodsäure und schwefliger Säure"
941:"Clock Reaction Revisited: Catalyzed Redox Substrate-Depletive Reactions"
231:
1075:
730:
Chlorate consumption is accelerated by reaction of hypoiodous acid to
831:
827:
649:
645:
516:
508:
504:
337:
322:
197:
97:
65:
57:
53:
49:
501:
61:
18:
267:, cysteine. At the same time, cysteine is oxidized into cystine.
939:
Limpanuparb, T.; Ruchawapol, C.; Sathainthammanee, D. (2019).
196:
When the solutions are mixed, the second reaction causes the
1001:"Experiment 6: THE RATE LAWS OF AN IODINE CLOCK REACTION"
204:, and only a small amount of iodine is present in the
230:
Aside from using sodium thiosulfate as a substrate,
1106:
Sodium bisulfite variation with a high-speed camera
1033:"Kinetics of the Persulfate-iodide Clock Reaction"
638:that takes place through the following reactions.
103:In the first, slow reaction, iodine is produced:
1040:2nd/3rd Year Physical Chemistry Practical Course
912:Berichte der Deutschen Chemischen Gesellschaft
887:Berichte der Deutschen Chemischen Gesellschaft
16:Experiment to show chemical kinetics in action
519:to form the characteristic blue-black color.
8:
985:: CS1 maint: multiple names: authors list (
28:Iodine clock reaction (persulfate variation)
321:An alternative protocol uses a solution of
202:consumed much faster than it is generated
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549:
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452:
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173:
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128:
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109:
870:
978:
80:This method starts with a solution of
7:
681:Chlorate ion oxidizes iodide ion to
40:demonstration experiment to display
88:. To this a solution containing
14:
44:in action; it was discovered by
1126:Chemistry classroom experiments
644:is present in equilibrium with
1:
945:Journal of Chemical Education
830:falls rapidly as observed by
210:iodine – starch complex
64:reagents in the presence of
1101:Hydrogen peroxide variation
965:10.1021/acs.jchemed.8b00547
76:Hydrogen peroxide variation
1157:
924:10.1002/cber.188702001173
899:10.1002/cber.188601901293
488:This clock reaction uses
1031:Hugh Cartwright (2006).
859:Briggs–Rauscher reaction
734:and more chlorous acid:
70:triiodide–starch complex
832:UV–visible spectroscopy
628:iodine potassium-iodide
29:
691:rate-determining step
568:And is then removed:
522:Iodine is generated:
56:ion, free iodine, or
46:Hans Heinrich Landolt
34:iodine clock reaction
27:
906:Landolt, H. (1887).
881:Landolt, H. (1886).
648:anion and molecular
484:Persulfate variation
1070:(51): 18022–18023.
1042:. Oxford University
957:2019JChEd..96..812L
854:Chemical oscillator
849:Old Nassau reaction
498:ammonium persulfate
206:dynamic equilibrium
822:In this clock the
622:Chlorate variation
513:Sodium thiosulfate
336:In this protocol,
234:can also be used.
94:sodium thiosulfate
30:
1121:Chemical kinetics
1076:10.1021/ja0570537
1064:J. Am. Chem. Soc.
82:hydrogen peroxide
42:chemical kinetics
25:
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1006:. Archived from
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902:
893:(1): 1317–1365.
875:
824:induction period
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331:sodium bisulfite
317:Iodate variation
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90:potassium iodide
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1131:Clock reactions
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683:hypoiodous acid
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636:perchloric acid
632:sodium chlorate
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36:is a classical
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5:
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1095:External links
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1090:
1089:
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1023:
992:
951:(4): 812–818.
931:
929:
928:
918:(1): 745–760.
903:
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844:Clock reaction
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265:reducing agent
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38:chemical clock
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10:
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3:
2:
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1027:
1024:
1013:on 2018-05-17
1009:
1002:
996:
993:
988:
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966:
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954:
950:
946:
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914:(in German).
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889:(in German).
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780:
779:
777:
776:autocatalysis
737:
736:
735:
733:
696:
695:
694:
692:
688:
687:chlorous acid
684:
655:
654:
653:
651:
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327:sulfuric acid
324:
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203:
199:
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86:sulfuric acid
83:
75:
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71:
67:
63:
59:
55:
51:
47:
43:
39:
35:
1141:Thiosulfates
1067:
1062:
1056:
1044:. Retrieved
1039:
1026:
1015:. Retrieved
1008:the original
995:
981:cite journal
948:
944:
934:
915:
911:
890:
886:
873:
821:
773:
729:
680:
640:
625:
616:
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521:
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312:
269:
262:
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214:
195:
192:
142:
102:
79:
33:
31:
732:iodous acid
1115:Categories
1017:2018-04-30
865:References
333:is added.
973:104370691
642:Triiodide
494:potassium
244:+ 2 H + H
212:appears.
60:ion) and
52:species (
1084:16366551
1046:25 March
838:See also
507:ions to
232:cysteine
953:Bibcode
502:oxidize
1136:Iodine
1082:
971:
828:iodine
650:iodine
646:iodide
517:starch
509:iodine
505:iodide
490:sodium
338:iodide
323:iodate
310:+ 2 H
200:to be
198:iodine
98:starch
96:, and
66:starch
58:iodate
54:iodide
50:iodine
1036:(PDF)
1011:(PDF)
1004:(PDF)
969:S2CID
877:See:
774:More
457:→ 2
409:→ 3
329:) of
282:S + I
256:+ 2 H
62:redox
1080:PMID
1048:2018
987:link
814:HClO
766:HClO
722:HClO
712:+ 2
685:and
634:and
594:→ 2
578:+ 2
553:+ 2
473:+ 2
416:+ 3
405:+ 6
401:+ 5
371:+ 3
355:+ 3
306:+ 2
186:+ 2
132:+ 2
121:+ 2
117:+ 2
84:and
32:The
1072:doi
1068:127
961:doi
920:doi
895:doi
795:HIO
783:ClO
759:HIO
751:HOI
739:ClO
718:HOI
698:ClO
500:to
496:or
463:HSO
439:HSO
373:HSO
367:→
357:HSO
286:→ C
270:2 C
252:→ I
1117::
1078:.
1038:.
983:}}
979:{{
967:.
959:.
949:96
947:.
943:.
916:20
891:19
834:.
812:+
802:IO
800:→
793:+
764:+
757:→
753:+
749:+
720:+
716:→
708:+
693::
674:+
667:⇌
652::
630:,
607:2−
598:+
587:2−
558:2−
555:SO
546:→
539:2−
530:+
526:2
511:.
492:,
461:+
449:+
437:+
391:IO
345:IO
292:12
278:NO
260:O
240:2
179:2−
170:→
163:+
156:2−
147:2
125:→
92:,
1086:.
1074::
1050:.
1020:.
989:)
975:.
963::
955::
926:.
922::
901:.
897::
816:2
808:3
805:−
797:2
789:3
786:−
768:2
761:2
755:H
745:3
742:−
724:2
714:H
710:I
704:3
701:−
676:I
671:2
669:I
663:3
660:−
657:I
610:6
604:O
602:4
600:S
596:I
590:3
584:O
582:2
580:S
575:2
573:I
561:4
550:2
548:I
542:8
536:O
534:2
532:S
528:I
475:H
469:4
466:−
459:I
455:O
453:2
451:H
445:3
442:−
434:2
432:I
422:O
420:2
418:H
413:2
411:I
407:H
403:I
397:3
394:−
379:4
376:−
369:I
363:3
360:−
351:3
348:−
308:I
304:2
302:S
300:4
298:O
296:2
294:N
290:H
288:6
284:2
280:2
276:7
274:H
272:3
258:2
254:2
250:2
248:O
246:2
242:I
217:H
188:I
182:6
176:O
174:4
172:S
167:2
165:I
159:3
153:O
151:2
149:S
138:O
136:2
134:H
129:2
127:I
123:H
119:I
114:2
112:O
110:2
108:H
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