Chloride gravimetric determination

Thermal decomposition of perchlorate salts to chloride, followed by the gravimetric determination of the resulting chloride, is a standard method of determining quantitatively the concentration of perchlorates. Any chlorates that are present in the original sample also break down to chloride. Thus results are adjusted to eliminate errors introduced by the presence of any chlorides and chlorates in the original sample. 

The alkah metals are commonly separated from all other elements except chlorine before gravimetric determination. In the absence of other alkaUes, sodium maybe weighed as the chloride or converted to the sulfate and weighed. WeU-known gravimetric procedures employ precipitation as the uranyl acetate of sodium—2inc or sodium—magnesium. Quantitative determination of sodium without separation is frequently possible by emission or atomic-absorption spectrometric techniques. 

Discussion. This gravimetric determination depends upon the separation and weighing as elementary selenium or tellurium (or as tellurium dioxide). Alkali selenites and selenious acid are reduced in hydrochloric acid solution with sulphur dioxide, hydroxylammonium chloride, hydrazinium sulphate or hydrazine hydrate. Alkali selenates and selenic acid are not reduced by sulphur dioxide alone, but are readily reduced by a saturated solution of sulphur dioxide in concentrated hydrochloric acid. In working with selenium it must be remembered that appreciable amounts of the element may be lost on warming strong hydrochloric acid solutions of its compounds if dilute acid solutions (concentration <6M) are heated at temperatures below 100 °C the loss is negligible. 

The gravimetric determination of sulfate can be and is most often used to finish the Eschka and bomb washing methods. The most serious concern is that the barium sulfate precipitated may be extremely fine and difficult to filter. This can be overcome by adding the barium chloride (BaCE) rapidly to the hot solution and stirring the mixture vigorously to obtain a barium sulfate (BaS04) precipitate,... 

Most ionic halides dissolve in water to give hydrated metal ions and halide ions. However, the lanthanide and actinide elements in the +3 and +4 oxidation states form fluorides insoluble in water. Fluorides of Li, Ca, Sr, and Ba also are sparingly soluble, the lithium compound being precipitated by ammonium fluoride. Lead gives a sparingly soluble salt PbCIF, which can be used for gravimetric determination of F . The chlorides, bromides, and iodides of Ag1, Cu1, Hg1, and Pbn are also quite insoluble. The solubility through a series of mainly ionic halides of a... 

Thiopyrylium salts can find application in analytical chemistry. Thus, 2,4,6-triphenylthiopyrylium chloride can be used as a precipitant for the quantitative gravimetric determination of anions (CIO4", 103 , NOj , BF4 ) (87MI3). Thiopyrylium salts can be also used in the spectrophoto-metric determination of bismuth (75URP482648), tellurium (77URP-558856), palladium (77URP558865), and alkyl sulfates (91URP1675746). 

Chlorides were determined by potentiometric titrations performed on distilled water dilutions. Carbonates and bicarbonates were either determined by titration or by calculation from pH measurements. Sulfates were determined by the gravimetric method utilizing BaS04 precipitation. 

Chloride, Chloride is determined gravimetrically as silver chloride. 

Cells may contain text, numbers, or formulas. We will begin by typing some text into the worksheet. Click on cell Al, and type Gravimetric Determination of Chloride followed by the Enter key [ J]. Notice that the active cell is now A2, so you may type Samples [ J]. As you type, the data that you enter appear in the formula bar. If you make a mistake, just click the mouse in the formula bar, and make necessary corrections using the backspace key or the delete key. Continue to type text into the cells of column A as shown below. 

In this exercise, we have learned to calculate a mean, using both the built-in Excel AVERAGE function and a formula of our own design. In Chapter 6, we will use STDEV and other functions to complete our analysis of the data from the gravimetric determination of chloride that we began in Chapter 2. You may now close Excel by typing File/Exit or proceed to Chapter 6 to continue with the spreadsheet exercises. 

As a final exercise, retrieve the spreadsheet that we created in Chapter 3 for the gravimetric determination of chloride, which we called grav chloride.xls. Enter formulas into cells B12—B14 to compute the mean, standard deviation, and the RSD in parts per thousand of the percent chloride in the samples. In this example, multiply the relative standard deviation by 1000 in cell B14. Adjust the decimal point in the results to display the proper number of significant figures. The worksheet below shows the results. Save your worksheet so that you can use it as a model for making laboratory calculations. 

Electrolytic deposition has been nsed for more than a century for the gravimetric determination of metals. In most applications, the metal is deposited on a weighed platinum cathode, and the increase in mass is determined. Some methods use anodic deposition such as the determination of lead as lead dioxide on platinum and of chloride as silver chloride on silver. 

There are many sources of potential error in the gravimetric determination of sulfate as barium sulfate. The greatest source of error concerns the tendency of barium sulfate to carry down and retain the constituents of solvent and precipitant. The most significant source is caused by the adsorption of extraneous (mainly chloride) ions by barium sulfate. 

Precipitation of silver azide from acetate solution and gravimetric determination of the silver as silver azide or silver chloride, or volumetrically by addition of an excess of standard silver nitrate solution and back-titration with standard ammonium thiocyanate using ferric alum as internal indicator. 

Despite the colloidal nature of silver chloride, the gravimetric determination of chloride is one of the most accurate determinations. 

For many years, analytical chemistry relied on chemical reactions to identify and determine the components present in a sample. These types of classical methods, often called wet chanical methods, usually required that a part of the sample be taken and dissolved in a suitable solvent if necessary and the desired reaction carried out. The most important analytical fields based on this approach were volumetric and gravimetric analyses. Acid-base titrations, oxidation-reduction titrations, and gravimetric determinations, such as the determination of silver by precipitation as silver chloride, are all examples of wet chemical analyses. These types of analyses require a high degree of skill and attention to detail on the part of the analyst if accurate and precise results are to be obtained. They are also time consuming, and the demands of today s high-throughput pharmaceutical development labs, forensic labs, commercial environmental labs, and industrial quality control... 

Isothermal method using an oil thermostat. The mixtures were equilibrated for 2-3 hours at 25° and for 30 min at 105°C. At 105°C the samples of saturated solution were drawn into glass tubes and allowed to solidify. The tubes were then weighed and the samples were washed out and analyzed. PoOg was determined gravimetrically using the method of Schmitz (no reference is given). Chloride was determined by the Volhard method. The composition of the solid phases was determined by Schreine-makers method. 

---