Universal indicator paper

Test a small quantity of the aqueous solution or extract of the carboxylic acid with litmus or with Universal indicator paper. 

If an appreciable amount of residue remains, note its colour. Add a few drops of water and test the solution (or suspension) with htmus or with Universal indicator paper. Then add a httle dilute hydrochloric acid and observe whether efiervesceiice occurs and the residue dissolves. Apply a flame test with a platinum wire on the hydrochloric acid solution to determine the metal present. (In rare cases, it may be necessary to subject a solution of the residue to the methods of qualitative inorganic analysis to identify the metal or metals present.) If the flame test indicates sodium, repeat the ignition of the substance on platinum foil. 

Solubility in water. Treat a 0 10 g. portion of the solid with successive 10 ml. portions of water, shaking vigorously after each addition, until 3 0 ml. have been added. If the compound does not dissolve completely in 3 0 ml. of water, it may be regarded as insoluble in water. When dealing with a liquid, add 0 -20 ml. of the compound to 3 0 ml. of water and shake. In either case, test the contents of the small test-tube with htmus (or with Universal indicator paper) it is best to remove a little of the solution or supernatant liquid with a dropper. 

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. 

This solution turns moist universal indicator paper red. It is one of the major pollutant gases and is the gas principally responsible for acid rain. However, it does have some uses as a bleaching agent for paper manufacture, in fumigants and in the preservation of food by killing bacteria. 

In a 100-ml conical flask place 5.5 g (0.015 mol) of methyl 2,3,4,6-tetra-O-acetyl-/ -D-glucopyranoside (Expt 5.111), 50 ml of dry methanol and 10ml of a solution of sodium methoxide in methanol previously prepared by the cautious addition of 0.1 g of sodium to 20 ml of methanol. Stopper the flask and allow the solution to stand for 1 hour, then add sufficient ion exchange resin [Zeolite 225 (H )] to render the solution neutral to moist universal indicator paper. Remove the resin by filtration, wash with methanol and evaporate the combined filtrate and washings under reduced pressure (rotary evaporator). Triturate the colourless syrup with absolute ethanol to cause it to solidify and recrystallise from absolute ethanol. The pure methyl / -d-glucopyranoside has m.p. 108-109 °C, [oc]d° —30.2° (c2.8 in H20) the yield is 2.4 g (83%). 

Universal indicator paper moistened with distilled water gives a satisfactory indication of neutralisation. 

Phloroisobutyrophenone is unstable when heated in the presence of acid the addition of Rochelle salt prevents the precipitation of aluminium hydroxide when the free acid is neutralised with sodium hydroxide. If any precipitate does appear more Rochelle salt should be added the exact amount of aqueous sodium hydroxide will vary with each experimental sequence the point of neutrality is ascertained with universal indicator paper. 

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. 

---