VOLUME 33, NO. 10, OCTOBER, 1956
UNIVERSAL INDICATOR FOR pH 1-13 P. R. RICHARDSON Royal Military College of Canada, Kingston, Ontario
.~
IT IS convenient to use colorimetric n H- rnearnlrement,s .--.....- 0.255 x. bromothvmol blue in 4 ml. 0.1 N NaOH + minimum vOIUmemethaGol for experiments in the f i s t year general chemistry 0.250 g. thymol blue in 4 ml. 0.1 N NaOH minimum volume laboratory to demonstrate buffer action, common ion ",eli"il""l effect, and relative strengths of acids a i d bases. We have found that available universal indicators are not These solutions were mixed and diluted to one liter n H range. with methanol and filtered. The mixed indicator entirelv satisfactorv a t the extremes of- t,hn -r-~artictharlva t the ilkaline end. The followine mixture gave the following - color changes: bf indicators is quite satisfactory to differentiate inteaH Color aH Color 1 red pink gral pH units over the range p ~ i - 1 3 : 7 green yellow ~
+
-..LL.-.,
-
-----0-7
1.250 g. syn-trinitrobenzene in 25 ml: dioxane 0.040 g. phenolphthalein in 20 ml. methanol 0.300 g. o-cresol phthalein in 30 ml. methanol 0.125 g. meta methyl red in 50 ml. methanol 0.125 g. metanil yellow in 30 ml. methanol 0.010 g. methyl orangein20 ml. methanol 1,000 g, albarin yellow GG in ml, methanol + 20 ml dioxane 0.025 g. methyl red in 100 ml. methanol 20 ml. dioxane
+
2 pale orange pink 3 oranee 5 orange yellow
6 pale yellow
13 brawn orange (fades
8 green 9 blue ereen
11 iedpurple
iiwgple Orange
The above description in words does not adequately describe the marked differences in color observed. In practice the pH can be readily estimated to within 0.5 pH units from a series of standards.
