426:
94:
107:
66:(usually) as a reducing agent is known as iodometric titration since it is used specifically to titrate iodine. The iodometric titration is a general method to determine the concentration of an oxidising agent in solution. In an iodometric titration, a starch solution is used as an indicator since it can absorb the
260:
For simplicity, the equations will usually be written in terms of aqueous molecular iodine rather than the triiodide ion, as the iodide ion did not participate in the reaction in terms of mole ratio analysis. The disappearance of the deep blue color is, due to the decomposition of the iodine-starch
766:
Under strongly acidic solution, the above equilibrium lies far to the right hand side, but is reversed in almost neutral solution. This makes analysis of hexacyanoferrate(III) troublesome as the iodide and thiosulfate decomposes in strongly acidic medium. To drive the reaction to completion, an
689:
content in sample can be determined straight forwardly as described for sulfites, the results are often poor and inaccurate. A better, alternative method with higher accuracy is available, which involves the addition of excess but known volume of standard sodium arsenite solution to the sample,
77:
test with a deep blue hue. This absorption will cause the solution to change its colour from deep blue to light yellow when titrated with standardized thiosulfate solution. This indicates the end point of the titration. Iodometry is commonly used to analyze the concentration of
543:. Iodometry is commonly employed to determine the active amount of hypochlorite in bleach responsible for the bleaching action. In this method, excess but known amount of iodide is added to known volume of sample, in which only the active (
607:
reduce iodine readily in acidic medium to iodide. Thus when a diluted but excess amount of standard iodine solution is added to known volume of sample, the sulfurous acid and sulfites present reduces iodine quantitatively:
732:
is then determined by titrating against standard iodine solution using starch indicator. Note that for the best results, the sulfide solution must be dilute with the sulfide concentration not greater than 0.01 M.
796:
The precipitation occurs in slightly acidic medium, thus avoids the problem of decomposition of iodide and thiosulfate in strongly acidic medium, and the hexacyanoferrate(III) can be determined by iodometry as usual.
110:
Dilute solutions containing iodine–starch complex. Using starch as an indicator can help create a sharper color change at the endpoint (dark blue to colorless). The color above can be seen just before the endpoint is
326:
Some reactions involving certain reductants are reversible at certain pH, thus the pH of the sample solution should be carefully adjusted before performing the analysis. For example, the reaction:
363:
The volatility of iodine is also a source of error for the titration, this can be effectively prevented by ensuring an excess iodide is present and cooling the titration mixture. Strong light,
44:
Note that iodometry involves indirect titration of iodine liberated by reaction with the analyte, whereas iodimetry involves direct titration using iodine as the titrant.
374:
so as to prevent the aerial oxidation of iodide to iodine. Standard iodine solution is prepared from potassium iodate and potassium iodide, which are both
367:
and copper ions catalyse the conversion of iodide to iodine, so these should be removed prior to the addition of iodide to the sample.
827:
425:
547:) can oxidize iodide to iodine. The iodine content and thus the active chlorine content can be determined with iodometry.
872:
840:
370:
For prolonged titrations, it is advised to add dry ice to the titration mixture to displace air from the
887:
550:
The determination of arsenic(V) compounds is the reverse of the standardization of iodine solution with
135:), which have a dark brown color. The triiodide ion solution is then titrated against standard
895:
806:
74:
742:
771:
salt can be added to the reaction mixture containing potassium ions, which precipitates the
415:
266:
8:
443:
48:
27:
677:(This application is used for iodimetry titration because here iodine is directly used)
919:
691:
262:
868:
862:
836:
451:
273:
83:
30:
592:(V) compounds, some tartaric acid is added to solubilize the antimony(III) product.
729:
375:
371:
97:
Color of iodometric titration mixture before (left) and after (right) the end point
79:
914:
604:
551:
539:
Available chlorine refers to chlorine liberated by the action of dilute acids on
87:
34:
93:
908:
544:
411:
772:
540:
106:
136:
832:
272:
The reducing agent used does not necessarily need to be thiosulfate;
128:
863:
Mendham, J.; Denney, R. C.; Barnes, J. D.; Thomas, M. J. K. (2000),
554:, where a known and excess amount of iodide is added to the sample:
589:
447:
289:
686:
680:
600:
595:
430:
419:
364:
285:
281:
277:
295:
At low pH, the following reaction might occur with thiosulfate:
140:
116:
38:
768:
115:
To a known volume of sample, an excess but known amount of
418:, may be titrated against sodium thiosulfate dissolved in
292:(III) salts are commonly used alternatives at pH above 8.
736:
442:
Iodometry in its many variations is extremely useful in
16:
Quantitative analysis of a water-soluble oxidizing agent
119:
is added, which the oxidizing agent then oxidizes to I
446:. Examples include the determination of copper(II),
127:
dissolves in the iodide-containing solution to give
37:
where the appearance or disappearance of elementary
167:Together with reduction potential of thiosulfate:
73:that is released, visually indicating a positive
906:
681:Determination of sulfides and hydrogensulfides
596:Determination of hydrogensulfites and sulfites
867:(6th ed.), New York: Prentice Hall,
784:] + 2 I + 2 K + 2 Zn → 2 KZn[Fe(CN)
424:
105:
92:
858:
856:
854:
852:
429:Iodine standard solution, sealed in an
907:
865:Vogel's Quantitative Chemical Analysis
741:When iodide is added to a solution of
737:Determination of hexacyanoferrate(III)
828:CRC Handbook of Chemistry and Physics
892:National Environmental Methods Index
849:
824:
745:, the following equilibrium exists:
410:Iodine in organic solvents, such as
139:solution to give iodide again using
101:
13:
14:
931:
831:(87th ed.). Boca Raton, FL:
90:in swimming pool water analysis.
437:
880:
818:
207:The overall reaction is thus:
1:
812:
360:is reversible at pH below 4.
825:Lide, David R., ed. (2006).
7:
800:
10:
936:
82:in water samples, such as
754:] + 2 I ⇌ 2 [Fe(CN)
86:in ecological studies or
41:indicates the end point.
459:2 Cu + 4 I → 2 CuI + I
454:, and dissolved oxygen:
433:for iodometric analysis.
888:"Chlorine by Iodometry"
896:U.S. Geological Survey
434:
112:
98:
47:Redox titration using
743:hexacyanoferrate(III)
428:
109:
96:
775:ion quantitatively:
773:hexacyanoferrate(II)
416:carbon tetrachloride
24:iodometric titration
444:volumetric analysis
392:+ 8 I + 6 H → 3 I
49:sodium thiosulphate
807:Iodine–starch test
692:arsenic trisulfide
567:+ 4 H + 4 I ⇌ As
435:
113:
99:
767:excess amount of
694:is precipitated:
452:hydrogen peroxide
376:primary standards
274:stannous chloride
84:oxygen saturation
31:chemical analysis
26:, is a method of
927:
900:
899:
884:
878:
877:
860:
847:
846:
822:
792:
762:
730:arsenic trioxide
724:
673:
671:
670:
667:
654:
653:
650:
640:
638:
637:
634:
621:
620:
617:
605:hydrogensulfites
588:For analysis of
584:
535:
530:2 Mn + 2 I → I
526:
506:
485:
475:
474:
471:
463:
406:
400:
399:
396:
391:
390:
387:
372:Erlenmeyer flask
356:
322:
312:
311:
308:
248:
246:
245:
242:
233:
232:
229:
220:
219:
216:
198:
197:
196:
193:
184:
183:
180:
158:
156:
155:
152:
102:Basic principles
80:oxidizing agents
72:
65:
935:
934:
930:
929:
928:
926:
925:
924:
905:
904:
903:
886:
885:
881:
875:
861:
850:
843:
823:
819:
815:
803:
791:
787:
783:
779:
761:
757:
753:
749:
739:
722:
718:
714:
710:
706:
702:
698:
683:
668:
665:
664:
662:
658:
651:
648:
647:
645:
635:
632:
631:
629:
625:
618:
615:
614:
612:
598:
582:
578:
574:
570:
566:
562:
558:
552:sodium arsenite
533:
529:
525:
521:
517:
513:
509:
504:
500:
496:
492:
488:
483:
479:
472:
469:
468:
466:
462:
458:
440:
404:
397:
394:
393:
388:
385:
384:
382:
354:
350:
346:
342:
338:
334:
330:
320:
316:
309:
306:
305:
303:
299:
256:= +0.46 V)
255:
243:
240:
239:
237:
230:
227:
226:
224:
217:
214:
213:
211:
203:= +0.08 V)
194:
191:
190:
188:
181:
178:
177:
175:
171:
163:= +0.54 V)
153:
150:
149:
147:
134:
126:
122:
104:
88:active chlorine
71:
67:
64:
60:
56:
52:
35:redox titration
17:
12:
11:
5:
933:
923:
922:
917:
902:
901:
879:
873:
848:
841:
816:
814:
811:
810:
809:
802:
799:
794:
793:
789:
785:
781:
764:
763:
759:
755:
751:
738:
735:
726:
725:
720:
716:
712:
708:
704:
700:
682:
679:
675:
674:
660:
656:
642:
641:
627:
623:
597:
594:
586:
585:
580:
576:
572:
568:
564:
560:
537:
536:
531:
527:
523:
519:
515:
511:
507:
502:
498:
494:
490:
486:
481:
477:
464:
460:
439:
436:
408:
407:
402:
358:
357:
352:
348:
344:
340:
336:
332:
324:
323:
318:
314:
301:
258:
257:
253:
235:
222:
205:
204:
186:
173:
165:
164:
132:
124:
120:
103:
100:
69:
62:
58:
54:
15:
9:
6:
4:
3:
2:
932:
921:
918:
916:
913:
912:
910:
897:
893:
889:
883:
876:
874:0-582-22628-7
870:
866:
859:
857:
855:
853:
844:
842:0-8493-0487-3
838:
834:
830:
829:
821:
817:
808:
805:
804:
798:
780:2 [Fe(CN)
778:
777:
776:
774:
770:
750:2 [Fe(CN)
748:
747:
746:
744:
734:
731:
697:
696:
695:
693:
690:during which
688:
685:Although the
678:
644:
643:
611:
610:
609:
606:
602:
593:
591:
557:
556:
555:
553:
548:
546:
545:electrophilic
542:
528:
508:
487:
476:+ 6 I → 3 I
465:
457:
456:
455:
453:
449:
445:
432:
427:
423:
421:
417:
413:
412:diethyl ether
381:
380:
379:
377:
373:
368:
366:
361:
329:
328:
327:
298:
297:
296:
293:
291:
287:
283:
279:
275:
270:
268:
264:
252:
210:
209:
208:
202:
185:+ 2 e ⇌ 2 S
170:
169:
168:
162:
157:+ 2 e ⇌ 3 I
146:
145:
144:
142:
138:
130:
118:
108:
95:
91:
89:
85:
81:
76:
75:iodine-starch
50:
45:
42:
40:
36:
32:
29:
25:
21:
891:
882:
864:
826:
820:
795:
765:
740:
727:
684:
676:
672:+ 3H + + 2 I
599:
587:
549:
541:hypochlorite
538:
514:O + 4 Mn(OH)
441:
438:Applications
409:
369:
362:
359:
325:
313:+ 2 H → SO
294:
271:
265:, marks the
259:
250:
206:
200:
166:
160:
114:
46:
43:
23:
22:, known as
19:
18:
728:The excess
639:+ 2 H + 2 I
522:→ 4 Mn(OH)
497:+ 2 I → I
355:+ 2 H + 2 I
288:(III), and
143:indicator:
137:thiosulfate
909:Categories
813:References
480:+ Cl + 3 H
28:volumetric
920:Titration
833:CRC Press
467:6 H + ClO
267:end point
263:clathrate
129:triiodide
20:Iodometry
801:See also
711:S → As
663:O → SO
630:O → SO
601:Sulfites
590:antimony
448:chlorate
290:antimony
282:sulfides
278:sulfites
254:reaction
111:reached.
687:sulfide
489:2 H + H
431:ampoule
420:acetone
365:nitrite
347:O → H
317:+ S + H
286:arsenic
131:ions (I
915:Iodine
871:
839:
534:+ 2 Mn
141:starch
39:iodine
788:] + I
758:] + I
719:+ 3 H
707:+ 3 H
579:+ 2 H
575:+ 2 I
501:+ 2 H
401:+ 3 H
247:+ 3 I
221:+ 2 S
869:ISBN
837:ISBN
769:zinc
603:and
414:and
234:→ S
33:, a
659:+ H
655:+ I
646:HSO
626:+ H
622:+ I
518:+ O
510:2 H
351:AsO
343:+ H
339:+ I
335:AsO
123:. I
911::
894:.
890:.
851:^
835:.
699:As
666:2−
633:2−
616:2−
613:SO
559:As
450:,
422:.
383:IO
378::
307:2−
284:,
280:,
276:,
269:.
241:2−
228:2−
192:2−
179:2−
53:Na
51:,
898:.
845:.
790:2
786:6
782:6
760:2
756:6
752:6
723:O
721:2
717:3
715:S
713:2
709:2
705:3
703:O
701:2
669:4
661:2
657:2
652:3
649:−
636:4
628:2
624:2
619:3
583:O
581:2
577:2
573:3
571:O
569:2
565:5
563:O
561:2
532:2
524:3
520:2
516:2
512:2
505:O
503:2
499:2
495:2
493:O
491:2
484:O
482:2
478:2
473:3
470:−
461:2
405:O
403:2
398:3
395:−
389:3
386:−
353:4
349:3
345:2
341:2
337:3
333:3
331:H
321:O
319:2
315:2
310:3
304:O
302:2
300:S
251:E
249:(
244:6
238:O
236:4
231:3
225:O
223:2
218:3
215:−
212:I
201:E
199:(
195:3
189:O
187:2
182:6
176:O
174:4
172:S
161:E
159:(
154:3
151:−
148:I
133:3
125:2
121:2
117:I
70:2
68:I
63:3
61:O
59:2
57:S
55:2
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