Chlorine titration

Whereas the composition of dissolved main solid compounds in seawater is rather constant all over the oceans, the freshwater in the Baltic Sea outbalanced by river discharge is dominated by calcium bicarbonate. For this reason, significant anomalies are observed in Baltic waters from the standard composition of seawater (Nehring and Rohde, 1966), in particular in the brackish surface water, with amount increasing toward the eastern and northern margins of the Baltic Sea. Directly measured densities of Baltic water compared with density determined from the seawater equation of state with Baltic water salinity measured by chlorinity titration resulted in a deviation of up to 0.123 kg/m (Millero and Kremling, 1976). This may result in uncertainties in estimating the thermodynamic properties of Baltic water, for example, the vertical stability. 

To determine salinity from bottle samples, bench salinometers have now replaced the chlorinity titration method almost completely, initially for practical reasons. Subsequently, as the 1978 Practical Salinity Scale has been adopted, consistent application of this scale requires the use of salinometers. 

In case of small bound active chlorine content B—A < 5 cm ), volume A correctly reflects the free chlorine. In the other case, the free active chlorine titration must be repeated with thioacetamide addition. Then 5 cm DPD reagent solution and 10 cm buffer solution are mixed together in a titration flask, and 100 cm sample solution is added to them. Immediately after, a certain volume of the thioacetamide solution is added to the mixture. The volume needed to eliminate the interference of chloramines depends on the value of B-A, as shown in Table 6.2. 

For available chlorine titrate 25 ml as above, but acidify with a minimum excess of acid. (When fresh this preparation should contain about 0-4 per cent available chlorine, but it quickly loses strength.) Neutralise the titrated liquid to methyl orange, add glycerol or mannitol and titrate the boric acid to phenolphthalein with 0 5N sodium hydroxide (see p. 133). 

Available Chlorine Titrations Liquid-Solid pH Measurements Acids and Bases General Formulae... 

In what way does a solution of hydrogen peroxide react with (a) chlorine water, (b) potassium permanganate solution, (c) potassium dichromate solution, (d) hydrogen sulphide 50 cm of an aqueous solution of hydrogen peroxide were treated with an excess of potassium iodide and dilute sulphuric acid the liberated iodine was titrated with 0.1 M sodium thiosulphate solution and 20.0 cm were required. Calculate the concentration of the hydrogen peroxide solution in g 1" ... 

Alternatively, a known weight of the pyrolusite may be heated with concentrated hydrochloric acid and the chlorine evolved passed into potassium iodide solution. The iodine liberated is titrated with sodium thiosulphate ... 

Transfer 25 ml. of this dilute solution by means of a pipette to a conical flask, and add similarly 50 ml. of Ml 10 iodine solution. Now-add 10% sodium hydroxide solution until the liquid becomes pale yeilow in colour, and allow the solution to stand, with occasional shaking, at room temperature for at least 10 minutes. Then acidify with dilute hydrochloric acid (free from chlorine) in order to liberate the remaining iodine. Titrate the latter w ith Mho sodium thiosulphate solution, using starch as an indicator in the usual way. 

Control experiment. This is not necessary if the sodium peroxide is known to be chlorine-free. If there is any doubt on this point, the whole operation should be repeated precisely as before, but omitting the organic halogen compound. A small thiocyanate titration value may be found, and this should be deducted from all determinations in which the above quantity of the particular batch of sodium peroxide is used. 

Wijs solution (for iodine number) dissolve 13 g resublimed iodine in 1 liter of glacial acetic acid (99.5%), and pass in washed and dried (over or through H2SO4) chlorine gas until the original thio titration of the solution is not quite doubled. There should be only a slight excess of iodine and no excess of chlorine. Preserve the solution in amber colored bottles sealed with paraffin. Do not use the solution after it has been prepared for more than 30 days. 

This is an indirect method of analysis because the chlorine-containing species do not react with the titrant. Instead the total chlorine residual oxidizes l to l3 , and the amount of 13 is determined by the redox titration with Na282 03. 

One of the most important applications of redox titrimetry is in evaluating the chlorination of public water supplies. In Method 9.3 an approach for determining the total chlorine residual was described in which the oxidizing power of chlorine is used to oxidize R to 13 . The amount of 13 formed is determined by a back titration with 8203 . 

Chlorine and bromine add vigorously, giving, with proper control, high yields of 1,2-dihaloethyl ethers (224). In the presence of an alcohol, halogens add as hypohaUtes, which give 2-haloacetals (225,226). With methanol and iodine this is used as a method of quantitative analysis, titrating unconsumed iodine with standard thiosulfate solution (227). 

Industrial Hquid chlorine is routinely analy2ed for moisture, chlorine, other gaseous components, NCl, and mercury foUowing estabHshed procedures (10,79). Moisture and residue content in Hquid chlorine is determined by evaporation at 20°C foUowed by gravimetric measurement of the residue. Eree chlorine levels are estimated quantitatively by thiosulfate titration of iodine Hberated from addition of excess acidified potassium iodide to the gas mixture. 

The chlorinity. Cl (%e), is determined by the titration of seawater with AgNO. It was defined as the chlorine equivalent of the total hahde concentration ia g kg seawater it is now defined as the mass ia grams of Ag necessary to precipitate the halogens (Cl and Br ) ia 328.5233 g of seawater. It has been adequately demonstrated that the relative composition of the major (greater than 1 m kg seawater) components of seawater is nearly constant. By measuriag one constituent of seawater, the composition of other components can be characterized. The constituent normally selected is the chlorinity. Cl... 

Sodium bicarbonate is generally added to increase alkalinity and muriatic acid (HCl) or sodium bisulfate (NaHSO ) to reduce it. In general, with acidic sanitizers such as chlorine gas or trichloroisocyanuric acid, ideal total alkalinity should be in the 100—120 ppm range, whereas, with alkaline products such as calcium, lithium, or sodium hypochlorite, a lower ideal total alkalinity of 80—100 ppm is recommended (14). Alkalinity is deterrnined by titration with standard sulfuric acid using a mixed bromcresol green—methyl red indicator after dechlorination of the sample with thiosulfate. Dechlorination with thiosulfate causes higher readings due to formation of hydroxyl ion (32) ... 

The total concentration or amount of chlorine-based oxidants is often expressed as available chorine or less frequendy as active chlorine. Available chlorine is the equivalent concentration or amount of Cl needed to make the oxidant according to equations 1—4. Active chlorine is the equivalent concentration or amount of Cl atoms that can accept two electrons. This is a convention, not a description of the reaction mechanism of the oxidant. Because Cl only accepts two electrons as does HOCl and monochloramines, it only has one active Cl atom according to the definition. Thus the active chlorine is always one-half of the available chlorine. The available chlorine is usually measured by iodomettic titration (7,8). The weight of available chlorine can also be calculated by equation 5. 

In solutions, the concentration of available chlorine in the form of hypochlorite or hypochlorous acid is called free-available chlorine. The available chlorine in the form of undissociated A/-chloro compounds is called combined-available chlorine. Several analytical methods can be used to distinguish between free- and combined-available chlorine (8). Bleaches that do not form hypochlorite in solution like chlorine dioxide and nonchlorine bleaches can be characterized by thek equivalent available chlorine content. This can be calculated from equation 5 by substituting the number of electrons accepted divided by two for the number of active chlorine atoms. It can also be measured by iodomettic titration. 

Ana.lysls. The available chlorine (av CI2) in hypochlorite solutions or soHds is deterrnined by reaction with aqueous KI, followed by acidification with either acetic or sulfutic acid and titration of the Hberated iodine with standard thiosulfate. The av CI2 in a hypochlorite is a measure of the oxidi2ing capacity expressed in terms of elemental chlorine one hypochlorite ion is equivalent to one CI2 molecule. Thus pure Ca(OCl)2 has an av CI2 of 2 x mol wt... 

The side-chain chlorine contents of benzyl chloride, benzal chloride, and benzotrichlorides are determined by hydrolysis with methanolic sodium hydroxide followed by titration with silver nitrate. Total chlorine determination, including ring chlorine, is made by standard combustion methods (55). Several procedures for the gas chromatographic analysis of chlorotoluene mixtures have been described (56,57). Proton and nuclear magnetic resonance shifts, characteristic iafrared absorption bands, and principal mass spectral peaks have been summarized including sources of reference spectra (58). Procedures for measuring trace benzyl chloride ia air (59) and ia water (60) have been described. 

Other Elements. To determine chlorine, the sample is mixed with Eschka s mixture and burned to convert the chlorine to chloride or decomposed in an oxygen bomb (18). Chloride is determined by titration (D2361) or using a chloride selective electrode (D4208) (18) (see... 

This reaction is the basis for the use of thiosulfates as antichlorine in the bleaching industry where they are used to destroy any excess of CI2 in the fibres. Bromine, being intermediate between iodine and chlorine, can cause 8203 to act either as a 1-electron or an 8-electron reducer according to conditions. For example, in an amusing and instmctive experiment, if concentrated aqueous solutions of 8203 and Br2 are titrated, and the titration is then repeated after having diluted both the 8203 and Br2 solutions 100-fold, then the titre will be found to have increased by a factor of exactly 8. 

The most characteristic property of the oxaziranes is tlieir strong oxidizing character which is approximately equal to that of hydrogen peroxide. Oxaziranes react with hydrochloric acid the chlorine thus liberated is, however, used up in secondary reactions. " Two equivalents of iodine are formed from acid iodide solutions according to Eq. Titration of the free iodine allows a simple estimation of... 

Chlorinity When a sample of sea water is titrated with silver nitrate, bromides and iodides, as well as chlorides are precipitated. In calculating the chlorinity (Cl), the entire halogen content is taken as chloride, and chlorinity is defined as the weight in grams of silver required for precipitation of total halogen content per kilogram of sea water, multiplied by 0-328 533. (Chlorinity is always expressed as parts per thousand, using the symbol %o.)... 

The presence of free bromine, and consequently the end-point, can be detected by its yellow colour, but it is better to use indicators such as methyl orange, methyl red, naphthalene black 12B, xylidine ponceau, and fuchsine. These indicators have their usual colour in acid solution, but are destroyed by the first excess of bromine. With all irreversible oxidation indicators the destruction of the indicator is often premature to a slight extent a little additional indicator is usually required near the end point. The quantity of bromate solution consumed by the indicator is exceedingly small, and the blank can be neglected for 0.02M solutions. Direct titrations with bromate solution in the presence of irreversible dyestuff indicators are usually made in hydrochloric acid solution, the concentration of which should be at least 1.5-2M. At the end of the titration some chlorine may appear by virtue of the reaction ... 

The chlorine content can be determined by either chlorine elemental analysis or a potentiometric titration using a chloride-ion electrode. For titration, about 0.2 g. of polymer is heated in 3 ml. of pyridine at 100° for 2 hours. This suspension is then transferred to a 50-mi. beaker containing 30 ml. of aqueous 50% acetic acid and 5 ini. of concentrated nitric acid, and the resulting mixture is titrated against aqueous 0.1 N silver nitrate. 

Then, in fast consecutive steps, chlorine dioxide is reduced to chloride. The induced reduction of chlorate is quantitative within a few minutes. At the beginning of the titration not only the special smell but also the faint-yellowish colour of chlorine dioxide can be observed after the complete disappearance of the cerium(IV) reagent. 

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