Potassium chromate, as indicator

Anion exchange resin. Proceed as in the previous experiment using 1.0 g, accurately weighed, of the air-dried strongly basic anion exchanger (e.g. Duolite A113, chloride form). Fill the 250 mL separatory funnel with ca 0.25M sodium nitrate solution, and allow this solution to drop into the column at the rate of about 2 mL per minute. Collect the effluent in a 500 mL conical flask, and titrate with standard 0.1M silver nitrate using potassium chromate as indicator. 

Discussion. Very pure silver can be obtained commercially, and a standard solution can be prepared by dissolving a known weight (say, 10.787 g) in nitric acid in a conical flask having a funnel in the neck to prevent mechanical loss, and making up to a known volume (say, 1 L for a 0.1 M solution). The presence of acid must, however, be avoided in determinations with potassium chromate as indicator or in determinations employing adsorption indicators. It is therefore preferable to employ a neutral solution prepared by dissolving silver nitrate (relative molecular mass, 169.87) in water. 

Potassium chloride (nitrate) bridge 583, 582 Potassium chromate as indicator, 343, 349 Potassium cyanoferrate(II) D. of, (ti) 384 Potassium cyanoferrate(III) D. of, (ti) 399 Potassium cyanonickelate(II) prepn., 328 Potassium dichromate solution analyses involving, 375 oxidising properties of, 375 internal indicators for, 377 preparation of, 0.02M, 375 redox indicators for, 377 standardisation of, by iron, (cm) 546, (ti) 376... 

Elemental composition (anhydrous MgCE) Mg 25.54%, Cl 74.46%. Aqueous solution of the salt may he analyzed for Mg hy AA or ICP method (See Magnesium). The chloride ion can he identified hy ion chromatography or measured by titration with a standard solution of silver nitrate using potassium chromate as indicator. 

Elemental composition P 37.78%, H 3.69%, 0 58.54%. The acid in solid form may be identified by its physical properties. Aqueous solution may be heated and phosphorus acid is converted to phosphoric acid which is measured for orthophosphate ion by ion chromatography or colorimetry (see Phosphoric Acid). A cold aqueous solution may be analyzed for phosphite ion by ion chromatography, following appropriate dilution. Strength of the acid in an aqueous solution may be measured by acid-base titration using a standard solution of alkali. Also, titration against a standard solution of silver nitrate using potassium chromate as indicator may serve as an additional confirmatory test. 

The chlorides may also be determined vohrmetrically by the following method,1 which effects the removal of the phosphates from the beer 50 c.c. of the beer are evaporated with 0-5 gram of barium carbonate and subsequently ignited to a black ash. The latter is extracted with hot water and filtered, the filtrate being then titrated with standard silver nitrate solution in presence of potassium chromate as indicator. 

The chloropicrin, on coming into contact with the alcoholic solution of sodium peroxide, decomposes, forming sodium chloride, which may be determined volumetrically with a N/ioo solution of silver nitrate (using potassium chromate as indicator), after neutralising the alcoholic solution with sulphuric acid (to the phenolphthalein end-point). 

Volumetric determination with visual indication (potassium chromate as indicator)... 

These three phases were gently stirred without mixing at 25 i 1 °C using a magnetic stirrer. At specified time intervals, the concentrations of metal picrate in both aqueous phases were determined by UV spectroscopy. It was confirmed by the silver nitrate titration method using 5% potassium chromate as indicator that no chloride ion was transported from, aqueous phase I to aqueous phase II. 

Salt may be determined in 50 c.c. of the filtered aqueous extract of the incinerated soap, by exactly neutralising with normal acid and titrating with N/10 silver nitrate solution, using a neutral solution of potassium chromate as indicator. The final reaction is more distinctly observed if a little bicarbonate of soda is added to the solution. 

The conditions must be strictly adhered to and low laboratory temperatures must be avoided also the reaction mixture must not be heated, otherwise the excess of alkali decomposes the chloroform formed and high results are obtained. This was confirmed by Harrington, Boyd and Cherry who showed that some hydrolysis of the chloroform occurred at room temperature in the excess of alkali present. If, after neutralisation of the excess alkali, the chloride formed is titrated with OTN silver nitrate using potassium chromate as indicator, a correction for this hydrolysis is possible. Since 3 mols. of sodium chloride produced are equivalent to 4 mols. of sodium hydroxide required for the chloroform hydrolysis, 2/15 of the silver nitrate titration must be deducted from the N sodium hydroxide absorbed in the original hydrolysis. 

Titration of chloride ion by silver nitrate using potassium chromate as an indicator... 

Addition of silver nitrate to a solution of a chloride in dilute nitric acid gives a white precipitate of silver chloride, AgCl, soluble in ammonia solution. This test may be used for gravimetric or volumetric estimation of chloride the silver chloride can be filtered off, dried and weighed, or the chloride titrated with standard silver nitrate using potassium chromate(VI) or fluorescein as indicator. 

Silver nitrate is used volumetrically to estimate chloride, bromide, cyanide and thiocyanate ions. Potassium chromate or fluorescein is used as an indicator. 

Chloride. The chloride concentration is determined by titration with silver nitrate solution. This causes the chloride to be removed from the solution as AgCl, a white precipitate. The endpoint of the titration is detected using a potassium chromate indicator. The excess Ag present after all Cl" has been removed from solution reacts with the chromate to form Ag CrO, an orange-red precipitate. 

Chlorine at the percentage level at which it occurs in sea water is usually determined by classical procedures using standard silver nitrate as the titrant and potassium chromate indicator, or alternatively by the mercuric thiocyanate procedure using dithizone as indicator. As large dilutions of the original sample are involved in these analyses, it is essential to use grade A glassware and take all other suitable precautions, such as temperature control. 

Procedure Weigh accurately about 0.25 g of potassium chloride in a conical flask and dissolve it in 50 ml of DW and titrate with 0.1 N silver nitrate solution, using 2-3 drops of potassium chromate solution as indicator till precipitation of red chromate is indicated. Each ml of 0.1 N silver nitrate solution is equivalent to 0.007455 g of KC1. 

Potassium chromate may be used as an indicator producing a red colour with excess Ag ion. More widely applicable is the method of back titration. Excess AgNOj is added to the sample containing chloride or bromide ions. The excess AgNOj is then titrated with ammonium thiocyanate and ammonium ferrous sulphate is used as an indicator of excess SCN. ... 

Chlorides, bromides, and iodides can be quantitatively determined by treatment with silver nitrate, and, with suitable precautions, the precipitated halide is washed, dried, and weighed. Chlorides in neutral soln. can be determined by F. Mohr s volumetric process 27 by titration with a standard soln. of silver nitrate with a little potassium chromate or sodium phosphate as indicator. When all the chloride has reacted with the silver nitrate, any further addition of this salt gives a yellow coloration with the phosphate, and a red coloration with the chromate. In J. Volhard s volumetric process, the chloride is treated with an excess of an acidified soln. of silver nitrate of known concentration. The excess of silver nitrate is filtered from the precipitated chloride, and titrated with a standard soln. of ammonium thiocyanate, NH4CN8—a little ferric alum is used as indicator. When the silver nitrate is all converted into thiocyanate AgN03-fNH4CNS=AgCNS +NH4NOS, the blood-red coloration of ferric thiocyanate appears. 

Quantitative Determination. Dissolve I gin. of potassium chromate in water and dilute to 100 re. Introduce 10 cc. of this solution into a glass-stoppered llask of about 400 cc. capacity, add 2 gin. of potassium iodide, 5 cc. of 10 per cent, sulphuric acid, and 350 cc. of thoroughly boiled water, ntrale the liberated iodine with deeinoriual sodium thiosulphate, using starch solution as the indicator. 

Ag+ preferentially reacts with the analyte to form a soluble salt or complex. During this addition, Ag+ reacts with the analyte only, and not the indicator. But when all the analyte is completely consumed by Ag+ and no more of it is left in the solution, addition of an excess drop of silver nitrate titrant produces an instant change in color because of its reaction with the silver-sensitive indicator. Some of the indicators used in the argentometric titrations are potassium chromate or dichlorofluorescein in chloride analysis and p -dime thy la m i nobe nzalrho da n i nc in cyanide analysis. Silver nitrate reacts with potassium chromate to form red silver chromate at the end point. This is an example of precipitation indicator, where the first excess of silver ion combines with the indicator chromate ion to form a bright red solid. This is also known as Mohr method. 

Exposure to chromium(VI) can result in DNA-protein complexes, the identification of which may be useful as biomarkers of exposure to chromates (Costa 1991). Gel electrophoresis and immunochemical techniques were used to identify actin as the protein in a DNA-protein complex induced by potassium chromate in cultured Chinese hamster ovary cells. While the DNA-protein complexes induced by formaldehyde and ultraviolet light were different from those induced by chromate, actin was also identified as the protein in the complex induced by cis-platinum, indicating that the DNA-actin complex is not specific for chromium. However, an experiment in a group of four volunteers did not demonstrate an increase in DNA-protein crosslinks in leukocytes over a 240 minute period following the ingestion of 5 mg chromium(VI) as potassium dichromate in a 10 mg chromium/L solution or the same amount added to 300 mL of orange juice (presumably reducing chromium(VI) to chromium(III)) and diluted to 500 mL with deionized water (Kuykendall et al. 1996). Chromium levels in red cells, plasma and urine were increased. In a separate experiment in this study, a threshold dose of 52 pg chromium(VI)/L was determined for crosslink formation in cultured lymphoma cells. 

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