Universal indicator
From Wikipedia, the free encyclopedia
Universal Indicator is a pH indicator that has different colors to indicate the range of the pH of the solution it is in. This is opposed to indicators like phenolphthalein which have only two different colors and are able to indicate only whether the pH is above or below a certain point by using the various pH values of the indicators. It usually has the following composition:
- Methanol(455)
- Propan-1-ol
- Phenolphthalein, sodium salt
- Methyl red, sodium salt
- Water
- Phenol-4,4'-(3h-2,1-benzoxathiol-3-ylidene)bis-2-bromomethyl-6-(1-methylethyl)-S,S-dioxide, monosodium salt
- Phenol-4,4'-(3h-2,1-benzoxathiol-3-ylidene)bis-5-methyl-2-(1-methylethyl)-S,S-dioxide, monosodium salt
Universal indicator is a flammable liquid. It may cause respiratory tract irritation. Prolonged or repeated contact may cause dry, cracked skin, irritation or kidney damage. It may also form explosive peroxides.
[edit] Colors and meanings
- Very acidic - Red
- Acidic - Orange/Yellow
- Neutral - Green
- Basic/base/alkali - Blue
- Very basic/base/alkali - Purple
The colours follow those of the visible spectrum of light. The pH number is compared with the colour. Anything below 7 is acidic (the lower, the stronger it is acidic), 7 is neutral (neither acidic or alkali) & anything above 7 is alkali (the higher it is, the more alkaline it is). This is easily demonstrated when you put blue litmus paper inside the beaker, it will change its natural alkalinity to a duller/ darker colour if it is of a high pH, or a radiant/ brighter colour if it is of a low pH.
[edit] More details
- Physical state: Liquid
- Appearance: light green in water solvent; dark green alone
- Odour: alcohol-like
- pH value: Approximately 7
- Vapour pressure: 25 mmHg (3.3 kPa)
- Vapour Density: 1.3 kg/m³
- Boiling point: 80 °C
- Solubility: Soluble in water.
- Specific gravity/Density: 0.93 g/cm³
- Molecular formula: Mixture
