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If dependence is being placed upon the volumetric method, it is advisable to lengthen the duration of the test considerably, and if possible to measure the feed-water evaporated at the same time. Such a course, however, would necessitate little change, and none of a radical nature, from the arrangement described.
It is, in general, true that oxidizable substances are determined by !direct! titration, while oxidizing substances are determined by !indirect! titration. The important oxidizing agents employed in volumetric solutions are potassium bichromate, potassium permangenate, potassium ferricyanide, iodine, ferric chloride, and sodium hypochlorite.
The comparison of the acid and alkali solutions was made, using methyl orange as an indicator, while the titration of the oxalic acid is made with the use of phenolphthalein. In the oxidation processes of volumetric analysis standard solutions of oxidizing agents and of reducing agents take the place of the acid and alkali solutions of the neutralization processes already studied.
The liberated iodine is then determined by titration with sodium thiosulphate, as described on page 78. The titration of iodine against sodium thiosulphate, with starch as an indicator, may perhaps be regarded as the most accurate of volumetric processes. The fundamental reaction upon which iodometric processes are based is the following: I + 2 Na S O > 2 NaI + Na S O .
The processes of volumetric analysis are easily classified, according to their character, into: I. NEUTRALIZATION METHODS; such, for example, as those of acidimetry and alkalimetry. II. OXIDATION PROCESSES; as exemplified in the determination of ferrous iron by its oxidation with potassium bichromate.
!Answers!: Acid; 1.86 cc. alkali. In preparing an alkaline solution for use in volumetric work, an analyst, because of shortage of chemicals, mixed exactly 46.32 grams of pure KOH and 27.64 grams of pure NaOH, and after dissolving in water, diluted the solution to exactly one liter. How many cubic centimeters of 1.022 N hydrochloric acid are necessary to neutralize 50 cc. of the basic solution?
This brings us at once to the consideration of that theory which probably has held our attention for the longest period of time, i. e., the volumetric theory. According to it, the normal intra-ocular tension depends on the volume of fluids within the eyeball.
Two burettes, one at least of which should have a glass stopper, are required throughout the volumetric work. Both burettes should be calibrated by the student to whom they are assigned. Record the weight in the notebook. Do not attempt to stop exactly at the 10 cc. mark, but do not vary more than 0.1 cc. from it.
An example will make clear the distinction between these two types of analysis. This is a !volumetric! process, and is equivalent to weighing without the use of a balance. They are particularly useful when many determinations of the same sort are required.
Such hydrolytic processes as the above are of great importance in analytical chemistry, especially in the understanding of the action of indicators in volumetric analysis. The impelling force which causes an element to pass from the atomic to the ionic condition is termed !electrolytic solution pressure!, or ionization tension.
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