Starch indicator

The Turing mechanism requires that the diffusion coefficients of the activator and inlribitor be sufficiently different but the diffusion coefficients of small molecules in solution differ very little. The chemical Turing patterns seen in the CIMA reaction used starch as an indicator for iodine. The starch indicator complexes with iodide which is the activator species in the reaction. As a result, the complexing reaction with the immobilized starch molecules must be accounted for in the mechanism and leads to the possibility of Turing pattern fonnation even if the diffusion coefficients of the activator and inlribitor species are the same 62. 

Hydrazine hydrate may be titrated with standard acid using methyl orange as indicator or, alternatively, against standard iodine solution with starch as indicator. In the latter case about 0-1 g., accurately weighed, of the hydrazine hydrate solution is diluted with about 100 ml. of water, 2-3 drops of starch indicator added, and immediately before titration 6 g. of sodium bicarbonate are introduced. Rapid titration with iodine gives a satisfactory end point. 

A 25.00-mL sample of a liquid bleach was diluted to 1000 mb in a volumetric flask. A 25-mL portion of the diluted sample was transferred by pipet into an Erlenmeyer flask and treated with excess KI, oxidizing the OCh to Ch, and producing The liberated was determined by titrating with 0.09892 M NaySyOy, requiting 8.96 mb to reach the starch indicator end point. Report the %w/v NaOCl in the sample of bleach. 

The purity of a sample of Na2S203 was determined by a coulometric redox titration using as a mediator, and as the titrant. A sample weighing 0.1342 g is transferred to a 100-mL volumetric flask and diluted to volume with distilled water. A 10.00-mL portion is transferred to an electrochemical cell along with 25 mL of 1 M KI, 75 mL of a pH 7.0 phosphate buffer, and several drops of a starch indicator solution. Electrolysis at a constant current of 36.45 mA required 221.8 s to reach the starch indicator end point. Determine the purity of the sample. 

Ofner Method. This method is for the determination of invert sugar in products with up to 10% invert in the presence of sucrose and is a copper-reduction method that uses Ofner s solution instead of Fehling s. The reduced cuprous oxide is treated with excess standardized iodine, which is black-titrated with thiosulfate using starch indicator. 

These titrations can be done manually using a starch indicator for end point detection or more accurately by amperometric methods. 

A simple test for ether peroxides is to add lOmL of the ether to a stoppered cylinder containing ImL of freshly prepared 10% solution of potassium iodide containing a drop of starch indicator. No colour should develop during one minute if free from peroxides. Alternatively, a 1% solution of ferrous ammonium sulfate, O.IM in sulfuric acid and O.OIM in potassium thiocyanate should not increase appreciably in red colour when shaken with two volumes of the ether. 

The dependence of reaction rates on pH and on the relative and absolute concentrations of reacting species, coupled with the possibility of autocatalysis and induction periods, has led to the discovery of some spectacular kinetic effects such as H. Landolt s chemical clock (1885) an acidified solution of Na2S03 is reacted with an excess of iodic acid solution in the presence of starch indicator — the induction period before the appearance of the deep-blue starch-iodine colour can be increased systematically from seconds to minutes by appropriate dilution of the solutions before mixing. With an excess of sulfite, free iodine may appear and then disappear as a single pulse due to the following sequence of reactions ... 

The net reaction is the disproportionation of H2O2 to H2O + 5O2 and the starch indicator oscillates between deep blue and colourless as the iodine concentration pulsates. 

A solid solution of starch in urea may also be employed. Reflux 1 g of soluble starch and 19 g of urea with xylene. At the boiling point of the organic solvent the urea melts with little decomposition, and the starch dissolves in the molten urea. Allow to cool, then remove the solid mass and powder it store the product in a stoppered bottle. A few milligrams of this solid added to an aqueous solution containing iodine then behaves like the usual starch indicator. 

Alternative procedure. The following method utilises a trace of copper sulphate as a catalyst to increase the speed of the reaction in consequence, a weaker acid (acetic acid) may be employed and the extent of atmospheric oxidation of hydriodic acid reduced. Place 25.0 mL of 0.017M potassium dichromate in a 250 mL conical flask, add 5.0 mL of glacial acetic acid, 5 mL of 0.001M copper sulphate, and wash the sides of the flask with distilled water. Add 30 mL of 10 per cent potassium iodide solution, and titrate the iodine as liberated with the approximately 0.1M thiosulphate solution, introducing a little starch indicator towards the end. The titration may be completed in 3-4 minutes after the addition of the potassium iodide solution. Subtract 0.05 mL to allow for the iodine liberated by the copper sulphate catalyst. 

Procedure. Pipette 25.0 mL standard (0.05M) iodine solution into a 500 mL conical flask and add 5 mL 2M hydrochloric acid and 150 mL distilled water. Weigh accurately sufficient solid sulphite to react with about 20 mL 0.05M iodine solution and add this to the contents of the flask swirl the liquid until all the solid has dissolved and then titrate the excess iodine with standard (0.1M) sodium thiosulphate using starch indicator. If the sulphite is in solution, then a volume of this equivalent to about 20 mL of 0.05M iodine should be pipetted into the contents of the flask in place of the weighed amount of solid. 

The concentration of the potassium bromate can be checked by the following method pipette 25 mL of the solution into a 250 mL conical flask, add 2.5 g of potassium iodide and 5 mL of 3M sulphuric acid. Titrate the liberated iodine with standard 0.1M sodium thiosulphate (Section 10.114) until the solution is faintly yellow- Add 5 mL of starch indicator solution and continue the titration until the blue colour disappears. 

The polyester is stable in storage at RT. The thermal stability at 65.5° using a 1.3g sample and Kl-Starch indicator paper is failure after 100 mins (Ref NC, 10 min, no color) at 134,5 using a 2.5g sample and Methyl violet paper, failure is shown after SO mins (Ref NC, 30 mins, no color)... 

The polymer has an impact sensy of 40cm at the 50% point using a BM machine with a 2kg wt (RDX, 28cm), a thermal stability of 13 mins using a 1.3g sample with Kl-Starch indicator paper (Ref NC, 10 mins, no color), also, a rel vise of 1.50 centipoises at 25° using a 1% acet soln Ref PJ. Blatz et al, Research In Nitropoly-mers And Their Application To Solid Smokeless Propellants , Report No 907, Aerojet-General Corp, Azusa, Calif ONR Contract N7 onr-462, Task Order I and Contract NO as 54-399-C (15 Dec 1954), 16 17... 

Starch Indicator. Five grams of soluble starch were dissolved in 1 liter of distilled water. A few drops of toluene were placed on top of the solution as a preservative. 

Aspirate through ammoniacal cadmium chloride strip sulfur dioxide by aeration dissolve cadmium sulfide precipitate in concentrated HC1 titrate with iodine using a starch indicator. Iodometric titration 0.7 qg/L NR EPA 1978... 

Hi) End-point is almost colourless, hence starch indicator can be skipped totally, and... 

SO2 content of the gas was determined by sparging into a 125 ml gas washing bottle containing a known amount of I2 in acetate buffer at pH A-5.5 with a starch indicator. N2 flow was measured by a wet test meter. 

In the iodate detection system (ASTM D1552), the sample is burned in a stream of oxygen at a sufficiently high temperature to convert about 97% by weight of the sulfur to sulfur dioxide. The combustion products are passed into an absorber containing an acidic solution of potassium iodide and starch indicator. A faint blue color is developed in the absorber solution by the addition of standard potassium iodate solution. As combustion proceeds, bleaching the blue color, more iodate is added. The sulfur content of the sample is calculated from the amount of standard iodate consumed during the combustion. 

The compound is digested with nitric acid and the solution is analyzed for antimony by AA or ICP spectrophotometry (see Antimony). To determine the chlorine content a measured amount of substance is heated at 300°C and the liberated CI2 is passed into an acidic solution of KI and analyzed by iodomet-ric titration using a standard solution of sodium thiosulfate or phenyl arsine oxide and starch indicator. 

Chlorine gas may be identified readdy by its distinctive color and odor. Its odor is perceptible at 3 ppm concentration in air. Chlorine may be measured in water at low ppm by various titrimetry or colorimetric techniques (APHA, AWWA and WEF. 1999. Standard Methods for the Examination of Water and Wastewater, 20th ed. Washington DC American Pubhc Health Association). In iodometric titrations aqueous samples are acidified with acetic acid followed by addition of potassium iodide. Dissolved chlorine liberates iodine which is titrated with a standard solution of sodium thiosulfate using starch indicator. At the endpoint of titration, the blue color of the starch solution disappears. Alternatively, a standardized solution of a reducing agent, such as thiosulfate or phenylarsine oxide, is added in excess to chlorinated water and the unreacted reductant is then back titrated against a standard solution of iodine or potassium iodate. In amperometric titration, which has a lower detection limit, the free chlorine is titrated against phenyl arsine oxide at a pH between 6.5 and 7.5. 

Hydrazine reduces iodine to hydrogen iodide. Thus, an excess of standard solution of iodine is added to a measured volume of aqueous hydrazine solution and the excess iodine is back titrated at pH 7.0 to 7.2 (buffered by sodium bicarbonate) against a standard solution of sodium thiosulfate using starch indicator. 

Iodic acid can be analyzed by iodometric titration. Its acidic aqueous solution reacts with potassium iodide to liberate iodine (as shown above). Liberated iodine may be titrated against a standard solution of sodium thiosulfate using starch indicator. At the end point, the blue color of the solution... 

Iodine in aqueous solution may be measured quantitatively by acidifying the solution, diluting it, and titrating against a standard solution of sodium thiosulfate, sodium arsenite or phenyl arsine oxide using starch indicator. The blue color of the starch decolorizes at the end point. The indicator must be added towards the end of titration when the color of the solution turns pale yellow. Prior to titration, iodine in the dilute acidic solution is oxidized to iodate by adding bromine water or potassium permanganate solution. Excess potassium iodide is then added. The liberated iodine is then titrated as above. 

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