Universal pH indicator papers

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... 

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... 

Wet one end of a strip of universal pH indicator paper and note any change in color. 

We can determine an approximate value of the pH of an aqueous solution very quickly with a strip of universal indicator paper, which turns different colors at different pH values. More precise measurements are made with a pH meter (Fig. 10.11). This instrument consists of a voltmeter connected to two electrodes that dip into the solution. The difference in electrical potential between the electrodes is proportional to the hydronium ion activity (as will be explained in Section 12.10) so, once the scale on the meter has been calibrated, the pH can be read directly. 

Figure 17-3 shows the range of pH and hydronium ion concentrations. The measurement of pH is a routine operation in most laboratories. Litmus paper, which turns red when dipped in acidic solution and blue when dipped in basic solution, gives a quick, qualitative indication of acidity. As Figure 17-4 shows, approximate measures of pH can be done using pH paper. Universal pH paper displays a range of colors in response to different pH values and is accurate to about 0.5 pH unit. For quantitative pH determinations, scientists use pH meters. 

Put a piece of indicator paper (a universal indicator) on a watch glass and wet it with a sodium carbonate solution. Note the change in the indicator colour, compare it with a reference, and determine the pH of the sodium carbonate solution. Perform similar experiments with aluminium and sodium chlorides. Use the pH values obtained to calculate the hydrogen ion concentrations in the studied solutions. 

Universal indicator papers permit pH determinations over the total pH range from 0 to 14. The determination of the pH is made by comparing the color of the paper with a reference color scale. The accuracy is ca. 1 pH unit. 

Special indicator papers cover ranges from 2 to 5 pH units. The determination method is the same as with universal indicator papers. The accuracy is better 0.5 units is regularly attained under favorable conditions, 0.2-0.3 units is possible. 

Universal indicator paper strips for pH ranging from 0 to 14 and a reference color chart... 

Either carbon dioxide gas or Dry Ice may be used, and the saturation may be completed in 15-20 minutes by either method. The pH of the saturated solution is about 8-9 when tested with a universal indicator paper, such as Alkacid or Hydrion. 

Which do you think gave the more accurate pH the universal indicator paper or the pH meter Explain. 

Fill a column (about 1.5 cm in diameter) with Dowex 50W x 8 in the H+ form, about 8 cm deep. Wash the resin with 100 mL of deionized water and check the pH with universal indicator paper to ensure that the water coming out from the bottom of the column is neutral. 

Continue adding water to the top of the column as in step 4 until all of the pyrophosphoric acid solution has eluted. This may be checked by taking a small portion from a drip from the bottom of the column using a TLC spotter and checking the pH with universal indicator paper. If the effluent is still acidic the column should be washed further with deionized water until the pH of the effluent is neutral. 

The acidity, or alkalinity of a solution, is frequently assessed using universal indicator paper or solution, which is a mixture of a variety of indicators that go through a spectrum of colours as the acidity of a solution changes. In Table 5.5.2, pH values have been matched to ion concentration and the usual colour of universal indicator. 

Universal indicator paper turns different colors at different pH values. 

Universal indicator papers can also be used to determine pH. A drop of solution is placed on a piece of paper or a piece of the paper is dipped into a solution. The color of the paper is then compared with a color chart on the container to establish the pH of the solution. 

One important use of universal indicators is in commercial indicator papers, which are small strips of paper impregnated with solutions of universal indicators. A strip of the paper is dipped into the solution of interest, and the color of the indicator on the paper indicates the pH of the solution. The photographs on page 757 (solutions of universal indicators) and page 763 (an indicator paper) illustrate the use of universal indicators to estimate pH. We shall describe the use of indicators in titrations more fully in Sections 19-5 and 19-6. 

Measurements should be carried out with two different indicators, unless routine analyses are involved. When nothing at all is known of the acidity of the solution, the approximate pH must first be found in order to permit a choice of proper indicators. Of course only those indicators may be used which impart a distinct intermediate color to the unknown solution. An indicator is of no value if its color in the unknown solution is due to the pure acid or pure basic form. The preliminary examination for acidity may be performed with the use of various indicator papers such as congo, litmus, phenolphthalein, and turmeric papers, or by treating small portions of liquid (on a spot plate) with various indicators. If it happens, for example, that a solution remains colorless in the presence of phenolphthalein and is alkaline towards methyl orange, its pH must lie between 8 and 4.5. Should further tests show the unknown to be alkaline also to methyl red, we would know that the pH being measured lies between 6 and 8, and that a suitable indicator could be chosen from the group which includes bromthymol blue, phenol red, neutral red, and cresol red. Universal indicators are especially useful for making such estimates of pH values. 

For introducing the idea of pH values, it is possible at this point, to use the universal indicator to show pH values by different colors. In addition a pH meter may be demonstrated, the pH values interpreted and compared with those of the indicator paper - no hydronium concentrations or logarithms are necessary at this stage. Using these methods, even young students at elementary schools may test several household solutions (see E7.6), and may demonstrate the results on a chart (see Fig. 7.9). 

PH Value. An operational use of the pH term should occure naturally after students have tested various household solutions with universal indicator paper with pH scale - they don t have to deal with any logarithm (see Fig. 7.9). It is more difficult to teach the quantitative meaning of pH value one has to work with concentrations, the logarithm and the mol term. In this case, it is advantageous to relate the meaning of 1 mol to a specific amount of small particles and to decide the type of particles, which are to be counted 18 g water do not contain 1 mol of water , but rather 1 mol of H20 molecules . A liter of 1 M hydrochloric acid contains 1 mol of H30 + (aq) ions and 1 mol of Cl (aq) ions the concentration is equal to 1 mol/1 for both kinds of ions. Dilution in the volume ratio 1 10 results in a solution with the H + (aq) ion concentration of 0.1 mol/1, the dilution 1 100 leads to the 0.01 M or 10 2 M solution. 

Procedure (a) Dilute a little amount of universal indicator solution with tap water, place the green solution in three small beakers (can be projected with an overhead projector). Drop hydrochloric acid into one of the beakers, in the other sodium hydroxide solution, in the third common salt solution. Place several drops of the solutions on strips of universal indicator paper, observe and compare the colors with the color chart, determine the pH values, (b) Fill a large beaker with tap water and add a few ml of phenolphthalein solution while stirring. Prepare a second beaker of the same size with a few drops of sodium hydroxide solution, a third beaker of the same size with a few drops of concentrated sulfuric acid. Pour the contents of the first beaker into the second one, the second one into the third beaker. 

Problem The scale of pH values of adds is unfortunately structured in such a way that along with an increase in concentration of hydronium ions, the pH value decreases that for 1M hydrochloric add or nitric add the pH value 0 results and all diluted solutions show pH values higher than 0. This unusual scale can be studied using universal indicator paper and the pH scale with different colors. This paper can be dipped into solutions from the kitchen, bathroom and laboratory pH values are numerically listed in a tabular form (see Fig. 7.9). 

Material Beakers, pH meter 0.1 M solution of hydrochloric acid, 0.1 M nitric acid and 0.1 M acetic acid, universal indicator paper. 

Material Beakers, two syringes, pH meter hydrogen chloride gas, hydrogen sulfide gas, water, universal indicator paper. 

Universal indicator paper can be used to estimate the pH of a solution. 

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