Applications involving the iodide ion

MICROCHEMICAL

13, 147-154

JOURNAL

Applications II. Microdetermination and

Periodate

Involving

the Iodide

Ion

of Oxidizing

Agents

Use of Potassium

as Primary

Standards

for Mercury(H)

H. KHALIFA Faculty

( 1968)

lodate

AND B. ATEYA

of Science, Cairo University,

Gim,

U.A.R.

Received Awgust 21,1967 INTRODUCTION

Regarding oxalate as primary standard for both cerium( IV) and permanganate, it was reported that exact results were obtained only at high temperature (IO, 11)) in presence of indicator (5)) by running a blank or by using certain catalysts (5, IO, 11). However, air oxidation and loss of carbon monoxide (5, p. 51) are reported as being possible sources of error. The arsenite method as applied to standardization of cerium( IV ) and permanganate involves, as well, some ,of the above tedious precautions (5, p. 131; 8; 9). The acetone method (6) using potassium iodide as primary standard for cerium( IV), permanganate and dichromate gives low results owing to partial reduction of the oxidant with acetone and iodoacetone. The potentiometric method using these oxidants as titrants for iodide (4) cannot be used in the microgram range. The use of Mohr’s salt as primary standard (3) lost favor due to inherent contamination with manganese( II), zinc, and magnesium (7). The method of Caraway (2) involves errors amounting to 2.7%.

Most of the literature refers to iodate, periodate and bromate as primary standards. Very recently Agarwal (1) applied thiourea as titrant for potassium iodate in 2 N sulfuric acid with starch as indicator. The mechanism of the process involves reduction of iodate to iodide, reaction of iodide with iodate liberating iodine which is reduced to iodide with thiourea. Even though he reported high accuracy, yet liberation of iodine in iodide-free medium may be a source of error. The present potentiometric method as applied to the determination of all the above oxidants has several advantages, namely, applicability 147

148

KHALIFA

ANDATEYA

to all oxidants over a wide range of concentration, and high accuracy and precision. EXPERIMENTAL

simplicity,

rapidity,

METHOD

The water used in this investigation was always twice distilled from all glass equipment. The chemicals were of the highest purity available. These were nitrates of iron(III), mercury(II) and copper(D); iodide, permanganate, chromate, dichromate, bromate, iodate, and periodate of potassium; thiosulfate, sulfite, oxalate, and arsenate of sodium; ceric ‘oxide; arsenious oxide; starch; iodine; sulfuric acid; and ethylenediaminetetraacetic acid (EDTA) . Solutions The 0.0544 M Hg( II) solution was prepared from mercuric nitrate and standardized potentiometrically against standard EDTA and potassium iodide solutions using silver amalgam as indicator electrode. The iodide solutions were 0.054 and 0.0496 M as standardized against the mercuric solution, The 0.082 IV permanganate solution was prepared by a recommended procedure and standardized against arsenious oxide, standard thiosulfate and oxalate, (by adding a known volume to the acidified solution ,of 0.200 g of oxalate, heating to 60°C and titrating the resulting colorless solution with permanganate ). The 0.1506 IV chromate solution was prepared by direct weighing from dried A.R. sample and checked iodometrically. The 0.100 N dichromate solution was prepared from a recrystallized sample and standardized iodometrically. The 0.0359 iV cerium( IV) solution was prepared by treating ceric oxide (Hopkin and Williams Ltd.) with hot concentrated sulfuric acid, separating by decantation the insoluble ceric sulfate residue, dissolving it in the requisite volume of water and filtering if necessary. The 0.01444 M (0.072 N) iodate solution was prepared by direct weighing from A. R. sample (3.082 g/liter). The 0.014285 M (0.1 N) potassium periodate solution was 3.286 g/liter. The 0.12214 iV bromate solution was 3.400 g/liter. Lower concentrations of the above solutions were prepared by accurate dilution.

IODIDE

ION

149

Cell and Equipment The titration cell consisted of a 250~ml beaker fitted with a rubber cover holding a mechanical stirrer, a 5-ml l/50 graded burette with its tip immersed into the solution, a salt bridge, and silver amalgam electrode. The amalgam electrode and a saturated calomel electrode are connected to a three-cell Cambridge potentiometer No. L. 28795 with potential range from 0 to 1800 mV.

Procedures A. Determination of a given oxidant involved addition of a known volume of oxidant (OS-5 ml) to excess iodide solution (8-12 ml) made about 2 or 0.2 iV in respect of sulfuric acid with macro- and micro-amounts, respectively, followed by titration of excess iodide with Hg( II) using ,silver amalgam as indicator electrode. With chromate and dichromate the solution should always be at least 2 N in acid before titration. B. An alternative procedure for macro- and micro-determination of iodate and periodate involved addition of a known volume of oxidant to a mixture of 10 ml of 2 IV sulfuric acid and about 0.1 g of solid sulfite followed by titration of the resulting iodide as mentioned above. RESULTS

AND DISCUSSION

Tables 1 and 2 list representative results of macro- and micro-determinations of permanganate, chromate, dichromate, bromate, and cerium( IV); the data indicate that the present method is extremely reliable. With bromate the somewhat smaller potential inflections are attributed to the influence of bromide resulting from reduction of bromate with iodide, on the potential set by the silver amalgam electrode. However, the breaks are still sharp enough to detect the correct end points. Relatively large amounts of Fe( III ), Cu( II) and As(V) do not interfere with the determination of permanganate, chromate, and dichromate. This phenomenon is interpreted by considering the following possible equilibria. Fe3+ + I- + Fez+ + # 12, cu2+ + I- * cu+ + K IS, AsO,- + 21- + 2H+ * AsOz- + Ia + HzO,

150

KHALIFA

AND

TABLE

ATEXA

1

MACRODETERMINATIONS

a

Vol. No.

Taken (mes)

Found (mes)

titrated (ml)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

0.32800 0.24600 0.16400 0.08200 0.06150 0.30114 0.15057 0.09033 0.06022 0.03011 0.40000 0.30000 0.25920 0.20000 0.10368 0.36630 0.24420 0.12214 0.10023 0.06109 0.25130 0.17950 0.10770 0.07180 0.03590

0.32832 0.24609 0.16520 0.08208 0.06135 0.29802 0.14909 0.09120 0.06048 0.03024 0.40060 0.29760 0.25975 0.20068 0.10480 0.36849 0.24672 0.12268 0.10060 0.06098 0.24948 0.17951 0.10680 0.07209 0.03591

25 25 30 30 16 32 35 25 20 20 50 25 25 20 22 20 18 20 20 20 25 18 15 15 12

a l-5 permanganate, 1, 7, and 11 detd. in presence of 42 mg of Fe( III), of Cu( II), and 39 mg of As(V); 6-10 chromate; 11-15 dichromate; bromate; 20-25 Ce( IV); detd. with 0.0544 it4 Hg( II) and 0.0540 M I-.

mV per 0.1 ml titrant 291 291 288 265 268 278 253 273 283 283 270 278 284 302 295 110 122 146 169 184 327 284 292 292 321 48 mg 16-20

from which, even though it is apparent that the above elements tend to interfere, yet the mercuric ions added as titrant continuously consume iodide, and hence the above equilibria will always be shifted to the left-hand side. Table 3 lists representative results of macro- and microdeterminations of iodate and periodate by procedure A. Table 4 contains results

IODIDE

TABLE

2

MICRODETERMINATIONS

No.

Taken (mes)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

0.02050 0.01230 0.00820 0.00410 0.00205 0.02408 0.01806 0.01204 0.00602 0.05184 0.05000 0.02592 0.01555 0.05000 0.02500 0.02000 0.01500 0.00500 0.02872 0.02154 0.00719

151

ION

Found Cm4 0.02045 0.01218 0.00822 0.00408 0.002045 0.02389 0.01813 0.01210 0.006025 0.05200 0.04960 0.02592 0.01565 0.05050 0.02460 0.02003 0.01506 0.00500 0.02876 0.02152 0.00709

a

Vol. titrated (ml) 18 16 14 15 15 20 22 18 16 20 12 12 12 15 12 18 16 13 20 16 16

mV per 0.1 ml titrant 194 228 254 235 233 267 228 261 259 278 308 308 300 175 278 170 161 214 268 208 210

a 1-5 permanganate, detd. with 0.010 M Hg( II); 6-9 chromate, lo-13 dichromate, 6-13 detd. with 0.01388 M Hg( II); 14-18 bromate, 19-21 cerium( IV), 14-21 detd. with 0.00985 M Hg( II); iodide was always 0.01484 M; 4,8, and 13 detd. in presence of 14 mg of Fe(III), 16 mg of Cu(I1) and 13 mg of As(V).

of macro- and microdeterminations of iodate and periodate using procedure B. The data in Tables 3 and 4 show that by procedures A and B, respectively, iodate and periodate can be determined with high accuracy and precision. Furthermore, procedure B exhibits high selectivity, and can be applied to the determination of as little as 100 pg of Hg( II) with fair accuracy.

152

KHALIFA

AND

TABLE DETERMINATIONS

ATIXYA

3

BY PROCEDURE

Aa

Vol. No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 18 17

Taken (med 0.72000 0.21600 0.14400 0.05760 0.04320 0.00864 0.00288 0.001152 0.50000 0.30000 0.20000 0.10200 0.10000 0.07650 0.02040 0.00510 0.00255

Found (mes) 0.72310 0.21600 0.14334 0.05803 0.04303 0.00866 0.002875 0.001149 0.50165 0.29769 0.19818 0.10232 0.10071 0.07650 0.02047 0.00507 0.002537

titrated (ml) 40 18 20 20 18 13 12 15 25 18 17 17 13 16 14 12 13

mV per 0.1 ml titrant 259 289 263 210 211 135 135 148 273 285 272 308 298 275 262 273 250

a l-8 iodate; Q-17 periodate; 1-3, Q-14 detd. with 0.0544 M Hg( II) and 0.0540 M I-; 4, 5 detd. with 0.0098 M Hg( II); 15-17 with 0.00985 M Hg( II); 4, 5, 15, 16, and 17 with 0.01484 A4 I-; and 6-Q with 0.00196 M Hg(I1) and 0.00297 M I-.

IODIDE

TABLE DETERMINATIONS

153

IOiX

4

BY PROCEDURE

No.

Taken (mM)

Found (mM)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

0.43200 0.28800 0.21600 0.07776 0.05760 0.04320 0.02880 0.02016 0.00576 0.00432 0.00152 0.35712 0.28570 0.21427 0.14285 0.09999 0.03591 0.02873 0.01795 0.00718 0.00583 0.003645 0.001458

0.42870 0.28940 0.21598 0.07812 0.05774 0.04327 0.02881 0.02009 0.005684 0.004257 0.001142 0.35501 0.28505 0.21431 0.14285 0.09988 0.03578 0.02864 0.01806 0.00721 0.00578 0.003649 0.001447

a l-11 iodate; 12-23 periodate; 1-3, 12-16 with 0.0098 M Hg(I1); 9-11 with 0.00196 Hg( II); and 21-23 with 0.001088 M Hg( II).

Ba Vol. titrated

mV per 0.1 ml titrant

(ml) 40 30 25 37 30 25 20 17 15 13 12 32 27 22 17 20 23 20 15 12 20 12 10 detd. with Hg(I1);

M

0.0544 17-20

323 346 336 156 118 156 116 201 153 123 148 273 314 317 340 311 125 167 191 251 164 190 210

M with

Hg(I1); 0.00544

4-8

M

SUMMARY A new method is given for the accurate microdetermination of a variety of oxidizing agents, including permanganate, chromate, dichromate, iodate, periodate, bromate and cerium( IV), by adding the oxidant to a known excess of standard iodide solution properly acidified with sulfuric acid, followed by titrating excess iodide with mercury( II) potentiometrically using a silver amalgam as indicator electrode. The results are quite satisfactory and the end points are well defined with very sharp potential breaks. Permanganate, chromate, and dichromate were determined with fair accuracy and precision in presence of iron( III), copper( II)

154

KHALIFA

AND

ATJZYA

and arsenic ( V ) . Further, it was found that the stoichiometry of the reaction between iodide and the above oxidants is stiI1 maintained even with very low concentrations. Another interesting and very sensitive method is investigated for the microdetermination of iodate and periodate involving reduction with suIfurous acid, prior to potentiometric titration of the resulting iodide as mentioned above. The results indicate that potassium iodate and periodate are excellent primary standards for mercury( II). REFERENCES 1.

2. 3. 4. 5.

6. 7. 8.

9. 10. Il.

R. P. AND GHOSH, S. K., Applications of thiourea in analytical chemistry, B-Determination of potassium iodate. Chim. anal. (Paris) 48 (3), 141-142 (1966). CARAWAY, K. P., AND OESPER, R. E., Ferrous ethylene diamine sulphate as an oxidimetric standard. J. Chem. E&c. 24,235 (1947). FURMAN, N. H., AND WALLACE, J. H., Application of ceric sulphate in volumetric analysis. J. Am. Chem. Sot. 52, 1449, 2346 ( 1939). HINDRIXON, W. S., the electrotitration of hydroiodic acid and its use as standard in oxidimetry. J. Am. Chem. Sot. 43, 14, 858 ( 1921). KOLTHOFF, I. M., AND BELCHER, “Volumetric Analysis,” Vol. 3. Wiley ( Interscience ) , New York, 1957. KOLTHOFF, I. M., AND LAITINEN, H. A., The standardization of strong oxidizing agents with potassium iodide by the acetone method. J. Am. Chem. Sot. 61, 1690 ( 1939). KOLTHOFF, I. M., AND SANDELL, E. B., “Text Book of Quantitative Inorganic Analysis,” p. 595. Macmillan, New York, 1943. M~IZLER, D. E., MEYRS, J. R., AND SWIFT, H. E., Use of iodine-monochloride in standardization of permanganate solutions with arsenious oxide. Id. Eng. Chem., And. Ed. 16, 625 (1944). WALDEN, G. H., JR., HAMMETT, L. P., AND CHAPMAN, R. R., PhenanthroIineferrous ion: A reversible oxidation-reduction indicator of high potential and its use in oxidimetric titrations. .I. Am. C&m. Sot. 55,2649 (1933). WATSON, J. P., Manganese sulphate as a catalyst in ceric sulphate titrations. Analyst 76, 177 ( 1951). WILLARD, H. H., AND YOUNG, P., Ceric sulphate as a volumetric oxidizing agent. J. Am. Chem. Sot. 50, 1322 (1922). AGARWAL,