Chloride ion with silver

The following procedures were reported for the assay of Melphalan Tablets (a) hydrolysis with aqueous potassium hydroxide under reflux and potentiometric titration of the liberated chloride ions with silver nitrate in the presence of nitric acid. (Corrections for "ionisable chlorine" are made by titrating under the same conditions a sample that is not subjected to hydrolysis [25,46].) (b)... 

Fluorescein is a typical adsorption indicator that is useful for the titration of chloride ion with silver nitrate. In aqueous solution, fluorescein partially dissociates into hydronium ions and negatively charged fluoresceinate ions that are yellow-green. The fluoresceinate ion forms an intensely red silver salt. Whenever this dye is used as an indicator, however, its concentration is never large enough to precipitate as silver fluoresceinate. 

Precipitation. In the case of precipitation, the titrant forms an insoluble product with the analyte. An example is the titration of chloride ion with silver nitrate solution to form silver chloride precipitate. Again, indicators can be used to detect the end point, or the potential of the solution can be monitored electrically. 

The indicating electrode in precipitation titrations is used to follow the change in pM or pA, where M is the cation of the precipitate and A is the anion. In the titration of chloride ion with silver ion, for example, either Equation 13.3 or 13.10 will hold. In the former equation, the term log (1/uAg ) is equal to pAg and in the latter equation, the term log Oq- is equal to —pCl. Therefore, the potential of the silver electrode will vary in direct proportion to pAg or pCl, changing 2.30 RT/F V (ca. 59 mV) for each 10-fold change in or flci-- A plot of the potential versus volume of titrant will give a curve identical in shape to that in Figure 11.1. (Note that since aAg+<3a- = constant, Uci- is proportional to and pCl is proportional to — pAg, so the same shape curve results if we plot or measure either pCl or pAg.)... 

Consider the titration of chloride ion with silver nitrate solution. Except near the equivalence point where the solubility becomes appreciable compared to the unreacted chloride, the concentration of chloride in solution at any point in the titration is calculated from the initial moles less the moles reacted with AgNOs ... 

The solution after mixing will be hot from the heat of neutralization. Evaporate it on the steam bath to about 120 ml filter it further, while hot, from any sediment evaporate to about 80 ml, and cool the filtrate to room temperature finally cool in ice and filter out the crystals on a small Buchner funnel. Recrystallize from a minimum volume of hot water, again cooling in ice to get the crystals. Suck them as dry as possible and bottle them. Dissolve a small amount of the salt in water and test for neutrality with methyl red, and for chloride ion with silver nitrate. 

Alternative methods for salt determination include use of a chloride ion-selective electrode and a semi-quantitative indicating strip method based on the reaction of chloride ion with silver chromate to produce silver chloride. 

Qualitative. The classic method for the quaUtative determination of silver ia solution is precipitation as silver chloride with dilute nitric acid and chloride ion. The silver chloride can be differentiated from lead or mercurous chlorides, which also may precipitate, by the fact that lead chloride is soluble ia hot water but not ia ammonium hydroxide, whereas mercurous chloride turns black ia ammonium hydroxide. Silver chloride dissolves ia ammonium hydroxide because of the formation of soluble silver—ammonia complexes. A number of selective spot tests (24) iaclude reactions with /)-dimethy1amino-henz1idenerhodanine, ceric ammonium nitrate, or bromopyrogaHol red [16574-43-9]. Silver is detected by x-ray fluorescence and arc-emission spectrometry. Two sensitive arc-emission lines for silver occur at 328.1 and 338.3 nm. 

How could you determine the mole ratios in these compounds Most chloride compounds dissolve in water, but some do not. Reacting dissolved chloride ions with a cation that forms an insoluble chloride compound can be used to determine the amount of chloride ions present. One such cation is silver. Reacting a chloride-containing solution with sufficient silver nitrate (AgN03) solution will precipitate any dissolved chloride ions. A solution of KCI will react with a certain amount of AgN03. The same volume of BaCI2 solution of the same concentration will require twice as much AgN03 to precipitate all the Cl ions. 

The possibility of the oxidation of Cl and SCN ions were also examined. 10 ml of 500 ppm neutral FeCl3 solution was sonicated for 30 min, while the control sample was kept for the same duration in the atmospheric condition. These sonicated and controlled samples were treated with AgN03 to precipitate unaffected remaining amount of chloride ions as silver chloride. The amount of precipitable chloride was same in both sonicated as well as unsonicated solutions. Similarly, the reappearance of pink colour in the sonicated and decolourised solution of I e(SC )6]3 upon the addition of FeCl3 confirmed that the SCN- too did not oxidize during the decomposition and decolourisation of the complex but remained unaffected even after the complex had perished. 

The units are correct in the calculation of [Ag. It seems reasonable that a precipitate formed, since Kgp for silver chloride is very small compared with the concentration of chloride ions and silver ions. 

To test for chlorine in the presence of iodine and/or bromine, acidify 1-2 ml of the fusion solution with glacial acid, add a slight excess of lead dioxide (say, 0.5 g) and boil gently until all the iodine and bromine is liberated. Dilute, filter off excess lead dioxide and test for chloride ions with dilute nitric acid and silver nitrate solution. 

This expression shows that under equilibrium conditions the concentration of chromate ions in the solution is always much greater than that of the chloride ions. If therefore to a mixture of chloride and chromate ions, silver ions are added, these will combine with chloride ions, forming silver chloride precipitate until the concentration of chloride ions in the solution decreases to such an extent, that the ratio expressed in equation (iii) is achieved. From then onwards the two precipitates will be formed simultaneously. If a 01m solution of sodium chloride is titrated with silver nitrate in the presence of 0 002m potassium chromate, the concentration of chloride ions at which silver chromate starts to precipitate can be expressed from equation (iii) ... 

Figure 20-3. Potentiometric titration curve of chloride titrated with silver ion.

The silver chloride cathode reaction is given by Eq. (8) in reverse that is, silver chloride is reduced to form metallic silver and chloride ion. The silver chloride cathode shares many of the qualities of the silver anode, with some additional desirable traits No electrolyte is depleted by its reaction it is hydrophilic and therefore wetted by the reservoir electrolyte and the insoluble reaction product, metallic silver, is electrically conductive, eliminating problems of polarization or isolation of the redox species. Because of this combination of properties, the operating voltage of silver chloride decreases with use, and the utilization of a silver chloride cathode is nearly 100%. 

The methods developed in the previous section for deriving titration curves can be extended to mixtures that form precipitates of different solubilities. To illustrate, consider the titration of 50.00 mL of a solution that is 0.0500 M in iodide ion and 0.0800 M in chloride ion with 0.1000 M silver nitrate. The curve for the initial stages of this titration is identical to the curve shown for iodide in Figure 13-5 because silver chloride, with its much larger solubility product, does not begin to precipitate until well into the titration. 

Figure 21-9a shows a typical cell for measuring pH. The cell consists of a glass indicator electrode and a saturated calomel reference electrode immersed in the solution of unknown pH. The indicator electrode consists of a thin, pH-sensitive glass membrane sealed onto one end of a heavy-walled glass or plastic tube. A small volume of dilute hydrochloric acid saturated with silver chloride is contained in the tube. (The inner solution in some electrodes is a buffer containing chloride ion.) A silver wire in this solution forms a silver/silver chloride reference electrode, which is connected to one of the terminals of a potential-measuring device. The calomel electrode is connected to the other terminal. 

Figure 21-21 Titration of 2.433 mmol of chloride ion with 0.1000 M silver nitrate, (a) Titration curve, (b) First-derivative curve, (c) Second-derivative curve.

A reagent solution 0.011 M in iron(lll) is prepared by dissolving 0.6142 g of electrolytically pure iron wire in 75 ml of 6.0 M perchloric acid. The solution is heated below boiling until the volume is reduced to 25 ml, transferred to a 1-liter volumetric flask, and diluted to the mark with distilled water, giving a solution 0.01 M in iron(lll). Test for iron(ll) and for chloride ions with potassium ferricyanide and silver nitrate, respectively, should be negative. 

In a chemical equation, the numbers in front of the separate atoms, ions or molecules are known as coefficients they indicate exactly how many of the atoms, ions or molecules react with another type of atoms, ions or molecules in order for a complete reaction. As an example, let us look at the well-known reaction of calcium chloride solution with silver nitrate solution to form insoluble silver chloride ... 

A further displacement of practical utility is that of halogen in phosphonic and phos-phinic chlorides by carboxylate ions (with silver or thallium salts, for example) to give mixed anhydrides, e.g. 581 and 582. Such anhydride formation provides a system particularly reactive at the carbonyl group towards nucleophiles, and thus preliminary activation of the carboxyl group by the diphenylphosphinoyl group becomes useful in amide or peptide formation ... 

S04 see Conservative Elements). The analytical results reported by W. Dittmar in 1884 for waters collected during the British RMS Challenger Expedition (1872-1876) from the world s oceans were almost the same as today s values. The constancy of major chemical composition has led oceanographers to define salinity as a fundamental property together with temperature to calculate the density of sea water. It was routine for classic physical oceanographers to titrate sea water for chloride (plus bromide) ion with silver nitrate standard solution, until the mid 1960s when salinity could be determined more practically by measurement of conductivity. 

These are called precipitation reactions because they take place in water ( aqueous or aq ) solution and one compound is precipitated out of the solution (and can then be filtered, washed, recrystallised etc.). As with displacement reactions, some of the species present do not actually take any active part in the process (and so are called spectator ions). So in the first example, sodium chloride and silver nitrate are both soluble, so what is actually being mixed is a solution containing hydrated sodium ions and hyclrated chloride ions, with one containing hydrated silver ions and hydrated nitrate ions. The compound silver chloride has very low solubihty (the bonding between the ions is not readily broken down to allow hydration of the ions), so is precipitated from the solution ... 

Many different types of indicator electrodes can be used as endpoint indicators in potentiometric titrations. For example, an acid-base titration can be performed with a glass electrode as endpoint detector instead of using colored indicators, or chloride ions can be titrated with silver(I) using a chloride-ion- or silver-ion-selective electrode. 

---