PH indicator papers

The solvents were evaporated in vacuo, and the residue was taken up in 80 ml of 3M hydrochloric acid. After addition of 220 ml of water, the insoluble material was filtered off, washed with 100 ml of water and then dried. The insoluble material weighed 9.5 g and was mainly unreacted bromo compound. The filtrate was reacted with 50 ml of 7 M NaOH, extracted three times with methylene chloride (50 m -t 2 x 25 ml portions), dried over potassium carbonate, and then evaporated. The yield of residue was 26.8 g which corresponds to 71.4% of the theoretical yield. This residue was a colorless solidifying oil and was dissolved in 200 ml chloroform. Hydrogen chloride was bubbled in until a sample of the solution tested acidic to wet pH indicator paper. A precipitate was obtained and recovered by filtration. The precipitate was washed with chloroform and dried. The melting point was determined to be from 246 Cto247.5°C. 

Weigh 25-100 g (ota) of the sample having a water content of xg/lOOg into a glass jar. Adjust the pH to ca 7 (using pH indicator paper) by adding small portions... 

The filtrate was acidified with HCl 12 m (approximately 20 mL) to pH 2.0, monitored with Whatman pH indicator paper. The resulting precipitate was collected on filter paper and dried under vacuum to afford 4-fluorobenzyl hydantoin (8.4 g, 87 %). 

In a 2-1. three-necked flask equipped with a stirrer and thermometer are placed 336 g. (2.62 moles) of 3,4-dihydro-2-methoxy-4-methyl-2H-pyran,2 630 ml. of water, and 24 ml. of concentrated hydrochloric acid (sp. gr. 1.19). The mixture is stirred for 2 hours, during which the temperature may reach 50° but should not be permitted to rise higher. Solid sodium bicarbonate is then added until the solution is neutral to pH indicator paper Note 1). The entire reaction mixture weighing about 1 kg. together with 39 g. of Raney nickel is introduced into a 3-1. 

The checkers found that pH indicator paper (sensitivity +/-1 pH unit) can also be used to monitor the acidity of the solution to pH 3. 

Identification of Amatol, a) Place about 0.05 g of previously pulverized unknown material in a 5-cc beaker, add 2 to 3 cc of distilled water, stir for 5 mins and observe the color of aliquot. It is colorless in case of amatols b) Test the aliquot with a strip of Universal pH indicator paper-.there shall be no change in color c) Add a drop of Ness-ler s reagent — brown ppt in case of amatol. 

For testing, place ca 0.05g of the unknown sample in a 5-ml beaker, add 2-3ml of distd w, stir for 5 mins and observe the color. Dip one end of a strip of universal pH indicator paper, and note any change in color. Add a... 

Optical sensors for ions use indicators, which exist in two different colors, depending on whether the analyte is bound to them. The use of colored indicators is one of the oldest principles of analytical chemistry, used extensively both in direct analytical spectroscopy and in so-called visual titrations. In their sensing application, the indicator is confined to the surface of the optical sensor or immobilized in the selective layer. In that sense, the oldest and most widespread optical sensor is a pH indicator paper, the litmus paper, which is commonly used for the rapid and convenient semiquantitative estimate of pH of solutions or for endpoint detection in acidobasic titrations. Its hi-tech counterpart is a pH optrode (the name of which is intentionally reminiscent of the pH electrode), which essentially does the same thing (Wolfbeis, 2004). The operation principles and limitations of ion optical sensors are common for all ions. 

The pH of an aqueous sample may be measured by the electrometric or colorimetric method. The latter, which involves the use of pH indicator papers,... 

These can be considered as a variant on optical sensors where the detection device is the human eye. Although it is unlikely that they would give a quantitative measurement of anion concentration, they can be used as simple tests to determine whether a particular anion is present above a certain concentration. If the dyes could be adsorbed onto paper and still remain active, an anion equivalent of pH indicator paper would be created. 

The pH of a solution can be measured conveniently by special instruments called pH meters. All that must be done is to insert the electrodes of the pH meter into the solution to be measured and read the pH from a scale. pH of a solution can also be obtained, although less precisely, by using a pH indicator paper. The paper is impregnated with organic compounds that change their color at different pH values. The color shown by the paper is then compared with a color chart provided by the manufacturer. 

Test the pH of each of the aqueous solutions. Do the test by first dipping a clean glass rod into the solutions and then transferring a drop of liquid to pH paper. Use a broad pH indicator paper (e.g., pH range 1-12) and read the value of the pH by comparing the color to the chart on the dispenser. Record the results on the Report Sheet (2). 

If a pH meter is not available, perform the titration as above, but use pH indicator papers. After the addition of each increment and stirring, withdraw a drop of the solution with a Pasteur pipet. Touch the end of the pipet to a dry piece of the pH indicator paper. Compare the color of the indicator paper with the color on the charts supplied. Read the corresponding pH from the chart and record it on your Report Sheet. 

To measure the pH of each urine sample, use pH indicator paper such as pHydrion test paper within the pH range of 3.0 to 9.0. 

Solution A Pipet 2.0 mL of Standard Lead Solution (20 pig of Pb) into a 50-mL color-comparison tube, and add water to make 25 mL. Adjust the pH to between 3.0 and 4.0 (using short-range pH indicator paper) by adding 1 N acetic acid or 6 N ammonia, dilute to 40 mL with water, and mix. 

Dimathyl-3-hydroxy-6-heptenoic acid. In a 500-mL flask, the crude ester prepared in Part A (37.00 g, 0.199 mol) is dissolved in a 2 N solution of potassium hydroxide (KOH) in methanol (130 mL, 0.260 mol). The solution is stirred at 25°C and disappearance of the starting material is monitored by GLC (Note 9). After 5 hr saponification is complete and the methanol is evaporated at reduced pressure (Note 11). The residue is taken up with water (500 mL), extracted with diethyl ether (3 x 100 mL), and the organic phase is discarded. The aqueous phase is acidified (pH 2.5 on universal pH indicator paper) with - 6 N hydrochloric acid (about 60 mL) and extracted with diethyl ether (5 x 100 mL). These latter ethereal extracts are washed with water (2 x 30 mL) and then with saturated sodium chloride (2 x 30 mL). The organic phase is dried over sodium sulfate, and filtered. Evaporation at reduced pressure affords crude 3,6-dimethyl-3-hydroxy-6-heptenoic acid as a viscous yellow oil that can be used in... 

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