Chloride gravimetric analysis

This experiment describes the use of a fractional factorial design to examine the effects of volume of HNO3, molarity of AgN03, volume of AgN03, digestion temperature, and composition of wash water on the gravimetric analysis for chloride. 

Tetraphenylarsonium chloride (107,108) has also been used for the precipitation of the perchlorate ion in gravimetric analysis. 

The heavy metal salts, ia contrast to the alkah metal salts, have lower melting points and are more soluble ia organic solvents, eg, methylene chloride, chloroform, tetrahydrofiiran, and benzene. They are slightly soluble ia water, alcohol, ahphatic hydrocarbons, and ethyl ether (18). Their thermal decompositions have been extensively studied by dta and tga (thermal gravimetric analysis) methods. They decompose to the metal sulfides and gaseous products, which are primarily carbonyl sulfide and carbon disulfide ia varying ratios. In some cases, the dialkyl xanthate forms. Solvent extraction studies of a large number of elements as their xanthate salts have been reported (19). 

Properties. The Qf of the anhyd salt was calcd to be — 179kcal/mole (Ref 8), and of the aq soln to be — 173.94kcal/mole (Ref 6). Effect of heat Marvin Woolaver found by thermo-gravimetric analysis that Ca perchlorate starts to decomp at 220° and decomps rapidly at 400° to give Ca oxide, Ca chloride, and perchloric ac (Ref 5). Chudinov in the USSR states thatit decomps betw 320 and 455° with the formn of Ca oxide, Ca chloride, Cl, and O (Ref 7). Solubility it is sol in w and most org solvs except eth (Ref 3)... 

Theory Gravimetric analysis of proguanil hydrochloride involves the precipitation of the proguanil-cupric complex that results on the addition of ammoniacal cupric chloride solution to a solution of proguanil hydrochloride. The reaction can be expressed by the following equation ... 

As an example, gravimetric analysis can be used to determine the amount of water in hydrated barium chloride. 

Water of crystaUization in hydrated salts can be measured by thermo-gravimetric analysis. Zinc can be analyzed in an aqueous solution by AA or ICP. Sulfate can be identified by precipitation with barium chloride solution or by ion chromatography. The zinc content in the heptahydrate is determined by AA, ICP and other instrumental methods. 

Gravimetric analysis for chloride in wastewaters does not give accurate results at concentrations below 100 mg/L. This method is rarely applied in routine environmental analysis because it is lengthy and rigorous. 

Figure 18.8. Thermal gravimetric analysis-mass spectroscopy characterization of poly(vinyl chloride). Reproduced fromTA Instruments, Inc. (1995a), by permission of TA Instruments, Inc.

The chlorine content of Polymer Fractions I, II, and III was determined by gravimetric analysis and found in all cases to be within 1% of the value for undegraded poly (vinyl chloride). (Since it was difficult to remove the last traces of solvent, the actual chlorine content of the polymers was probably even closer to the theoretical value.) The chlorine content of the insoluble residue was much lower. Thus, the insoluble residue of samples obtained from the experiments illustrated by Table III contained typically only 46-49% Cl. 

Microwave laboratory ovens are currently quite popular. Where applicable, these greatly shorten drying cycles. For example, slurry samples that require 12 to 16 hours for drying in a conventional oven are reported to be dried within 5 to 6 minutes in a microwave oven. The time needed to dry silver chloride, calcium oxalate, and barium sulfate precipitates for gravimetric analysis is also shortened significantly. ... 

Differential scanning calorimetry and thermal gravimetric analysis have been used by several authors (27,53) to show that plasma-derived polymers have no phase transitions until decomposition occurs. The remarkable thermal stability of these materials is evidenced by data which show that 80 wt.% of a film prepared from methyl chloride remains at 800 C and that 40 wt.% of a styrene derived film remains at 700°C. 

Distilled water must be used in the gravimetric analysis of chlorides. Why ... 

A successful gravimetric analysis consists of a number of important operations designed to obtain a pure and filterable precipitate suitable for weighing. You may wish to precipitate silver chloride from a solution of chloride by adding silver nitrate. There is more to the procedure than simply pouring in silver nitrate solution and then filtering. 

We take advantage of the common ion effect to decrease the solubility of a precipitate in gravimetric analysis. For example, sulfate ion is determined by precipitating BaS04 with added barium chloride solution. Figure 10.3 illustrates the effect of excess barium ion on the solubility of BaS04. 

Worked example 6.5 illustrates the use of the common-ion effect in gravimetric analysis AgCl is always precipitated from a solution containing a slight excess of a common ion, CP or Ag , in the determination of silver or chloride respectively. 

The precipitation of chloride and, if present, dissolved bromide and iodide as the total of dissolved halide ions by silver salts as low-solubility silver halides is also not only used for concentrating traces of bromide and iodide for example, but also for gravimetric analysis, as a method of calibration. Bromide and iodide should then be determined separately (Section 3.2) and subtracted from the total of the precipitated halides. Reliable results are then obtained even at high concentrations. 

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