Universal indicator
Encyclopedia
A Universal indicator is a pH indicator
composed of a blend of several compounds that exhibits several smooth colour changes over a pH value range from 1-14 to indicate the acidity or basicity of solutions. Although there are a number of commercially available universal pH indicators, most are a variation of a formula patented by Yamada
in 1923. Details of this patent can be found in Chemical Abstracts.
Experiments with Yamada's Universal Indicator are also described in the Journal of Chemical Education.
, phenolphthalein
sodium salt, sodium hydroxide, methyl red
, bromothymol blue
monosodium salt, and thymol blue
monosodium salt.
The colours that indicate the pH of a solution, after adding a universal indicator are:
There are now also available wide range pH test papers with distinct colours for each pH from 1 to 14. Colour matching charts are supplied with the specific test strips purchased.
A universal indicator is a solution which undergoes several colour changes over a wide range of pH's. The colour is used to "indicate" pH directly. Universal indicators are usually mixtures of several indicators.
The easiest universal indicator to prepare is red cabbage juice. Stew red cabbage in water and pour off the water for use as an indicator solution. The pigment in red cabbage juice is anthocyanin, which changes colour from red in acid solution to purplish to green in mildly alkaline solution to yellow in very alkaline solution.
Another universal indicator is used in the classic 'chemical stoplight' demonstration, which changes from green to yellow to red as the pH goes from alkaline to acidic. The indicator is a solution that is 0.05% in each of the following: methyl red, methyl yellow, thymol blue, and bromthymol blue in ethanol.[1]
PH indicator
A pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH of the solution can be determined visually. Hence a pH indicator is a chemical detector for hydronium ions or hydrogen ions in the Arrhenius model. Normally, the indicator causes the...
composed of a blend of several compounds that exhibits several smooth colour changes over a pH value range from 1-14 to indicate the acidity or basicity of solutions. Although there are a number of commercially available universal pH indicators, most are a variation of a formula patented by Yamada
Yamada
Yamada is the 13th most common Japanese surname.-People:*Arinaga Yamada, retainer of Shimazu clan, son of Yamada Arinobu*Arinobu Yamada , retainer of Shimazu clan*Akira Yamada , philosopher...
in 1923. Details of this patent can be found in Chemical Abstracts.
Experiments with Yamada's Universal Indicator are also described in the Journal of Chemical Education.
Details
A universal indicator is typically composed of water, propan-1-olPropan-1-ol
1-Propanol is a primary alcohol with the molecular formula of C3H8O, and a structural formula of CH3CH2CH2OH. It is also known as propan-1-ol, 1-propyl alcohol, n-propyl alcohol, n-propanol, or simply propanol. It is an isomer of isopropanol . It is used as a solvent in the pharmaceutical...
, phenolphthalein
Phenolphthalein
Phenolphthalein is a chemical compound with the formula C20H14O4 and is often written as "HIn" or "phph" in shorthand notation. Often used in titrations, it turns colorless in acidic solutions and pink in basic solutions...
sodium salt, sodium hydroxide, methyl red
Methyl red
Methyl red, also called C.I. Acid Red 2, is an indicator dye that turns red in acidic solutions. It is an azo dye, and is a dark red crystalline powder....
, bromothymol blue
Bromothymol blue
Bromothymol blue is a chemical indicator for weak acids and bases. The chemical is also used for observing photosynthetic activities or respiratory indicators .Bromothymol blue acts as a weak acid in solution...
monosodium salt, and thymol blue
Thymol blue
Thymol blue is a brownish-green or reddish-brown crystalline powder that is used as a pH indicator. It is insoluble in water but soluble in alcohol and dilute alkali solutions. It transitions from red to yellow at pH 1.2–2.8 and from yellow to blue at pH 8.0–9.6.-Bibliography:* Merck. "Thymol...
monosodium salt.
The colours that indicate the pH of a solution, after adding a universal indicator are:
| pH range | Description | Colour |
|---|---|---|
| 0-3 | Strong acid | Red |
| 3-6 | Acid | Orange/Yellow |
| 7 | Neutral | Green |
| 8-11 | Base | Blue |
| 11-14 | Strong Base | Violet/Purple |
There are now also available wide range pH test papers with distinct colours for each pH from 1 to 14. Colour matching charts are supplied with the specific test strips purchased.
A universal indicator is a solution which undergoes several colour changes over a wide range of pH's. The colour is used to "indicate" pH directly. Universal indicators are usually mixtures of several indicators.
The easiest universal indicator to prepare is red cabbage juice. Stew red cabbage in water and pour off the water for use as an indicator solution. The pigment in red cabbage juice is anthocyanin, which changes colour from red in acid solution to purplish to green in mildly alkaline solution to yellow in very alkaline solution.
Another universal indicator is used in the classic 'chemical stoplight' demonstration, which changes from green to yellow to red as the pH goes from alkaline to acidic. The indicator is a solution that is 0.05% in each of the following: methyl red, methyl yellow, thymol blue, and bromthymol blue in ethanol.[1]